A TD-DFT study of the optical properties of (2,7-fluorene)-heterocyclic derivatives

The absorption and emission optical characteristics of nine models of (2,7-fluorene)-heterocyclic derivatives have been investigated at the B3LYP/6-311G(d,p)//TD-B3LYP/6-311G(d,p) level of theory. The obtained results reveal that the electronic excitations to the lowest singlet excited state of the studied models are dominated by the HOMO–LUMO electron transition. Among the nine models, the F(TQ)F species is predicted to be the easiest to excite, with excitation energy of only 1.91 eV. Among the all studied compounds the F(QX)F model displays the highest vertical singlet transition energy (2.90 eV).