Charge-transfer complexes of discogenic molecules : a time-resolved study based on Kerr ellipsometry

Charge-transfer complexes formed by a discogenic electron donor (2,3,6,7,10,11-hexa-n-pentyloxytriphenylene) and a non-discogenic electron acceptor (2,4,7-trinitrofluoren-9-one) in non-polar solvents are studied by picosecond time-resolved absorption spectroscopy based on Kerr ellipsometry. The transient spectra obtained following laser excitation either in the charge-transfer band or in the lower lying local acceptor band correspond to the oxidized donor and reduced acceptor. Recombination of the geminate ion pair occurs with a first order rate constant of 1.7 × 1010 s–1. It is shown that the polarization of the transient species absorption is orthogonal to the charge-transfer transition. It is also demonstrated that the relative orientation between the donor and the acceptor in the geminate ion pair is not random.