Fluorescence properties of p-quaterphenyl and p-quinquephenyl derivatives in liquid solvents

Abstract

Absorption, fluorescence and emission anisotropy spectra, as well as quantum yields and fluorescence decay times of p-quaterphenyl (PQP), 4,4‴-bis-(2-butyloctyloxy)-p-quaterphenyl (BBQ), 2,5,2″″,5″″-tetramethyl-p-quinquephenyl (TMI) and 3,5,3″″,5″″-tetra-t-butyl-p-quinquephenyl (QUI) were investigated in several nonpolar and polar solvents. It was found that high quantum yield is accompanied by a short (not exceeding 1 ns) lifetime and considerable emission anisotropy in low viscosity solvents. For TMI and QUI, which incorporate as many as 5 phenyl groups, the quantum yield in dioxane is 0.98 and 0.97, respectively. In the case of molecules with 4 phenyl groups, the quantum yield is slightly lower, amounting to 0.91. Rotational motions of terminal phenyl groups cause a lower deactivation of the excitation energy of the singlet state S1, the longer the linear molecule.