Global and Target Analysis of Time-Resolved Fluorescence Spectra of Di-9H-fluoren-9-yldimethylsilane:  Dynamics and Energetics for Intramolecular Excimer Formation

Dynamics and energetics for intramolecular excimer formation of a diarylsilane, di-9H-fluoren-9-yldimethylsilane (DFYDMS) have been investigated by means of ps time-resolved fluorescence spectroscopy and ab initio calculation. Multiple fluorescence decay curves were globally deconvolved to generate time-resolved fluorescence spectra and decay-associated spectra (DAS), from which species-associated spectra (SAS) were obtained. It is shown in the global analysis that there are at least three excited states: Two states are the locally excited (LE) states (λmax ∼ 320 nm) having lifetimes of 0.70 ± 0.04 and 1.75 ± 0.02 ns, and another is the excimer state (λmax ∼ 400 nm) having a lifetime of 7.34 ± 0.02 ns. The species which decays with 0.70 ns evolves into a species with a red-shifted spectrum, which in turn decays in 7.34 ns. The experimental and ab initio results indicate that the rise time of 0.70 ns corresponds to the conversion of the initial S1 LE state having a near sandwich geometry to the S1 excimer state adopting a true sandwich geometry.