Structure, Photochromism and Liquid Crystal Properties of 1-Alkyl-2-(Arylazo)Imidazoles (Raai-C_nH_2n+1, n (Even) = 10 - 22)

Avijit Nandi, Chandana Sen, Debashis Mallick, Randhir K. Sinha, Chittaranjan Sinha

Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata, India.
Department of Chemistry, Mrinalini Datta Mahavidyapith, Birati, India.

DOI: 10.4236/ampc.2013.32019                

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-C_nH_2n+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 (φ_E→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 (E_a) 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.

Keywords

Arylazoimidazoles; Structure; Photochromism; Liquid Crystal; Nematic-Isotropic Phase Transition; Smectic Phase

Conflicts of Interest

The authors declare no conflicts of interest.

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