TITLE:
Structure, Photochromism and Liquid Crystal Properties of 1-Alkyl-2-(Arylazo)Imidazoles (Raai-CnH2n+1, n (Even) = 10 - 22)
AUTHORS:
Avijit Nandi, Chandana Sen, Debashis Mallick, Randhir K. Sinha, Chittaranjan Sinha
KEYWORDS:
Arylazoimidazoles; Structure; Photochromism; Liquid Crystal; Nematic-Isotropic Phase Transition; Smectic Phase
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.3 No.2,
June
5,
2013
ABSTRACT: Photochromism is the reversible structural
change of the molecules upon light irradiation having different spectral pattern before and after irradiation. Liquid crystal (LC) is a long-range
orientational order of the molecules in between solid and isotropic liquid
phases which share the properties of the crystal and liquid phases.
1-Alkyl-2-(ary-lazo)imidazoles, (Raai-CnH2n+1, R =
H, Me and n = 10, 12, 14, 16, 18, 20, 22) exhibits photochromism and two of
them (Haai-C18H37 and Haai-C22H45)
show Liquid crystal (LC) properties. One of these compounds, Meaai-C16H33 is
structurally characterized by single crystal X-ray diffraction study. The
compounds upon irradiation with UV light show E-to-Z isomerisation. Quantum
yields (φE→Z) of E-to-Z
isomerisation vary with the molar mass of the compounds. The reverse
transformation, Z-to-E, is recorded in thermal condition. The activation energy
(Ea) of isomerisation is determined by the controlled temperature
reaction. Liquid crystal property of the molecules is examined by polarizing
optical microscopy (POM) and DSC. The carbon chain length n = 18 shows nematic
(N)-isotropic (I) phase transition and an unknown Smectic (Sm) phase is
observed with n = 22 on heating cycle.