Crystal-to-crystal phase transition in [alpha]-quaterthiophene: An optical and structural study

A solid-solid transition occurring at 191 degree Celsius from [alpha]-4T/LT to [alpha]-4T/HT is demonstrated to obtain large and thick [alpha]-4T/4T/HT single crystals preserving the overall crystallinity of the starting [alpha]-4T/LT single crystals grown by the floating-drop technique. The result suggests that the method is useful to obtain large single crystals of the high temperature polymorph through a simple controlled heating treatment performed on solution-grown single crystals of the low temperature polydmorph.