Steady-state and time-resolved fluorescence anisotropy of 2,9-di-n-pentyl-5,6,11,12-tetraazo-5,6,11,12-tetrahydrocoronene-5,6,11,1 2-tetracarboxy-bis-n-heptadecylimide

Abstract

The photophysical properties of 2,9-di-n-pentyl-5,6,11,12-tetraazo-5,6,11,12-tetrahydrocoronene-5,6,11,1 2-tetracarboxy- bis-n-heptadecylimide (P5-17) in solution are investigated as a function of concentration, In 2-methyltetrahydrofuran, above 2 X 10(-5) M, a new absorption band with a maximum at 688 nm is observed indicating the formation of an aggregate. Upon excitation in this absorption band, emission from the aggregate with a maximum at 710 nm is observed, This emission coincides with that of the liquid crystalline discotic phase. The rotational dynamics of P5-17 and its aggregate are investigated using steady-state fluorescence measurements and time-resolved fluorescence anisotropy. From. the global analysis of the polarised fluorescence decay traces, it is found that for both monomer and aggregate, the anisotropy decay can be described by a monoexponential decay law. The rotational correlation time for the monomer is linked over two excitation wavelengths corresponding to S-0 --> S-1 and S-0 --> S-n transitions. For the aggregate, the excitation and emission dipoles are perpendicular and a fast fluorescence depolarization was observed.