Time-resolved Study on Unconventional Fluorescence of an Azobenzene Liquid Crystal and its Phase Transition

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Abstract
Fluorescence properties of azobenzene liquid crystal, 4,4′-dioctyloxy- azobenzene, were examined by steady-state and picosecond single-photon timing spectroscopy. It was found that the fluorescence from azobenzene aggregate with a peak at ∼ 630 nm was observed in the solid phase in addition to the very weak S2 fluorescence from azobenzene monomer centered at 420 nm. The fluorescence lifetimes of both aggregate and monomer S2 state were estimated to be approximately 150 ps and shorter than 2 ps. The relationship between the excited-state dynamics of azobenzene liquid crystal and its phase transition was analyzed on the basis of the temperature dependence of relative fluorescence intensity and fluorescence lifetime of aggregate.