Combined Theoretical and Experimental Study on Intramolecular Charge Transfer Processes in Star-Shaped Conjugated Molecules

In this work, 1,3,5-tristyrylbenzene (1) and 1,3,5-tristyryl-s-triazine (2) derivatives decorated with carbazole moieties have been synthesized for the first time. Their photophysical properties and the nature of their low-lying electronic excited state were investigated combining steady-state and time-resolved fluorescence spectroscopy, along with TD-DFT calculations. We found that the fluorescence emission of these compounds is highly sensitive to the polarity of the solvent, particularly for the s-triazine derivative whose color varies from blue to green or yellow depending on it. This behavior was associated with pronounced intramolecular charge transfer (ICT) processes from the periphery of the molecule to the π-conjugated core. These ICT processes involve large changes in the dipole moment and geometry, the latter especially localized in a single branch of the molecule and not along the entire π-conjugated core. The higher quantum yields determined for 1,3,5-tristyrylbenzene derivative (1) were associated with higher radiative decay rates. On the contrary, the smaller radiative decay rates determined for 1,3,5-tristyryl-s-triazine derivative (2) became comparable to the nonradiative decay rates