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Mikaru Masuda, Joel Hao Jorolan, [Hironobu Hayashi](https://orcid.org/0000-0002-7872-3052), [Hiroko Yamada](https://orcid.org/0000-0002-2138-5902), [Tomoaki Miura](https://orcid.org/0000-0002-7281-3049), [Tadaaki Ikoma](https://orcid.org/0000-0003-2003-6839)

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[Excited Triplet Stateof Heptacene Studied by ElectronSpin Resonance](https://mdr.nims.go.jp/datasets/99710249-c512-4957-af44-42927c4209a5)

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Excited Triplet State of Heptacene Studied by Electron SpinResonanceMikaru Masuda, Joel Hao Jorolan, Hironobu Hayashi, Hiroko Yamada, Tomoaki Miura,and Tadaaki Ikoma*Cite This: J. Am. Chem. Soc. 2026, 148, 36309−36313 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: Excited triplet states of acene (3nA*, n being the number of benzene rings) have recently attracted considerableattention because of their useful applications. However, 3nA* with n > 5 have not been experimentally explored, due to theinsolubility and instability of the higher acenes. In this study, we succeeded in detecting spin-polarized 37A* by combining thephotoprecursor method using a degassed amorphous matrix of o-terphenyl and time-resolved electron spin resonance. 37A* is thelongest acene among the 3nA* observed to date. It has been clarified that 37A* is generated by preferential intersystem crossing tothe in-plane sublevels and possesses zero-field splitting constants of D = 0.035 cm−1 and E = 0.000 cm−1. The D values for 3nA* (n =2−7) were found to follow a linear 1/n-dependence, expressed as D(n)=0.180/n+0.011 [cm−1], which provides a quantitative basisfor the spatial extent of excitation in even higher 3nA* states.Acene (nA), in which n benzene rings are linearly fused asillustrated in Scheme 1a, is a core molecule in thechemistry of various aromatics1−3 and is a central buildingblock for organic semiconductors.4,5Varying n allows tuning of the HOMO−LUMO energy gapof nA.6,7 Light absorption arising from the narrowed HOMO−LUMO gap enables excited-state chemistry applicable to solarenergy utilization, phototherapy, quantum information pro-cessing and optoelectronics. Photochemistry often proceedsfrom the excited triplet state, 3nA*, which is typically bornfrom excited singlet state, 1nA*, via intersystem crossing (isc),because its lifetime is longer than that of 1nA*.8 Recently 35A*has attracted attention as a molecule exhibiting MASERemission at room temperature,9,10 a quantum-entanglementstate involving many nuclear spin qubits of the hydrogensbonded to carbons.11−13 35A* and its derivatives are alsoutilized as sources of spin angular momentum at roomtemperature in dynamic nuclear polarization enhancing NMRsensitivity.14,15 Assemblies of nA with n ≥ 4 are expected toundergo singlet fission,16,17 which may enable surpassing thetheoretical limit of solar-energy conversion efficiency.18,19Thus, clarifying the electronic structure and dynamics of3nA* is an urgent and important issue in photochemistry andexciton engineering. In this paper, we performed electron spinresonance (ESR) measurements on 37A* photogenerated fromthe precursor, 7A-dk (Scheme 1b), to obtain the magnetic andkinetic properties of the spin-sublevels for higher 3nA* with n> 5, for which no experimental studies have been reported todate.Absorption spectra for 7A-dk and 5A-dk in degassed o-terphenyl (OTP), whose detailed preparation procedure isdescribed in section S1 of Supporting Information (SI), areshown in Figure 1. When the nπ* band of the dicarbonylgroup20 was excited in the wavelength (λ) range of 400−500nm using intense light for the decarbonylation (λdc), the nπ*bands decreased in intensity and several new bands appeared.The light-induced spectrum peaking at λ = 636, 689, 763, and795 nm for 7A-dk (Figure 1a), which is almost identical to thatfor 7A,21,22 demonstrates that 7A is produced from 7A-dk inOTP at room temperature. Since 7A exhibits severalabsorption peaks in the 400−500 nm region, the two peaksat λ = 427 and 452 nm, which overlap with the bleached nπ*band are attributed to 7A. Additional weak doublet in the530−600 nm region suggests the formation of byproducts. Onthe other hand, blue-light irradiation of 5A-dk induces aReceived: March 24, 2026Revised: August 16, 2026Accepted: August 18, 2026Published: August 24, 2026Scheme 1. (a) Molecular Structure, Molecular Axis System,And Point Group of Acenes (nA); (b) Photodecarbonyl-ation Reaction of 5A- and 7A-Diketones (5A-dk and 7A-dk)Communicationpubs.acs.org/JACS© 2026 The Authors. Published byAmerican Chemical Society36309https://doi.org/10.1021/jacs.6c06021J. Am. Chem. Soc. 2026, 148, 36309−36313This article is licensed under CC-BY-NC-ND 4.0Downloaded from pubs.​acs.​org/​jacsat/​article-pdf/​148/​34/​36309/​67390274/​jacs.​6c06021.​pdf by NATL INST FOR MATLS SCIENCE (NIMS) user on 06 October 2026https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Mikaru+Masuda"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Joel+Hao+Jorolan"&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="Hiroko+Yamada"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tomoaki+Miura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tadaaki+Ikoma"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tadaaki+Ikoma"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/jacs.6c06021&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/toc/jacsat/148/34?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/34?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/34?ref=pdfhttps://pubs.acs.org/toc/jacsat/148/34?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=sch1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=sch1&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/jacs.6c06021?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/spectrum with three peaks in the 500−650 nm region (Figure1b), assigned to 5A, indicating that 5A is generated from 5A-dk by blue-light irradiation at room temperature. The first twopeaks in the vibronic progression of absorption spectrum for5A in OTP agree with the doublet due to the byproduct of 7A-dk in OTP. This observation suggests the formation of abyproduct containing a 5A moiety (5A-bp), which issupported by ESR measurements (section S2 of SI). Thephotogenerated 7A and 5A in OTP were stable even underselective photoexcitation (section S3 of SI). We also performedthe same experiments using a degassed poly(methyl meth-acrylate) (PMMA) matrix and observed matrix-dependentphotostability of 7A and 5A (section S3 of SI).Figure 2 shows the transient ESR (trESR) spectra for 37A*and 35A*, detected at delay time (t) of 1.0 μs after the selectiveexcitation of the photogenerated 7A and 5A in degassed OTPat room temperature using the nanosecond lasers. Because thetrESR spectrum for 37A* at 80 K has a good signal-to-noiseratio, the spectrum at t = 0.4 μs is also superimposed in Figure2a. The intensity of ESR signal for 37A* linearly increases withthe incident laser power. The observed linear dependenceindicates that 37A* is generated by a one-photon process,excluding the possibility of two-photon excitation of 7A-dk orthe byproducts in OTP. Indeed, the total splitting of trESRspectrum of 37A* (ca. 78 mT) is much narrower than that of37A-dk* (ca. 140 mT), which was detected in OTP at 85 K(Figure S4). Both trESR spectra of 37A* and 35A* exhibitmicrowave emission on the low field side and absorption onthe high field side. The spectral pattern of 37A* resemblesthose of 35A* and small 3nA*. This similarity indicates that theupper spin-sublevels in 37A* are preferentially populatedthrough spin−orbit (SO) interaction with 17A*. Although thespectral phase could also be explained by rapid energy transferfrom an excited triplet state of nearby molecule with a similarenergy,23 the energy of 37A-dk* (2.36 eV) is much higher thanthat of 37A* (0.79 eV).20,24 Therefore, this mechanism oftriplet energy transfer can be ruled out for the observed spinpolarization of 37A*. The spectral width of 37A* is narrowerthan that of 35A*, reflecting the smaller zero-field splitting(zfs) among the spin-sublevels of 37A*. The observed spectrawere successfully simulated using the spin Hamiltonian(section S5 in SI) with the parameters listed in Table 1.The energies (εI) and splitting constants (D = −3εO/2 and|E/D| = |(εL − εS)/3εO)|) of the spin-sublevels (TI0) at zero-field as well as the population (pI0) of TI0 for 37A* and 35A*are plotted in Figure 3, together with those of 3ππ* states ofsmall nAs.25−31 The subscript I denotes the quantization axesparallel to the molecular axes (Scheme 1). Both the εL and εO,corresponding to the sublevels (TL0 and TO0) whose principalaxes are parallel to the long in-plane (L) axis and the out-of-plane (O) axis, respectively approach zero with increasing n. Incontrast, εS for the TS0 whose principal axis lies along the shortin-plane (S) axis, remains nearly constant, except for n = 1. Theobserved trend in εI is fully explained by the extension oftriplet excitation delocalized over the L-axis, which is thedirection of ring condensation. Because the zfs in 3nA* isdominated by the magnetic dipolar interaction between twoFigure 1. (a) Absorption spectrum (black) for 7A-dk doped indegassed OTP matrix, and difference spectrum (red) obtained afterirradiation with 9 mW light at λdc = 460−500 nm (light blue) for 39min at room temperature. The difference spectrum was obtained bysubtracting the preirradiation spectrum. (b) Absorption spectrum(black) for 5A-dk doped in degassed OTP matrix, and differencespectrum (green) after irradiation with 7 mW light at λdc = 470−500nm (light blue) for 39 min at room temperature. The spectrarecorded before blue-light irradiation (black) exhibit a broad offsetdue to light scattering.Figure 2. (a) TrESR spectra for 37A* measured at room temperatureat t = 1.0 μs (light red) and at 80 K at t = 0.4 μs (red) after thenanosecond laser flashes at λex = 640 (0.1 mJ/pulse) and 630 nm (0.4mJ/pulse), respectively, for the selective excitation of 7A in degassedOTP, which was prepared by the blue light irradiation at λdc = 450 nm(125 mW) for 4 min at room temperature. Inset indicates laser powerdependence of the ESR signal intensity for 37A* at 80 K measured atthe canonical field indicated by the red arrow. (b) TrESR spectrum of35A* measured at room temperature at t = 1.0 μs (green) after thenanosecond laser excitation at λex = 532 nm (0.8 mJ/pulse) for theselective excitation of 5A in degassed OTP, which was prepared bythe blue light irradiation at λdc = 450 nm (12 mW) for 90 min at roomtemperature. The black dashed curves represent simulationscalculated using the ESR parameters listed in Table 1.Table 1. g Factor, zfs Constants (D and E), NormalizedPopulation Differences (pI0), and Spin−Lattice RelaxationTime (T1)a for 37A* and 35A* in a Degassed OTP MatrixnA g D/cm−1 E/cm−1 pL0:pS0:pO0d T1/μs7Ab 2.005 0.035 0.0000 (1−0):(0−1):0 0.475Ac 2.002 0.045 −0.0015 0.41:0.59:0.00 1.9aSection S6 in SI. b80 K. cRoom temperature. dAssuming that the X-,Y-, and Z-axes are respectively parallel to the L-, S-, and O-axes likesmall 3nA* and that the smallest sublevel population, pO0, is zero.Journal of the American Chemical Society pubs.acs.org/JACS Communicationhttps://doi.org/10.1021/jacs.6c06021J. Am. Chem. Soc. 2026, 148, 36309−3631336310Downloaded from pubs.​acs.​org/​jacsat/​article-pdf/​148/​34/​36309/​67390274/​jacs.​6c06021.​pdf by NATL INST FOR MATLS SCIENCE (NIMS) user on 06 October 2026https://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.6c06021?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asunpaired electrons in π-orbitals,32 the εJ is expressed by eq 1with the integral of the molecular orbital for triplet excitation,ΨT.={ }gr jrgj rrJ j X x Y y Z z8( )38( )3( ): ( ), ( ), ( )Ja bcab ababa b0B2T2 25 T0B2,2 25(1)Here μ0, μB, r and j denote the permeability, the Bohrmagneton, the distance between the unpaired electrons, andthe component of r along the J-axis, respectively. Themolecular integral can be approximated by a summation ofthe atomic terms of the spin densities (ρ) on the a- and b-thatoms. In small 3nA*, the X-, Y- and Z-axes are assigned to theL-, S- and O-axes, respectively. The decrease of εL with n ismainly attributed to increase in the mean value of r caused bythe extension of triplet excitation. The decrease of |εO| with n isunderstood by a reduction in ρ associated with the excitationextension. In contrast, the nearly constant εS can be interpretedas the combined effect of two opposing factors, a decrease in ρand an increase in the number of atomic terms accompanyingthe excitation extension.The D-values for 3nA* of n = 2−7 lie well on the line ofD(n) = (0.180 ± 0.005)/n + (0.011 ± 0.002) [cm−1]. 31A* isexcluded from the fitting, because its symmetry is effectivelycloser to pseudo-D6h.25,33 A similar dependence of the D-valueon the π-conjugation length has been reported for the 3ππ*states of oligothiophenes34 and polyenals.35 The D-value, equalto −3εO/2, is proportional to ⟨r−3⟩ when ΨT is substantiallylocalized into two points, because the O-axis is parallel to theZ-axis, a principal axis with the largest splitting. Therefore, theobserved 1/n-proportionality of D in the 3ππ* state is likely toarise from the delocalization of triplet excitation. Also, similarlinear 1/n-relationship with a nonzero intercept has also beenreported for the HOMO−LUMO gap (Egap) of 1nA*.5,6 Asdiscussed in section S7 in SI, the 1/n-proportionality of D in3nA* of n = 2−13 can be understood through the analyticalsolution derived from a simple model assuming a uniform spindensity distribution over the peripheral carbons. To estimatethe spin distribution more accurately, we calculated it by thedensity functional theory (DFT) (section S8 in SI). Thecalculated distribution can be approximated as Gaussiandistributions, whose standard deviations are smaller than thetotal bond length between the terminal carbon atoms of thetwo edge rings along the L axis of nA. Linear 1/n-proportionalities of the spin-sublevel energies were obtainedeven in the Gaussian distribution, in which delocalization ofexcitation is restricted in the central rings (Figure S9).The preferential isc to the in-plane sublevels observed for37A* can be explained by the vibronic SO-interactionmediated by 1,3σπ* (or 1,3πσ*), analogous to the iscmechanism in small 3nA* (section S9 in SI). The g-value of37A*, which is larger than that of the free electron, may alsosuggest that SO-interaction contributes to the zfs (section S8in SI).■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/jacs.6c06021.Experimental details, TrESR spectra of byproductsphotogenerated from 7A-dk in OTP, photoreactivity ofdiketones and acenes in OTP and PMMA, TrESRspectrum of the T1 state for 7A-dk in OTP, simulationof TrESR spectrum, decay kinetics of the T1 states for7A and 5A in OTP, ring-number Dependence of the DValue, electronic structure and sublevel energies of 3nA*Calculated by DFT, and population rates of 3nA* (PDF)■ AUTHOR INFORMATIONCorresponding AuthorTadaaki Ikoma − Graduate School of Science and Technology,Niigata University, Niigata, Niigata 950-2181, Japan;Center for Coordination of Research Facilities, NiigataUniversity, Niigata, Niigata 950-2181, Japan; orcid.org/0000-0003-2003-6839; Email: ikoma@chem.sc.niigata-u.ac.jpAuthorsMikaru Masuda − Graduate School of Science andTechnology, Niigata University, Niigata, Niigata 950-2181,JapanJoel Hao Jorolan − Graduate School of Science andTechnology, Niigata University, Niigata, Niigata 950-2181,Japan; Present Address: Western Australia School ofMines, Faculty of Science and Engineering, CurtinUniversity, Kent Street, Bentley, Western Australia 6102,AustraliaHironobu Hayashi − Center for Basic Research on Materials,National Institute for Materials Science, Tsukuba, Ibaraki305-0047, Japan; orcid.org/0000-0002-7872-3052Hiroko Yamada − Institute for Chemical Research, KyotoUniversity, Uji, Kyoto 611-0011, Japan; orcid.org/0000-0002-2138-5902Tomoaki Miura − Graduate School of Science andTechnology, Niigata University, Niigata, Niigata 950-2181,Japan; orcid.org/0000-0002-7281-3049Complete contact information is available at:https://pubs.acs.org/10.1021/jacs.6c06021Figure 3. Dependence of the spin-sublevel energy (a) and the D-valueand orthorhombicity of zfs (b) on the π-conjugation size. Data of theopen symbols are taken from the literatures of 1A,25,26 2A,26,273A,28,29 4A,31 5A,30 while the filled symbols for 5A and 7A representdata obtained in this work. The solid straight lines in (a) and (b) arefitting curves. The inset in (a) shows the spin density distribution for37A* calculated by DFT.Journal of the American Chemical Society pubs.acs.org/JACS Communicationhttps://doi.org/10.1021/jacs.6c06021J. Am. Chem. Soc. 2026, 148, 36309−3631336311Downloaded from pubs.​acs.​org/​jacsat/​article-pdf/​148/​34/​36309/​67390274/​jacs.​6c06021.​pdf by NATL INST FOR MATLS SCIENCE (NIMS) user on 06 October 2026https://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?goto=supporting-infohttps://pubs.acs.org/doi/suppl/10.1021/jacs.6c06021/suppl_file/ja6c06021_si_001.pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tadaaki+Ikoma"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-2003-6839https://orcid.org/0000-0003-2003-6839mailto:ikoma@chem.sc.niigata-u.ac.jpmailto:ikoma@chem.sc.niigata-u.ac.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Mikaru+Masuda"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Joel+Hao+Jorolan"&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://orcid.org/0000-0002-7872-3052https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hiroko+Yamada"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-2138-5902https://orcid.org/0000-0002-2138-5902https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tomoaki+Miura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-7281-3049https://pubs.acs.org/doi/10.1021/jacs.6c06021?ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/jacs.6c06021?fig=fig3&ref=pdfpubs.acs.org/JACS?ref=pdfhttps://doi.org/10.1021/jacs.6c06021?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asAuthor ContributionsThe manuscript was written through contributions of allauthors.FundingFinancial support was provided by JSPS Kakenhi (23K17901)and research grants from Union Tool and TAKEUCHIScholarship Associations (to T.I.), and JST SPRINGJPMJSP2121 (to M.M.).NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTST.I. thanks Prof. Maeda and Prof. Nagashima (Saitama Univ.)for their kind help measuring ESR at QST. 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