PRESSURE-DEPENDENCE OF THE POLARIZED REFLECTANCE SPECTRUM OF A SOLID CHARGE-TRANSFER COMPLEX, PERYLENE-HEXACYANOBUTADIENE (HCBD)

The polarized reflectance spectrum of the perylene-HCBD complex has been measured al high pressures up to 26 kbar. Extraordinary intensity of the charge-transfer band is observed at high pressures, which cannot be reproduced by a conventional analytical model such as a dimer or trimer model. It is shown that this intensity can be naturally explained by applying the results of diagrammatic valence-bond calculations for an infinite-chain model, which has been reported by Painelli et al. [J. Chem. Phys. 87 (1987) 1705]. The degree of charge transfer-rho, the transfer integral t, and the site-energy difference from the donor to acceptor-DELTA at each pressure are estimated, and the pressure dependence of t and DELTA is found to be partial derivative ln t/partial derivative P = +2.9% kbar-1 and partial-derivative-DELTA/partial derivative P = -9.6 meV kbar-1, respectively.