Author(s)

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.

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.

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

A. Nandi, C. Sen, D. Mallick, R. Sinha and C. Sinha, "Structure, Photochromism and Liquid Crystal Properties of 1-Alkyl-2-(Arylazo)Imidazoles (Raai-C_nH_2n+1, n (Even) = 10 - 22)," Advances in Materials Physics and Chemistry, Vol. 3 No. 2, 2013, pp. 133-145. doi: 10.4236/ampc.2013.32019.