Elucidation of the intramolecular energy transfer process of 9,9-spirobifluorene via a measurement of the time-resolved fluorescence anisotropy

Abstract

The present study involves molecular dynamic studies of fluorescence relaxation and energy transfer of the electronically excited 9,9-spirobifluorene (SBFL) molecule. SBFL shows two fluorescence peaks, λ max = 312 and 323 nm, upon electronic excitation at 297 nm. The decay process of the 312-nm species in a, diethylether - isopentane - ethanol (5:5:2 v/v) solution at 77 K consists of a single channel having TF = 7.3 ns. At ambient temperature, no the fluorescence polarization is observed because the rate of intramolecular energy transfer is so slow in comparison with the molecular motion in the solvent. In glass at 77 K, however, a polarization of the fluorescence is cleanly observed. The energy transfer rate constant is derived to be (2.8 ± 0.4) × 10 7 s -1. Time-dependent density-functional theory calculations were performed to elucidate the electronically excited-state structures and energies.