title: Tuning fluorescence lifetimes through changes in Herzberg-Teller activities: the case of triphenylene and its hexamethoxy-substituted derivative.
abstract: The fluorescence spectra of triphenylene (TP) and 2,3,6,7,10,11-hexamethoxy-triphenylene (HMTP) are measured in glass matrices, and the vibronic structure associated with the electronic spectra is simulated with the help of quantum chemically computed molecular parameters. Franck-Condon (FC) and Herzberg-Teller (HT) mechanisms are included. For excited-state calculations, both configuration interaction with single excitations (CIS) and time-dependent density functional theory (TDDFT) are employed. It is shown that the FC activity is associated with modes of similar shape and frequency in both molecules, while the HT-induced false origins with the largest activity are associated with rather different frequencies and normal coordinates as a result of the mixing and energy lowering of the low-lying allowed excited states in HMTP. The increased HT activity explains the reduced S(1) state lifetime in the substituted TP, in turn driven by the excited-state rearrangement occurring upon substitution of the TP core.
authors.affiliation: Dipartimento di Chimica G. Ciamician, Universita di Bologna, Via F. Selmi, 2, 40126 Bologna, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Di Donato
authors.forename: Davide
authors.initials: D
authors.lastname: Vanzo
authors.forename: Monica
authors.initials: M
authors.lastname: Semeraro
authors.forename: Alberto
authors.initials: A
authors.lastname: Credi
authors.forename: Fabrizia
authors.initials: F
authors.lastname: Negri