Photoluminescence of liquid-crystal azo derivatives in nanopores

摘要

The fluorescence of the nematic liquid crystal n-butyl-n'-methoxyazoxybenzene(BMAOB) in the form of a layer and in porous glasses with pores of different diameter is investigated. The fluorescence spectra of BMAOB in a layer and in small-diameter pores differ significantly from each other. A band peaked at 475 nm is observed in the stationary spectrum of a BMAOB layer, whereas the spectrum of BMAOB in pores smaller than 4 nm in diameter contains a band peaked at 550 nm. When the pore diameter decreases to I nm, the band at 475 nm is almost completely suppressed and only the band at 550 nm manifests itself. It is believed that the band at 550 run is due to the excimer luminescence of azo molecules. The fluorescence of a BMAOB layer indicates the occurrence of efficient trans-cis isomerization upon UV excitation. At the same time, another mechanism of phototransformation is dominant for BMAOB in porous matrices. Most likely, it is photodestruction caused by interaction of BMAOB molecules with oxygen and water bound in pores. Fluorescence of porous glasses is also revealed. Their fluorescence band shifts to shorter wavelengths with a decrease in the pore diameter. The fluorescence of porous glasses with filled pores is not detected, apparently, due to nonradiative energy transfer to BMAOB molecules. (C) 2004 MAIK "Nauka/Interperiodica".