Asymmetric multibranched conjugated molecules: synthesis, structure and photophysical properties

The symmetric multibranched π-conjugated compounds with C3 or C6 configuration have been intensively studied. The reports on asymmetric multibranched compounds are very limited. In this work, we designed and synthesized two asymmetric multibranched π-conjugated molecules using truxene as the central core, diphenylamino and thiophenyl (or thiophenylethynyl) groups as the different branches respectively: 2,7-di(N,N-diphenylamino)-12-(2-thiophenyl)-5,5',10,10',15,15'-hexaethyltruxene and 2,7-di(N,N-diphenylamino)-12-(2-thiophenylethynyl)-5,5',10,10',15,15'-hexaethyltruxene. Their photophysical properties have been explored combining with their theoretical calculation and X-ray single-crystal structure of a key intermediate. Though their different π-conjugation length of branches, the two title compounds exhibit almost same absorption maxima. However, their emission peaks behave a gradual red-shift with the increase of the conjugation length. The theoretical calculation results indicate that the two asymmetric compounds behave a main transition from the HOMO-1 to the LUMO or from the HOMO to the LUMO+1 upon excited.