FLUORESCENCE EMISSION AND CONFORMATIONAL-CHANGES OF 1,3,5,7-TETRA-T-BUTYL-S-INDACENE (TTBI)

The electronic properties of 1,3,5,7-tetra-t-butyl-s-indacene (TTBI) i n the second excited singlet state have been studied by absorption and fluorescence spectroscopy. Fluorescence from S2 may be related, as in the azulene case, to the large energy gap between S2 and S1 and to th e high S0 --> S2 oscillator strength. Absorption, fluorescence excitat ion, and fluorescence spectra have been measured on rigid TTBI solutio ns at 77 K. Several emissions have been observed which have been assig ned to different conformers of TTBI. Photoselection data indicate that the symmetry of TTBI differs in the S2 state with respect to the grou nd state with minor structural changes.