Steady-state spectroscopic and fluorescence lifetime measurements of new two-photon absorbing fluorene derivatives

Steady-state excitation anisotropy, lifetimes, and time-resolved emission spectra of new 2-photon absorbing fluorene derivatives were measured in aprotic solvents at room temperature. Excitation anisotropy spectra in viscous silicon oil allowed the determination of the spectral position of three electronic transitions S-0 --> S-1, S-0 --> S-2, S-0 --> S-3 (S-i, i = 1, 2, 3 are the singlet electronic states) and the angles (approximate to 30degrees) between absorption S-0 --> S-1 and emission S-1 --> S-0 dipole moments for the first electronic transition. Solvate relaxation processes in the first excited state of the investigated fluorene molecules affect the lifetimes of these states, tau(1), so that experimental values Of tau(1) do not correspond to those calculated by Strickler and Berg theory. The influence of the molecular concentration on the fluorescence quantum yields and tau(1) have been investigated.