Thermoreversible helical fibers from photoreactive triphenylene-derived liquid crystals in liquid paraffin

Liquid crystalline triphenylene derivatives, TPC1(p)-n (n = 6, 12, 14, 16) were prepared using p-alkoxycinnamate as the [2+2] photo-cyclization site. TPC1(p)-n (n = 12, 14, 16) showed Col(r) phase and gave crescent-shaped or helical fibers after UV-irradiated in liquid paraffin solutions at 90 and 110 °C in the Col(r) temperature range. The apparent photoreaction products were shown to be thermally reversible, i.e. they dissolved in liquid paraffin at high temperatures and reappeared on cooling, indicating that they were aggregates of oligomerized TPC1(p)-n. The reaction mechanism was discussed in terms of the structure of the liquid crystalline phase.