A crossover from rod-shaped to bent-shaped in symmetric isoflavone liquid crystal trimers exhibiting unusual mesomorphic behaviour

• Published in: Journal of materials chemistry Vol. 22; no. 22; pp. 11335 - 11339
• Main Authors: Chan, Tze-Nee, Yeap, Guan-Yeow, Yam, Wan-Sinn, Madrak, Karolina, Zep, Anna, Pociecha, Damian, Gorecka, Ewa
• Format: Journal Article
• Language: English
• Published: 01.01.2012
• Subjects: Differential scanning calorimetry; Diffraction; Homology; Liquid crystals; Methylene; Phase transformations; Spacers; Trimers
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/c2jm30943b

A new series of symmetric isoflavone-based liquid crystalline trimers, 1,3-bis{[3-(4′-decyloxyphenyl)-4 H -1-benzopyran-4-one-7-oxy]alkyloxy}benzenes with 3-12 methylene units in both lateral spacers have been synthesized and characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. As expected, the phase transition temperatures strongly alternate as the number of methylene units in the spacers changes. An unusual mesomorphic behaviour was observed wherein short and long trimers exhibited smectic A (SmA) and/or smectic C (SmC) phase(s) while homologues with intermediate spacer length were purely nematogenic (N) in a broad temperature range. Formation and stabilization of the uniaxial nematic phase is caused by change of molecular geometry from rod-shaped for short homologues to strongly bent-shaped for long homologues. A new series of symmetric isoflavone-based liquid crystalline trimers, with 3-12 methylene units in both lateral spacers have been synthesized and characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction.