Thermochromic properties of quaterthiophene, an alkyl-substituted quaterthiophene derivative and its corresponding polymer

We report for the first time the thermochromic properties of a substituted oligothiophene. The temperature-dependent absorption spectra of 3′,4″-didecyl-2,2′:5′,2″:5″,2‴-quaterthiophene (DDQT) show the appearance of a red-shifted band that is caused by conformational changes. The changes in the optical properties of DDQT are compared with those observed in the unsubstituted quaterthiophene (QT). In the latter, a parallel type excitonic model is used to explain the changes in the optical spectra. The thermochromism of DDQT is also compared with that of the corresponding polymer (PDDQT). For all compounds, the fluorescence spectra also show a new red-shifted band. The origin of this new emission is discussed.