A Time-Dependent Density Functional Study of the Singlet−Triplet Energy Gap in Charge-Separated States of Rigid Bichromophoric Molecules

Abstract

Time-dependent density functional theory (TD-DFT) has been used to calculate gas-phase singlet−triplet energy gaps, ΔEST, for the charge-separated states of a series of donor−[bridge]−acceptor molecules, in which a dimethoxynaphthalene (DMN) donor and a dicyanovinyl (DCV) acceptor are connected by a rigid hydrocarbon (norbornylogous) bridge, ranging from four bonds to 13 bonds in length. Through the use of five different functionals, B3P86, B3LYP, B3PW91, BPW91, and BLYP, together with the 6-311G(d) basis set, it is found that TD-DFT theory gives a good description of the electron density distribution in the charge-separated (CS) states in that the calculated dipole moments of the CS states are in acceptable agreement with experimental data. The calculated ΔEST values for all members of the donor−[bridge]−acceptor series are positive (i.e., the singlet CS state lies higher in energy than the triplet CS state), and the distance dependence of ΔEST follows an exponential decay with increasing number, n, of b...