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Shinjiro Suzuki, Hayato Sakai, [Mitsuaki Yamauchi](https://orcid.org/0000-0003-0005-5960), [Hironobu Hayashi](https://orcid.org/0000-0002-7872-3052), [Yoshiyuki Mizuhata](https://orcid.org/0000-0001-5301-0024), Tatsuhisa Kato, [Takashi Hirose](https://orcid.org/0000-0002-5351-2101), [Taku Hasobe](https://orcid.org/0000-0002-4728-9767), [Hiroko Yamada](https://orcid.org/0000-0002-2138-5902)

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[Observation of Photophysical Processes of a Heptacene Derivative: Monomeric Behavior in Homogeneous Solution and Singlet Fission in Thin Film](https://mdr.nims.go.jp/datasets/e30db8c9-c095-4160-ad5e-8ecec0eb9d26)

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Observation of Photophysical Processes of a Heptacene Derivative: Monomeric Behavior in Homogeneous Solution and Singlet Fission in Thin FilmObservation of Photophysical Processes of a Heptacene Derivative:Monomeric Behavior in Homogeneous Solution and Singlet Fissionin Thin FilmShinjiro Suzuki, Hayato Sakai, Mitsuaki Yamauchi, Hironobu Hayashi, Yoshiyuki Mizuhata,Tatsuhisa Kato, Takashi Hirose,* Taku Hasobe,* and Hiroko Yamada*Cite This: J. Am. Chem. Soc. 2026, 148, 6000−6011 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: A soluble heptacene derivat ive , 5 ,9 ,14,18-tetrakis-(triisopropylsilylethynyl)-heptacene (TIPS-Hep), was synthesized in situ froman α-diketone precursor via the Strating−Zwanenburg reaction, and itsphotophysical properties were comprehensively characterized in both solutionand thin-film states. In deoxygenated dilute tetrahydrofuran (THF) solution,TIPS-Hep exhibited monomeric behavior. Absorption peaks were observed at 671,737, 820, and 970 nm, accompanied by a shoulder at 870 nm, while fluorescencepeaks were observed at 894 and 961 nm with a fluorescence lifetime (τS) of <100ps. Nanosecond transient absorption spectroscopy revealed a triplet lifetime (τT)of 19 μs and a triplet quantum yield (ΦISC) of ∼2%. The short excited-statelifetime in dilute solution was estimated to be 87 ps by femtosecond transientabsorption spectroscopy and precludes efficient molecular encounters, indicatingthat singlet fission is unlikely and that intersystem crossing serves as the dominantpathway for triplet formation. This interpretation is supported by transient decay analysis, which revealed no kinetic signaturesassociated with SF. In contrast, solution-processed thin films of TIPS-Hep, generated in situ by photoirradiation of a spin-coated α-diketone precursor, exhibited faster and enhanced formation of the triplet excited states. Since multiple excited species are involved,several kinetic models were examined, and a sequential model based on a SF pathway (S1 + S0 → TT → 2T1) was identified as themost consistent with the experimental results. Global analysis of femtosecond transient absorption data with the sequential SF modelassuming three species revealed high yields of correlated triplet pairs (TT, 75% at the maximum value of 100%) and independenttriplets (T1, 20% at the maximum value of 200%). These results provide valuable mechanistic insights into the excited-state dynamicsof higher acenes.■ INTRODUCTIONLinearly fused higher acenes, especially those containing morethan five benzene rings, have garnered significant interest dueto their potential in near-infrared (NIR) optoelectronics andorganic semiconductors.1−6 Their distinct optical and elec-tronic properties arise from extended π-conjugation and zigzag-edged structures, making them ideal model systems forexploring magnetism in carbon-based nanostructures. How-ever, this same structural motif results in an exceptionallynarrow highest occupied molecular orbital (HOMO)−lowestunoccupied molecular orbital (LUMO) gap with increasingacene length, compromising intrinsic stability. Moreover, theplanar architecture and lack of solubilizing functional groupshinder their solubility, constraining their processability anddevice integration.Among the synthetic strategies for higher acenes, theStrating−Zwanenburg reaction has proven to be particularlyeffective (Figure 1).7 This visible-light-induced photodecarbo-nylation of α-diketones proceeds cleanly with gaseousbyproducts, enabling the efficient formation of targetacenes.8−12 Using this approach, higher acenes have beenaccessed and characterized in matrices at cryogenic temper-atures,13,14 single crystals,15 metal−organic frameworks,16,17and via on-surface synthesis under ultrahigh vacuum.18−23These advances have facilitated detailed investigations of theirelectronic structures. Thermal strategies have also beenemployed, including the cycloreversion of diheptacenes24 andthermal decarbonylation of monoketone heptacene precur-sors,25−28 though these typically require oxygen-free con-ditions.Despite significant advances in understanding the photo-physics of acenes less than pentacene,1,29 the excited-stateReceived: August 23, 2025Revised: December 26, 2025Accepted: January 21, 2026Published: February 5, 2026Articlepubs.acs.org/JACS© 2026 The Authors. Published byAmerican Chemical Society6000https://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−6011This article is licensed under CC-BY-NC-ND 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on April 10, 2026 at 08:37:48 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shinjiro+Suzuki"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hayato+Sakai"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Mitsuaki+Yamauchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hironobu+Hayashi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yoshiyuki+Mizuhata"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tatsuhisa+Kato"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tatsuhisa+Kato"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Hirose"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Taku+Hasobe"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hiroko+Yamada"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/jacs.5c14689&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=tgr1&ref=pdfhttps://pubs.acs.org/toc/jacsat/148/6?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/6?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/6?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/6?ref=pdfpubs.acs.org/JACS?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://pubs.acs.org/JACS?ref=pdfhttps://pubs.acs.org/JACS?ref=pdfhttps://creativecommons.org/licenses/by-nc-nd/4.0/behavior of pristine heptacene in solution at room temperatureremains largely unexplored, primarily due to its extremely lowsolubility.17,24,30−32 Its fluorescence spectrum in solution has,to date, eluded experimental observation, most likely due to itsexceptionally low fluorescence quantum yield. This isconsistent with spectroscopic and theoretical studies of up tohexacene, which reveal an acceleration of internal conversionwith increasing acene length.24,33 Recently, fluorescence fromheptacene was detected at 77 K within a metal−organicframework (MOF) host using the photoprecursor, 7DK1.17Neckers et al. successfully observed transient heptacenegenerated by nanosecond laser flash photolysis of 7DK1 intoluene, reporting the intersystem crossing (ISC) from the S1to T1 state of heptacene with a lifetime of ∼7 ns, along with atriplet−triplet absorption at 580 nm decaying in 10.6 ± 0.1μs.13 The extremely low triplet energies of heptacenederivatives hinder the accurate determination of ISC quantumyields, and no Jablonski diagram with quantitativelydetermined quantum yields and rate constants for each processhas yet been reported so far. While substituted heptaceneshave been synthesized to improve solubility and stability,30,32,34comprehensive analyses of their excited-state dynamics remainabsent.Acenes are known to be excellent candidates for singletfission (SF), where an excited singlet state (S1) transfersenergy to a neighboring ground-state molecule to form acorrelated triplet pair (TT). SF has emerged as a promisingroute to boost photovoltaic efficiencies beyond the Shockley−Queisser limit (eq 1)35−38S S TT 2T0 1 1+ (1)Extensive studies on tetracene and pentacene haveelucidated the SF mechanism, particularly when E(S1) ≥2E(T1).39−58 Although SF was reported in hexacenederivatives (E(S1) = 1.8 eV, E(T1) = 0.4 eV),59 experimentalevidence for SF in heptacene remains absent. Theoreticalpredictions place E(T1) of heptacene between 0.24 and 0.69eV,60−62 with E(S1) around 1.54 eV.59 The sufficient energydifference between E(S1) and 2 × E(T1) suggests that SF inheptacene is thermodynamically feasible. While the low E(T1)renders heptacene inefficient for photovoltaic applications,investigations of SF in heptacene and its derivatives offervaluable mechanistic insights into the excited-state dynamics ofhigher acenes.Herein, we report the design, synthesis, and photophysicalcharacterization of 5,9,14,18-tetrakis(triisopropylsilylethynyl)-heptacene (TIPS-Hep), achieving a long-sought advance inthe photophysics of higher acenes through the stableobservation of heptacene fluorescence in solution at roomtemperature. The strategic placement of four TIPS-ethynylgroups at previously unreported substitution sites not onlyensures high solubility in solution but also affords a materialthat can be handled under deaerated conditions for detailedtime-resolved studies in both solution and thin-film states. Thesynthetic accessibility of TIPS-Hep via the in situ Strating−Zwanenburg reaction (Scheme 1), its sufficient stability for thespectroscopic measurements, and its distinctive excited-statedynamics collectively position it as a valuable platform forunraveling the fundamental photophysics of higher acenes andadvancing their application in optoelectronic devices.■ RESULTS AND DISCUSSIONThe α-diketone precursor, TIPS-7DK, was synthesized asoutlined in Scheme 2, beginning with the preparation of1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene (1) as a mixtureof stereoisomers following the reported procedure.63 Itsreaction with 1,4-naphthoquinone in the presence of 3,6-di-2-pyridyl-1,2,4,5-tetrazine yielded a tetraone-diepoxy hepta-cene framework 2. Insoluble stereoisomers were removed byfiltration, and the filtrate was further converted to heptacene-5,9,14,18-tetraone (3). Subsequent ethynylation with lithiumtriisopropylsilylethyn-1-ide and methylation furnished com-pound 4, which was transformed through a Diels−Alderreaction with vinylene carbonate, deoxygenative aromatizationFigure 1. Synthesis of heptacene from photo- and thermal precursors.Scheme 1. Photoconversion from TIPS-7DK to TIPS-HepJournal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116001https://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=sch1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=sch1&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-aswith SnCl2, base-promoted hydrolysis, and Swern oxidation tothe target α-diketone precursor, TIPS-7DK. Structures ofintermediates were confirmed by 1H and 13C NMR spectros-copy and high-resolution mass spectrometry.To generate TIPS-Hep for spectroscopic studies, TIPS-7DK was dissolved in a deoxygenated solvent inside aglovebox, using either an NMR sample tube or an opticalcell equipped with a J. Young valve. The solution was thenirradiated with a 470 nm LED light (400 mW cm−2) for 20min (Scheme 1). Complete conversion from TIPS-7DK toTIPS-Hep was confirmed by NMR spectroscopy (FigureS1a,b), with no detectable byproducts such as heptacenedimers. To measure the absorption spectrum of pure TIPS-Hep in CDCl3, the solution was transferred to an optical cell,and the spectrum was recorded immediately following theNMR measurement (Figure S1c).The evolution of the absorption spectrum during thephotoconversion from TIPS-7DK to TIPS-Hep in THF isshown in Figure 2a−d. Upon photoirradiation, broadabsorption band of α-diketone TIPS-7DK around 453 nmgradually diminished, while new peaks emerged at 671, 737,820, and 970 nm, accompanied by a shoulder at 870 nm,indicating the formation of TIPS-Hep. It is noteworthy thatthe appearance of the weak absorption band at 970 nm isconsistent with the feature previously reported for 6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene�an isomer ofTIPS-Hep (6,8,15,17-TIPS-Hep) reported by Bunz et al.31,32Although the assignment of the weak band at 970 nm remainsunder discussion, it is most plausibly attributed to thesymmetry-forbidden S1 (1Ag) ← S0 transition.24 The molarabsorption coefficients of both TIPS-7DK and TIPS-Hepwere determined in THF (Figure 2e,f). For reference, pristineheptacene�previously reported in 1-methylnaphthalene at230 °C�exhibits absorption maxima at 623, 682, and 753 nmwith a shoulder at 792 nm.24 Compared to pristine heptacene,TIPS-Hep shows red-shifted absorption maxima by 50−70nm, attributable to π-expansion through incorporation of theTIPS-ethynyl groups. Notably, the absorption spectrum of6,8,15,17-TIPS-Hep in CH2Cl2 (10 μM) displays its mostintense absorption at 865 nm, with a shoulder at 900 nm and asmall peak at 1040 nm. The main peak is further red-shifted by45 nm relative to TIPS-Hep.31,32 These observations suggestthat the electronic structure of TIPS-Hep more closelyresembles that of pristine heptacene than that of the6,8,15,17-TIPS-substituted isomer.Heptacene has been reported to possess a biradical characterin the ground state and readily undergoes dimerization insolution, particularly in the unsubstituted form.24,64 To addressthe possibility of dimerization during the measurement, theabsorbance at 820 nm was monitored at various concen-trations. No significant spectral changes were observed up to60 μM (Figure S2), and no evidence of dimer formation wasdetected within 300 s at 50 μM at ambient temperature(Figure S3a). When the solution was stored under an Aratmosphere in the dark at ambient temperature for 24 h, thepeaks at 671, 737, and 820 nm diminished by half, suggestingthat slow dimerization occurs in the dark (Figure S3b,c). Bynormalization at 671 nm, the relative intensities at 671, 737,820, 870, and 970 nm of the absorption spectra before andafter 24 h remained unchanged, confirming that all these peaksoriginate from a single species, TIPS-Hep (Figure S3a). Thechange in the absorption spectrum of a TIPS-Hep solution at ahigher concentration (200 μM) was monitored in the dark for72 h (Figure S4). The absorption peaks of TIPS-Hepdiminished and new peaks characteristic for shorter acenesincreased. There are isosbestic points at 321, 420, 455, 486,510, 525, and 553 nm. The change of 1H NMR spectra ofTIPS-Hep was also monitored at the same concentration(Figure S5). After 48 h, the formation of several byproductswas evident, characterized as several dimeric species by typicalbridgehead proton signals at 6.13, 5.32, and 5.26 ppm.The fluorescence spectra of TIPS-Hep in THF at roomtemperature exhibited emission peaks at 894 and 961 nm uponexcitation at 820 nm (Figure 3a). By excitation at 350 nm, thefluorescence peaks were observed at the same wavelengths, andno emission was observed over 1000 nm (Figure S6). Therelative fluorescence quantum yield (ΦFL′) was estimated as0.020% using indocyanine green as a standard (ΦFL = 5.1%)Scheme 2. Synthetic Scheme of TIPS-7DKJournal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116002https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=sch2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=sch2&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as(Figure S7 and Table S1).17 The fluorescence lifetime (τFL′)was measured to be less than 0.1 ns (20 μM, λex = 820 nm, λem= 910 nm), limited by the instrument response function,suggesting a remarkably fast nonradiative decay rate (knr′ > 1.1Figure 2. (a)Absorption spectral changes of TIPS-7DK in THF (50 μM) upon photoirradiation. (b) Magnified spectra in the 600−1100 nmregion. Optical path length: 1 mm. (c) Time-dependent absorbance changes at 453 and 820 nm and (d) normalized time-dependent absorbancechange at 453, 820, 870, and 970 nm during the photoconversion from TIPS-7DK to TIPS-Hep. (e) Molar absorption coefficients of TIPS-7DKand TIPS-Hep in THF. (f) Magnification (15 times) at 600−1100 nm.Figure 3. (a) Absorption (red) and fluorescence (blue, λex = 820 nm) spectra of TIPS-Hep in THF (20 μM). Optical path length: 10 mm. (b,c)Normalized absorption and fluorescence excitation spectra (λem = 900 and 950 nm) of TIPS-Hep in THF. (b) 300−1100 nm region (0.4 μM). (c)500−1100 nm region (0.4 and 10 μM).Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116003https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig3&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as× 1010 s−1) (Figure S8). The vibrational progression (ΔΕ) ofthe absorption and emission spectra were 1373 cm−1 (737−820 nm for absorption) and 780 cm−1 (894−961 nm foremission), respectively (Figure S9). The ΔΕ of the absorptionbands were well reproduced by theoretical calculations at theRTD-CAM-B3LYP/6-31G(d) level using an adiabatic Hessianpotential model (Figures S11−S13), whereas ΔΕ of theemission progression could not be reproduced by the samemodel.Fluorescence excitation spectra were measured in THF bymonitoring at 900 and 950 nm at the concentrations of 0.4 and10 μM (Figure 3b,c). The peaks of the excitation spectra wereobserved around 800 and 860 nm, which are inconsistent withthe main absorption bands at 737 and 820 nm. Due to the lowsensitivity of the fluorescence excitation spectrum in the near-infrared region, the peak maxima cannot be determinedprecisely. Nevertheless, the ΔΕ between the bands at 860 and800 nm is estimated to be ∼870 cm−1, which is close to the ΔΕof the emission peaks at 894 and 961 nm (∼780 cm−1). Thesefindings indicate that the fluorescence likely originates fromthe 870 nm shoulder, which is characteristic of heptacenederivatives.31,32 The 870 nm absorption and corresponding894/961 nm emission are therefore attributed to an electronicstate in equilibrium with the ground state of TIPS-Hep. Whilethe precise nature of this emissive species is not yet fullyunderstood, similar shoulder absorption bands in extendedacenes have often been discussed in the context of a singletbiradical form.65,66 Consequently, the weak peak at 970 nm isattributed to the dipole-forbidden S1 (21Ag) ← S0 (11Ag)transition,24,67 while the main absorption bands at 671, 737,and 820 nm correspond to the dipole-allowed S2 (11B2u) ← S0(11Ag) transition. Meanwhile, the weak shoulder around 870nm is assigned to a transition associated with an alternativeemissive state that exists in thermal equilibrium with theground state. This interpretation rationalizes both the distinctvibronic spacings between absorption (∼1370 cm−1) andemission (∼780 cm−1) and the observation of emission from ahigher-energy state (λem = 894 nm) relative to the lowest-energy absorption band (∼970 nm). While definitiveexperimental or computational evidence for the emissivespecies is not yet available, the consistency between thevibronic progressions of the excitation and emission spectra(∼780 cm−1), strongly suggests that emissive state is inequilibrium with the ground state of TIPS-Hep.To gain theoretical insights into the absorption and emissionproperties of TIPS-Hep, its optimized ground (S0)-stategeometry and excited states were calculated using time-dependent density functional theory (TD-DFT) and completeactive space self-consistent field (CASSCF) methods. Theexcited-state calculations, based on the optimized S0 geometry,employed the multireference CASSCF method, which isessential for describing dipole-forbidden excited states (1Ag)that involve significant double excitation character.17 Asreference systems, calculations for pristine pentacene andheptacene at the CASSCF(6,6)/def2-SVP//RCAM-B3LYP-GD3BJ/6-31G(d) level reproduced the established inversionin the symmetry of their S1 states: the S1 state of pentacene isdipole-allowed (1B2u), whereas that of heptacene is dipole-forbidden (1Ag), in agreement with previous theoretical studies(Table S2).24,67 Building on this finding, we performedcalculations at the same theoretical level for the TIPS-substituted analogues, 6,13-bis(triisopropylsilylethynyl)-Figure 4. (a) Nanosecond transient absorption spectra (ns-TAS) of Ant (300 μM) in the presence of TIPS-Hep (5.0 μM) in THF. λex: 355 nm.(b) The time profiles of TIPS-Hep (5.0 μM) in Ant solution (300 μM in THF) at 425 nm (black) and 675 nm (red). (c) The corresponding time-profiles of Ant (300 μM) at 425 nm in the presence of different concentrations of TIPS-Hep (0−14 μM). Absorbance at 425 nm was normalized atthe initial absorbance. Inset: pseudo-first order plot of τ0/τ monitored at 425 nm versus concentrations of TIPS-Hep. (d) The estimated εT valuesof TIPS-Hep in THF.Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116004https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig4&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-aspentacene (TIPS-Pen) and TIPS-Hep. The results revealedthat the bulky TIPS-ethynyl groups do not alter the S1-stateordering; notably, TIPS-Hep retains a dipole-forbidden S1state (1Ag), indicating that its excited-state dynamics primarydepend on the electronic structure of the heptacene backbonerather than by substituents. The diradical character (y0) ofpentacene, TIPS-Pen, heptacene, and TIPS-Hep wereestimated as 0.378, 0.367, 0.629, and 0.810, respectively,suggesting significantly large diradical character (∼81%) ofTIPS-Hep.Experimentally, the electron spin resonance (ESR) spectrumof TIPS-Hep at room temperature showed no detectable signal(Figure S10), in contrast to a previous report.31 Consistentwith this EPR-silent nature, the 1H NMR spectrum of TIPS-Hep exhibited sharp resonances, indicating a lack of significantparamagnetic broadening. To gain deeper insight into theelectronic structure, we performed theoretical calculations ofTIPS-Hep at the UCAM-B3LYP/6-31G(d) level (Figures S14and S15). Broken-symmetry (BS) DFT calculations revealedthat the BS singlet state is more stable than the closed-shellsinglet state by 30.1 kJ mol−1. The resulting spin density isprimarily localized along the zigzag edges of the heptacenecore, that is typical for the higher acenes.Furthermore, the optimized geometry of the BS stateexhibits significantly reduced bond length alternation (BLA)compared to the closed-shell state, which is consistent with itshigh diradical character (Figure S15). These results, combinedwith the lack of an EPR signal, confirm that the ground state isa singlet (S = 0). This state is best described as a singletdiradicaloid rather than a traditional closed-shell molecule; theα and β spins are antiferromagnetically coupled, maintainingan EPR-silent singlet state while possessing significant diradicalcharacter.To elucidate the triplet-state properties, measurements ofnanosecond transient absorption spectra (ns-TAS) wereperformed on a 5.0 μM solution of TIPS-Hep in THF inthe presence of 300 μM anthracene (Ant; a triplet sensitizer),upon excitation of Ant at 355 nm (Figure 4a). At 1 μs afterexcitation, a transient absorption (TA) peak at 425 nm,corresponding to the triplet state (T1) of Ant (3Ant*), wasobserved. This signal decreased over time, while a newabsorption band of TIPS-Hep at 675 nm, assignable to the T1state of TIPS-Hep sensitized via triplet−triplet energy transfer(TTET) from 3Ant*, gradually appeared. Kinetic analysis at675 nm yielded a triplet lifetime (τT) of 19 μs (Figure 4b).Consistently, the decay profile at 425 nm indicated efficientquenching of 3Ant*, with a second-order rate constant forTTET from 3Ant* to TIPS-Hep estimated as 4.8 × 109 M−1s−1 (Figure 4c). This rate constant approaches the diffusion-controlled limit in THF (1.4 × 1010 M−1 s−1 at 298 K).68 Thetriplet molar absorption coefficient (εT) of TIPS-Hep wasestimated as 98,000 M−1 cm−1 at 675 nm (Figure 4d and TableS3), which was subsequently employed in the analysis offemtosecond transient absorption spectra (fs-TAS). Notably,the triplet signals from TIPS-Hep were not observed in theNIR region (ca. 1000−1500 nm) as described later in the fs-TAS measurements (Figure 5 and also see Figure S16).The fs-TAS of a 600 μM THF solution of TIPS-Hep excitedat 740 nm are shown in Figure 5a. Within 8.0 ps afterphotoexcitation, the TA bands attributed to the S1 state ofTIPS-Hep appeared in the 450−550 nm region with a vibronicstructure, along with a sharp peak at 670 nm and 1100−1500nm which decayed within 100 ps (Figure 5b). At 2000 ps, onlya weak residual peak remained at 670 nm, which is assigned tothe T1 state of TIPS-Hep (Figure 5a). This result indicatesthat the peak at 670 nm includes contribution from both S1→Sn and T1→Tn transitions. Global analysis with a sequentialmodel identified two species: the relaxed S1 state and the T1state (Figure 5d,e). The lifetime of S1 state (τS) was estimatedto be 87 ps. As TIPS-Hep exists as monomers under theseconditions, the T1 state observed at 2000 ps is thought tooriginate from ISC from the S1 state. We also evaluated theFigure 5. (a) Femtosecond transient absorption spectra (fs-TAS) of TIPS-Hep in THF (600 μM) irradiated at 740 nm, 0.64 μJ. Inset: anexpansion of the spectrum at 2000 ps. (b) Time-profile at 666 (red) and 1400 (black) nm peaks and (c) magnification (10 times). (d) Species-associated spectra and (e) time-dependent population dynamics of S1 and T1 states.Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116005https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig5&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asmolar absorption coefficients of the S1 state (εS) from the fs-TAS of TIPS-Hep (in THF) as described in Figures 5d andS16. The εS at 670 nm (1,400,000 M−1 cm−1) is approximately15 times larger than that of the corresponding εT (98,000 M−1cm−1 at 675 nm). In THF, TIPS-Hep exhibits similar spectralshapes in both the S1 and T1 states across the visible range(500−700 nm), but the maximum εT value is at least 1 order ofmagnitude smaller than the εS value. In contrast, in the NIRregion (ca. 1000−1500 nm), the TA of the S1 state exhibitsbroad absorption bands, whereas that of the T1 state fallsbelow the detection limit due to the signal-to-noise ratio. Thedecay traces at 666 and 1400 nm (Figure 5b) exhibit highlyconsistent behavior up to approximately 300 ps. However, at1000 ps, while the ΔAbs remains positive at 666 nm, itapproaches zero at 1400 nm (Figures 5c). These observationssuggest that the singlet-to-triplet conversion processes�suchas ISC and SF, discussed later�should be carefully consideredin terms of (i) the similarity of the TA spectral featuresbetween the S1 and T1 states and (ii) the remarkably intense S1signal. Additionally, excitation at 870 and 970 nm yielded thesame results (Figures S17 and S18), indicating that theobserved dynamics are independent of the excitation wave-length. As discussed earlier, the main singlet biradical groundstate (S0) and the emissive ground state (S0′) of TIPS-Hepexist in thermal equilibrium. The lack of excitation-wavelengthdependence in the transient absorption spectra thereforesuggests that the dynamics primarily originate from the singletbiradical species, which is more populated at equilibrium andintrinsically exhibits a stronger TA signal.Separately, measurement of picosecond transient absorptionspectra (ps-TAS) upon direct excitation of TIPS-Hep in THF(Figure S19) also revealed the triplet−triplet absorptionthrough ISC process. Using the εT value estimated from ns-TAS (Figure 4d), the ISC quantum yield (ΦISC) wasdetermined to be 2.4 ± 0.7% along with τT = ∼ 10 μs.Based on the undetectable fluorescence from the S1 state andΦISC (∼2%), the nonradiative quantum yield (ΦNR) wasapproximately estimated to be ∼98%. Consequently, the rateconstants of ISC (kISC) and nonradiative decay (kNR) wereestimated to be 2.8 × 108 and 1.1 × 1010 s−1, respectively(Figure 6a and Table 1).The kinetic models and rate constants of TIPS-Hep aresummarized in Figure 6a and Table 1, in comparison withTIPS-Pen (Figure S20), a benchmark acene derivative.According to previous reports, the values of kFL, kNR, andkISC of TIPS-Pen are 5.8 × 107, 6.9 × 106, and 1.2 × 107 s−1,respectively (Table 1). In contrast, the values of kNR and kISCfor TIPS-Hep are 1.1 × 1010 and 2.8 × 108 s−1, respectively,with a remarkably high ΦNR of 98% (vide supra). Themarkedly different deactivation dynamics between TIPS-Hepand TIPS-Pen�namely, the absence of detectable emissionfrom the S1 state and the significantly enhanced nonradiativedecay rates (kNR and kISC) in TIPS-Hep�are indicative of thefundamentally distinct electronic nature of their S1 states.TIPS-Pen exhibits prominent emission via the dipole-allowedS1 (11B2u) → S0 (11Ag) transition (kFL = 5.8 × 107 s−1, ΦNR =75%), whereas TIPS-Hep shows no detectable emission fromthe S1 state. The markedly enhanced nonradiative decay inTIPS-Hep is likely associated with a symmetry-allowedinternal conversion from the dark S1 (21Ag) state to the S0state (11Ag) of the same symmetry. Enhanced nonradiativedecay with increasing numbers of annulated rings has also beenobserved for pristine acenes: the singlet lifetime (τS) ofpentacene is 83 ns,33 while that of heptacene is less than 7 ns.13Figure 6. Kinetic models and corresponding photophysical parameters of TIPS-Hep (a) in THF and (b) in film. The parameters in (a) aresummarized in Table 1. 1FL*: the excited state of the emissive state. The kNR′ is derived from results obtained in THF solution and should be notedas an apparent value. In film, kNR″ denotes the effective nonradiative decay constant, which includes both S1 → S0 internal conversion and S1 → T1intersystem crossing. Since kISC is much smaller than kNR, it can be considered negligible.Table 1. Summarized Photophysical Properties of TIPS-Pen and TIPS-Hep.acompd solventkFL′b/107 s−1(ΦFL′/%)kNR′b/1010 s−1(ΦNR′/%)kFLd/107 s−1(ΦFL/%)kNRd/1010 s−1(ΦNR/%)kISCd/107 s−1(ΦISC/%) τSe/ns τTe/μsTIPS-Penf Me-THF − − 5.8h (75)g 0.00069h (9)h 1.2h (16)f 13g 24fTIPS-Hepi THF >0.2 (>0.02)c ∼1 (<99.98) − 1.1j (97.6)k 28j (2.4)k 0.087j 10jaKinetic model of TIPS-Hep and TIPS-Pen in solution are shown in Figures 6a and S18, respectively. bRate constants and quantum yields of theemissive state (S0′), estimated assuming a thermal equilibrium between two ground-state species (S0 and S0′). The relative magnitudes of the rateconstants are governed by this equilibrium. kFL′: fluorescence rate constant, defined as kFL′ = ΦFL′/τFL′, where ΦFL′ is the fluorescence quantumyield and τFL′ is the fluorescence lifetime. kNR′: nonradiative rate constant, defined as kNR′ = (1−ΦFL′)/τFL′. ΦNR′: quantum yield of internalconversion, defined as ΦNR′ = 1−ΦFL′. cBecause the absorptions of S0 and S0′ overlap at the excitation wavelength (λex = 740 nm), ΦFL′ representsa lower limit. dRate constants and quantum yields of the ground state (S0). kFL: fluorescence rate constant, defined as kFL = ΦFL/τFL, where ΦFL isthe fluorescence quantum yield and τFL is the fluorescence lifetime. kNR: nonradiative rate constant, defined as kNR = ΦNR/τS, where ΦNR is thequantum yield of internal conversion, given by ΦNR = 1−ΦFL−ΦISC. ΦISC: quantum yield of intersystem crossing, determined from ps-TASmeasurements. eτS: lifetime of the singlet-excited state, defined as τS = 1/(kFL + kNR + kISC). τT: lifetime of the triplet-excited state, defined as τT =1/kT, where kT is the decay constant of the triplet-excited state.fReported value in Me-THF.69 gReported value in CHCl3.43 hValues estimatedusing the reported kFL, ΦFL, ΦISC, and τS1 listed in this table. iThis work. jAccording to target analysis, the uncertainty in the rate constants andlifetimes is approximately ±3%. kThe standard deviations for ISC and NR are ±0.7%. See the SI for details of the calculations.Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116006https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asIn contrast to diluted solutions, where molecules aredispersed in isolation, bulk solids are expected to exhibitmore complex excited-state dynamics involving multiplemolecules as a result of intermolecular interactions. Toinvestigate the excited-state dynamics of TIPS-Hep in thesolid state, spin-coated films of TIPS-Hep were prepared fromTIPS-7DK on quartz substrates and subsequently photo-irradiated with a 470 nm LED lamp for 1 h at 50 °C in aglovebox. The absorption spectra recorded before and afterphotoirradiation are shown in Figure S21. The absorptionpeaks are similar in shape to those observed in THF, with onlyslight wavelength shifts, indicating that TIPS-Hep does notundergo significant aggregation in the film state. This behaviorcontrasts with pristine heptacene, which has been reported toform aggregates in films and in single crystals, exhibiting broadabsorption bands around 900 nm.15,24 XRD measurements ofthe TIPS-Hep films on silicon (Si) substrates exhibited nodiffraction peaks (Figure S22), consistent with an amorphouscharacter. Although these substrates differ from quartzsubstrates used for the film fs-TAS measurements, both filmsexhibited similar appearance, suggesting that the quartz-basedfilms are also amorphous character. Furthermore, AFM imageson the Si-supported films revealed smooth film surfaceswithout notable grain boundaries or roughness (Figure S23),corroborating the absence of significant aggregation orcrystallization upon spin-coating of TIPS-7DK and subsequentphotoirradiation. Thus, the introduction of bulky TIPS-ethynylsubstituents at the 5,9,14,18-positions of the heptacenebackbone effectively suppresses strong intermolecular inter-actions which induce crystallization, dimerization or excimerformation in the film.The fs-TAS measurements of the TIPS-Hep film under air(λex = 740 nm) revealed an initial broad absorption spanning450−550 and 1000−1500 nm, along with a sharp band at 690nm, characteristic of the S1 state absorption (Figure 7a andS24a). Over time, the broad features decayed while the 690 nmband persisted, which can be attributed to overlapping S1→Snand T1→Tn transitions. The decay in Figure 7b and S24b showpositive TA contributions mainly from the S1 state at 514 nm,and from both S1 and T1 states at 620 nm, while a negative TAsignal corresponding to ground-state bleaching (GSB) wasobserved at 815 nm. The sharp S1 band exhibited a slightredshift from 670 nm in THF to 690 nm in the film, whereasthe GSB shifted only marginally from 820 in THF to 815 nmin the film. The notable redshift in the solid state indicatesintermolecular interactions among the TIPS-Hep molecules,despite the steric hindrance imposed by the bulky TIPS-ethynyl groups. The more pronounced redshift of the S1 signalrelative to the GSB suggests that these interactions are strongerin the S1 state than in the ground state.As demonstrated by the fs-TAS results in THF solution, theS1 and T1 spectra of TIPS-Hep are clearly distinguishable inthe NIR region. In the thin-film fs-TAS measurements,transient absorption signals attributable to the S1 stateappeared immediately after photoexcitation at 740 nm,spanning 1000−1500 nm, and decayed with time. The timeprofiles at 514 and 620 nm exhibited two decay components,whereas that at 815 nm showed both a decay and a rise. Thetransient trace at 815 nm, corresponding to the GSB, isconsistent with the global analysis model, although therelatively low signal-to-noise ratio in this NIR region precludesa definitive assignment of the subtle deepening observed in thefirst 10 ps. Although no further spectral evolution was observedafter 300 ps, the ΔAbs values did not return to zero, suggestingthat at least three excited species participate in the relaxationdynamics. Comparison of Figures 5 and 7 indicates that thedecay of the S1 state and the concomitant rise of the T1 stateare significantly accelerated in the solid state relative to thesolution. This enhancement in triplet formation could arisefrom several possible pathways, including (i) acceleratedintersystem crossing (ISC), (ii) symmetry-breaking chargeseparation (SBCS),70,71 and (iii) singlet fission (SF). AmongFigure 7. (a) Femtosecond transient absorption spectra (fs-TAS) of TIPS-Hep film under air irradiated at 740 nm, 0.70 μJ. (b) Fitting curves at514, 620, and 815 nm after the irradiation obtained by the target analysis. (c) Species-associated spectra and (d) time-dependent populationdynamics of S1, TT, and T1 + T1 states.Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116007https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.5c14689?fig=fig7&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asthese, the possibility of SBCS can be excluded, as no radicalcation/anion signals characteristic of charge-separated specieswere detected in the fs-TAS spectra, unlike in previouslyreported systems.72 Therefore, the accelerated triplet for-mation in the TIPS-Hep films is most likely attributed toenhanced ISC and/or SF processes.To evaluate whether the sequential SF model provides anappropriate description of the excited-state dynamics, wecompared it with three alternative kinetic models: (i) a three-component multiexponential fit, (ii) a model involving onlyISC, and (iii) a model incorporating two competing ISCpathways (Figures S25−S27). In all these cases, the fittingcurves were inconsistent with the experimentally observedtime-dependent behaviors, and species-associated spectra(SAS) failed to reproduce physically reasonable features.Therefore, we conclude that the sequential SF model mostaccurately represents the excited state relaxation process in thissystem (Figure 7).The global analysis (target analysis) using the sequentialmodel (Figure 6b) provided three independent spectra of eachS1, TT, and T1 + T1 species (Figure 7c), and time-dependentpopulation dynamics over time (Figure 7d). The three-component sequential relaxation process is different from thedynamics in solution (Figure 5), where only S1 and T1 wereobserved. The S1 and T1 + T1 spectra closely resemble those ofthe S1 and T1 in THF, as described above. In contrast, the TTspectrum obtained from the global analysis exhibits a shapesimilar to that of S1. Given the significant difference in molarabsorption coefficients between singlet and triplet states, thisresemblance can reasonably be similarity between theelectronic states in the TT state and the S1 state, whichinevitably causes the TT spectrum to appear closer in shape toS1. Another possible explanation is the presence of aheterogeneous molecular environment in the amorphous film(vide infra), where a small fraction of relatively long-lived S1state may persist.The rate constants determined from the global analysis areas follows: nonradiative decay from S1 to S0 (kNR″ > 1.1 × 1010s−1), singlet fission from S1 to TT (kSF = 1.4 × 1011 s−1), TTdissociation to T1 + T1 (kDISS = 1.5 × 109 s−1), and TTrecombination to the ground state (kREC = 1.0 × 1010 s−1).Notably, kSF (1.4 × 1011 s−1) is about 3 orders of magnitudegreater than kISC (2.8 × 108 s−1), indicating a substantialacceleration of the triplet formation in the thin film. Based onthe population ratios such as S1/TT and S1/(T1 + T1) from thetarget analysis, the quantum yields of TT and T1 generation(ΦSF and ΦT) were estimated to be 75% and 20%, respectively(Figure 7d). Considering that the maximum ΦSF and ΦTvalues are 100% and 200%, respectively, these results certainlydemonstrate the occurrence of SF. However, optimization of‘electronic coupling’ and ‘conformational flexibility’ associatedwith molecular orientation is essential for further efficiencyimprovements.73 The S1 quenching rate constant in film (1.5 ×1011 s−1) is also significantly faster than in solution (1.1 × 1010s−1), attributed to the SF process in the solid state. The XRDresults indicated that the thin film was amorphous, suggestingthat there were no strong interactions between TIPS-Hepmolecules in the film.Therefore, it was assumed that the molar absorptioncoefficient of TIPS-Hep was identical in the THF solutionand in the thin film. We then calculated ΦT using the followingmethod. When the transient spectra in THF and thin film arenormalized at the S1 absorption maximum, the ΔAbs values atthe T1 maximum are 0.00133 in THF solution and 0.0109 inthe film, respectively (Figure S28). Using the obtained tripletquantum yield (ΦISC) of TIPS-Hep in THF (2.4%) as areference, the triplet quantum yield (ΦT) in the film wasestimated to be (0.0109/0.00133) × 2.4 = 20%. This value(20%) is quantitatively reliable, even considering that bothmonomer-like and aggregated species with slightly differentdecay may coexist within the amorphous film. It is alsonoteworthy that this value is an order of magnitude greaterthan ΦISC in THF (∼2%), further supporting SF as thedominant triplet pathway.Regarding the ISC, the amorphous nature of the film, asconfirmed by XRD measurements, suggests that vibrationsuppression effects are minimal.15,70 Despite ΦSF = 75%, theΦT value (∼20%) is relatively low, which may be due to theshort lifetime of the TT state (20 ps), insufficient for spinconversion to yield two independent triplets. Taken togetherwith the absorption and XRD results, these results indicate thatthe bulky TIPS-ethynyl substituents at the 5,9,14,18-positionseffectively suppress strong aggregation of the heptacenebackbones in the solid state. This steric hindrance not onlyprevents the formation of detrimental excimers or dimers (asobserved in pristine heptacene) but also promotes a spatiallyisolated yet electronically coupled arrangement that facilitateSF from S1 + S0 to TT.Based on these results, we conclude that SF occurs in theTIPS-Hep film. To further examine the excitation-wavelengthdependent dynamics, fs-TAS measurements were performed at870 and 970 nm (Figures S29 and S30). The results wereconsistent across all excitation wavelengths, indicating that SFproceeds after nearly quantitative internal conversion from S2to S1. Even when the S1 state was directly excited at 970 nm,SF proceeds with dynamics similar to those observed under S2excitation, except for the absence of S2 → S1 relaxation.To further investigate the long-lived triplet states, ps-TASmeasurements of the TIPS-Hep film were conducted (FigureS31). The T1 lifetime was determined to be ∼0.95 μs (kT = 1.1× 106 s−1), significantly longer than those typically reported foracene films. This prolonged triplet lifetime is likely associatedwith the amorphous morphology discussed above. Moreover,no laser power dependence was observed in fs-TAS measure-ments between 0.45 to 3.45 μJ (Figure S32), supporting theamorphous nature of the film. The absence of laser-intensity-dependent quenching processes, such as singlet−singletannihilation, further indicates that molecular orientation andaggregation are minimal in the TIPS-Hep film.■ CONCLUSIONSIn this study, we successfully synthesized and characterized5,9,14,18-tetrakis(triisopropylsilylethynyl)heptacene (TIPS-Hep), a soluble and stable heptacene derivative. Pure TIPS-Hep was obtained through an in situ Strating−Zwanenburgreaction from its α-diketone precursor (TIPS-7DK), enablingdetailed photophysical analysis in both solution and thin-filmstates under ambient conditions.In deoxygenated THF at room temperature, TIPS-Hepexhibited monomeric properties with a weak absorption peakat 970 nm attributed to the dipole-forbidden S1 (21Ag) ← S0(11Ag) transition, the main absorption bands at 671, 737, and820 nm to the dipole-allowed S2 (11B2u) ← S0 (11Ag)transition, and the weak shoulder around 870 nm to anelectronic state in equilibrium with the ground state of TIPS-Hep. The fluorescence peaks were observed at 894 and 961Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. Soc. 2026, 148, 6000−60116008https://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.5c14689/suppl_file/ja5c14689_si_001.pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.5c14689?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asnm with a low fluorescence quantum yield (ΦFL′ = 0.02%) anda short fluorescence lifetime (<100 ps). The consistencybetween the vibronic progressions of the excitation andemission spectra (∼780 cm−1) strongly suggests that theemissive state is in equilibrium with the ground state of TIPS-Hep. From the transient absorption measurements, ISCquantum yield (ΦISC) was estimated to be 2.4 ± 0.8% togetherwith τT = ∼ 10 μs, with triplet formation proceeding viainternal conversion. The nonradiative decay from the S1 energywas dominant and no singlet fission was observed in thesolution phase.Conversely, in spin-coated thin films, TIPS-Hep showedfaster and enhanced formation of the triplet excited states.Since multiple excited species are involved in fs-TAS, severalkinetic models were analyzed, and a sequential SF model wasdetermined to be the most appropriate. The significantlyenhanced S1 quenching rate constant (5.1 × 1010 s−1) andglobal analysis with a sequential model identified the formationof triplet pairs (TT) and free triplets (T1) with respectiveyields of 75% and 20%. This is the first observation of singletfission using heptacene as far as we know. Importantly, thebulky TIPS-ethynyl substituents at the 5,9,14,18-positionseffectively suppress strong aggregation of the heptacenebackbone in the solid state, thereby minimizing unproductivedimerization while still allowing the favorable intermolecularinteractions necessary for efficient SF. These results enhancethe understanding of photophysical processes in extendedacenes. The study offers valuable guidelines for developingadvanced organic electronic devices.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/jacs.5c14689.Materials, instrumentation, analytical methods, syn-thesis, additional analytical data, theoretical caculation,and additional characterization data (PDF)■ AUTHOR INFORMATIONCorresponding AuthorsTakashi Hirose − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, Japan; orcid.org/0000-0002-5351-2101; Email: hirose@scl.kyoto-u.ac.jpTaku Hasobe − Department of Chemistry, Faculty of Scienceand Technology, Keio University, Yokohama, Kanagawa 223-8522, Japan; orcid.org/0000-0002-4728-9767;Email: hasobe@chem.keio.ac.jpHiroko Yamada − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, Japan; orcid.org/0000-0002-2138-5902; Email: hyamada@scl.kyoto-u.ac.jpAuthorsShinjiro Suzuki − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, JapanHayato Sakai − Department of Chemistry, Faculty of Scienceand Technology, Keio University, Yokohama, Kanagawa 223-8522, JapanMitsuaki Yamauchi − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, Japan; orcid.org/0000-0003-0005-5960Hironobu Hayashi − Center for Basic Research on Materials,National Institute for Materials Science (NIMS), Tsukuba,Ibaraki 305-0047, Japan; orcid.org/0000-0002-7872-3052Yoshiyuki Mizuhata − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, Japan; orcid.org/0000-0001-5301-0024Tatsuhisa Kato − Fukui Institute for Fundamental Chemistry,Kyoto University, Sakyo-ku, Kyoto 606-8103, JapanComplete contact information is available at:https://pubs.acs.org/10.1021/jacs.5c14689Author ContributionsThe manuscript was written through contributions of allauthors. All authors have given approval to the final version ofthe manuscript.FundingThis work was supported by Japan Society for the Promotionof Science (JSPS) KAKENHI (Grant Numbers JP25K01751 toH.Y., JP24K01473 to T.Hasobe, JP22K14556 to M.Y., andJP24K01576 to H.H.), the JSPS Bilateral Program(JPJSBP120243209 to H.Y.), Grant-in-Aids for TransformativeResearch Areas “Dynamic Exciton” (JP20H05833 to H.Y.) and“Material Science of Meso-Hierarchy” (JP23H04876 to T.Hasobe, JP24H01714 to M.Y., and JP24H01713 to T.Hirose),Nagase Science and Technology Foundation to H.Y., andTokyo Ohka Foundation for The Promotion of Science andTechnology to H.Y. Additional support was provided by theInternational Collaborative Research Program of Institute forChemical Research (ICR), Kyoto University. This work waspartially carried out through the joint research program of theMolecular Photoscience Research Center, Kobe University,and the Research Program of “Five-star Alliance” in “NJRCMater. & Dev”.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSThe authors are grateful to Dr. Kengo Suzuki, Hiromi Suzuki,and Takahiro Miyazaki, Hamamatsu Photonics K.K. for themeasurement of fluorescence lifetime. We also thank Dr.Nobutaka Shioya, Dr. Hiroshi Matsuda, Prof. Dr. TakeshiHasegawa, Institute of Chemical Research (ICR), KyotoUniversity, for XRD measurements. Additional support wasprovided by the Joint Usage/Research Center [JURC, ICR,Kyoto University] by providing access to a Bruker Avance III600 NMR spectrometer and a Bruker E500 spectrometerequipped with a super high Q resonator (ER 4122SHQ). Wealso acknowledge the SuperComputer System, ICR, KyotoUniversity for providing computation time.■ ABBREVIATIONSCH2Cl2 dichloromethaneLED light emitting diodeTD-DFT time-dependent density-functional theoryTHF tetrahydrofuranTLC thin layer chromatography.■ REFERENCES(1) Anthony, J. E. Functionalized Acenes and Heteroacenes forOrganic Electronics. Chem. Rev. 2006, 106, 5028−5048.Journal of the American Chemical Society pubs.acs.org/JACS Articlehttps://doi.org/10.1021/jacs.5c14689J. Am. Chem. 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