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Thermal‐ and Photo‐Induced Phase‐Transition Behaviors of a Tapered Dendritic Liquid Crystal with Photochromic Azobenzene Mesogens and a Bicyclic Chiral Center
Authors:Dae‐Yoon Kim  Sang‐A Lee  Yu‐Jin Choi  Dr Seok‐Ho Hwang  Dr Shiao‐Wei Kuo  Dr Changwoon Nah  Dr Myong‐Hoon Lee  Dr Kwang‐Un Jeong
Institution:1. Department of Polymer Nanoscience and Technology, Department of Flexible and Printable Electronics, Chonbuk National University, Jeongju 561‐756 (Korea), Fax: (+82)?63‐270‐2341;2. Department of Polymer Science and Engineering, Dankook University, Yongin 448‐701 (Korea);3. Department of Materials Science and Optoelectronic Engineering, National Sun Yat‐Sen University, Kaohsiung 804 (Taiwan)
Abstract:A ribbon‐shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ3DLC) was successfully synthesized and its major phase transitions were studied by using differential scanning calorimetry (DSC) and linear polarized optical microscopy (POM). Its ordered structures at different temperatures were further identified through structure‐sensitive diffraction techniques. Based on the experimental results, it was found that the AZ3DLC molecule exhibited the low‐ordered chiral smectic (Sm*) LC phase with 6.31 nm periodicity at a high‐temperature phase region. AZ3DLC showed the reversible photoisomerization in both organic solvents and nematic (N) LC media. As a chiral‐inducing agent, it exhibited a good solubility, a high helical‐twisting power, and a large change in the helical‐twisting power due to its photochemical isomerization in the commercially available N LC hosts. Therefore, we were able to reversibly “remote‐control” the colors in the whole visible region by finely tuning the helical pitch of the spontaneously formed helical superstructures.
Keywords:chirality  dendrimers  liquid crystals  phase transitions  photochromism
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