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 1 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 2 with pronounced intramolecular charge transfer (ICT) processes from the periphery of the molecule to the pi-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 pi-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.