Abstract
Novel type of polyethylene imine having methoxy (–OCH3) substituent azobenzene side chain group through eight methylene spacer group (PEI8M) was successfully synthesized and characterized by the polymer by 1H NMR, differential scanning calorimetry, polarized optical microscopic and X-ray diffraction analysis. Synthesized polymer possessed liquid crystalline (LC) properties. Spin coated PEI8M film showed out-of-plane molecular orientation on annealing and non-polarized visible light irradiation. PEI8M in solid film exhibited photoresponsive properties upon irradiation of UV and visible light. PEI8M film also exhibited reversible molecular orientation from random state to out-of-plane and from out-of-plane to random state on annealing, non-polarized UV and visible light irradiation.
Highlights
In recent years, azobenzene containing polymers have attracted considerable attention for the possibility of changing the molecular orientation by irradiation with an appropriate wavelength of light, and the potential applications including reversible optical storage, holographic grating and optical switching [1,2]
In literature so far very few papers are published on spontaneous out-of-plane molecular orientation of polymeric liquid crystals (PLCs) [3,4,5,6,7]
Bobrovsky group reported that polyacrylate copolymer containing 4-ethoxy4’-hexoxyazobenzene and cholesterol groups as side chains showed spontaneous out-of-plane molecular orientation on a glass substrate by annealing at 75 ̊C, whereas only partial out-of-plane molecular orientation was observed for polyacrylate homopolymer [3]
Summary
Azobenzene containing polymers have attracted considerable attention for the possibility of changing the molecular orientation by irradiation with an appropriate wavelength of light, and the potential applications including reversible optical storage, holographic grating and optical switching [1,2]. The azobenzene derivatives are known to undergo trans/cis photoisomerization upon irradiation This is not a simple switching process between the two photochromic isomers, because a steady state is strongly dependent on the substitution and the wavelength of the excitation. Our group reported that PEI having nitro substituent azobenzene side chain group showed out-of-plane molecular orientation on a glass substrate by annealing but not upon non-polarized visible light irradiation [8]. Ujiie group reported that some polyethylene imines (PEIs) having azobenzene groups as side groups show liquid crystalline phases and align perpendicular direction to the substrate spontaneously by heating and following cooling without any alignment process [9,10]. We demonstrated the multiple reorientations of the azobenzene chromophores in PEI8M
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