Liquid crystalline behavior and fluorescent property of calix[4]arene containing azobenzene photochromic group

Abstract

The reaction of 4&primer;-hydroxy-4-methyl azobenzene (1) and 1,6-dibromohexane afforded 6-bromo-1-((4- ((4-met hylphenyl)azo)phenyl)oxy)hexane (2), which further reacted with ρ-tert-butylcalix[4]arene to give the calix[4]arene derivative (3) whose lower rim had been modified by the azobenzene photochromic group. The structure of 3 was characterized by ¹H-nuclear magnetic resonance (NMR) and electrospray ionization-mass spectrometry (ESI-MS). The fluorescence intensity of compound 3 was two to four times higher than that of compounds 1 and 2 as the azobenzene group concentration in the range of 1.6×10^-5 to 8.0×10^-4 mol/L, indicating that the fluorescence quantum yield of the azobenzene group had been improved through being attached to the calix[4]arene skeleton. The liquid crystalline behavior of compound 3 was studied by polarized microscopy (POM) and differential scan calorimeter (DSC). Compound 3 exhibited the enchased texture of a smectic liquid crystal from 209.4?C to 219.5?C on heating, while 2 exhibited a liquid crystalline phase from 87.4 to 83.2?C on cooling. It was found that the calix[4]arene skeleton was a good platform for conformation immobilization of azobenzene photochromic group and the formation of liquid crystalline.

Keywords

azobenzene, calixarene, thermotropic liquid crystal, fluorescence