The photophysics of all-trans polyenes from ttbP5, a nonphotolabile pentaene

The all-trans pentaene, 3,12-di(tert-butyl)-2,2,13,13-tetramethyl-3,5,7,9,11-tetradecapentaene (ttbP5) fluoresces in two different regions of the visible spectrum. It produces an extremely weak emission in the gas phase that can also be detected in the condensed phase; such an emission exhibits a negligible Stokes shift with respect to the 1Ag-->1Bu absorption transition and can in principle be assigned to the 1Bu-->1Ag emission of the compound. ttbP5 also exhibits a second fluorescence emission at approximately 520 nm in both the gas phase and the condensed phase. The emission in the condensed phase increases in strength and structure, with no change in spectral position, as the solvent viscosity increases by effect of the solution temperature being lowered. The spectral behavior of this pentaene (ttbP5) is different enough from that reported [J. Catalan et al., J. Chem. Phys. 128, 104504 (2008)] for its tetraene counterpart (ttbP4) to warrant a separate analysis in order to facilitate a better understanding of the way the photophysics of these polyenes changes as their chain is lengthened.