TY - JOUR

T1 - Calculation and spectroscopic assignment of charge-transfer states in solid anthracene, tetracene and pentacene

AU - Bounds, P. J.

AU - Siebrand, W.

AU - Eisenstein, I.

AU - Munn, R. W.

AU - Petelenz, P.

PY - 1985/5/1

Y1 - 1985/5/1

N2 - The Fourier-transform method of calculating polarization energies is used to evaluate the energies of electron-hole pairs in anthracene, tetracene and pentacene crystals as a function of separation, r. Charge-quadrupole interactions are included which refine and extend previous calculations on anthracene. Detailed analysis of the long-range behaviour shows that the total electrostatic energy has the coulombic 1/r dependence, mediated by an apparent dielectric constant which depends on direction, varying more weakly than the dielectric tensor itself and in the opposite sense. The calculated charge-transfer (CT) energies determine the potential for the CT eigenstates of the crystal hamiltonian. Several methods to approximate these states are discussed and a generalization of the Merrifield-Choi model is adopted for their description. It is shown that the lowest CT state is split by electron-transfer interaction between translationally equivalent molecules in the unit cell. By combining the calculated electronic eigenvalues with the expected vibrational structure of the CT states, a satisfactory assignment is obtained for all CT bands observed by Sebastian, Weiser, Peter and Bassler in the electro-absorption spectra of anthracene, tetracene and pentacene. This assignment is shown to be in qualitative agreement with the observed intensity distributions. The results of this spectroscopic analysis are compared with observed yields of optically generated charge carriers produced by isothermal dissociation of CT states. The available experimental results are shown to be consistent with the assumption that this process involves direct optical population of both electronic and vibronic CT levels, the latter relaxing vibrationally before (or independent of) their diffusive dissociation.

AB - The Fourier-transform method of calculating polarization energies is used to evaluate the energies of electron-hole pairs in anthracene, tetracene and pentacene crystals as a function of separation, r. Charge-quadrupole interactions are included which refine and extend previous calculations on anthracene. Detailed analysis of the long-range behaviour shows that the total electrostatic energy has the coulombic 1/r dependence, mediated by an apparent dielectric constant which depends on direction, varying more weakly than the dielectric tensor itself and in the opposite sense. The calculated charge-transfer (CT) energies determine the potential for the CT eigenstates of the crystal hamiltonian. Several methods to approximate these states are discussed and a generalization of the Merrifield-Choi model is adopted for their description. It is shown that the lowest CT state is split by electron-transfer interaction between translationally equivalent molecules in the unit cell. By combining the calculated electronic eigenvalues with the expected vibrational structure of the CT states, a satisfactory assignment is obtained for all CT bands observed by Sebastian, Weiser, Peter and Bassler in the electro-absorption spectra of anthracene, tetracene and pentacene. This assignment is shown to be in qualitative agreement with the observed intensity distributions. The results of this spectroscopic analysis are compared with observed yields of optically generated charge carriers produced by isothermal dissociation of CT states. The available experimental results are shown to be consistent with the assumption that this process involves direct optical population of both electronic and vibronic CT levels, the latter relaxing vibrationally before (or independent of) their diffusive dissociation.

UR - http://www.scopus.com/inward/record.url?scp=0000552433&partnerID=8YFLogxK

U2 - 10.1016/0301-0104(85)80072-0

DO - 10.1016/0301-0104(85)80072-0

M3 - Article

AN - SCOPUS:0000552433

SN - 0301-0104

VL - 95

SP - 197

EP - 212

JO - Chemical Physics

JF - Chemical Physics

IS - 2

ER -