Thermochemical studies of twist-twist pi conjugated, sterically crowded stilbenes using simultaneous TG-DTA

The thermal transformations of three twist-twist pi conjugated, sterically crowded stilbenes were monitored using simultaneous TG-DTA with a rising te mperature program. The simplest compound, di-tert-butylstilbene, 1, was sho wn to melt and then completely evaporate. Compound 2, an extended version o f 1 with three rings, melted and then partially evaporated, forming an inte rmediate, which evaporated at a higher temperature. An endothermic peak was observed in both 1 and 2 prior to the main melting point. This peak corres ponds to a solid/solid or solid/liquid crystal phase transition. Compound 3 , an extended version of 1 with four rings, completely sublimed. The activa tion energies and frequency factors were calculated for evaporation or subl imation, using the Arrhenius method. (C) 1999 Elsevier Science B.V. All rig hts reserved.