Investigating the influence of substituent groups in TTM based radicals for the excitation process: a theoretical study.

Tri-(2,4,6-trichlorophenyl)methyl (TTM) based radicals can be promising in providing relatively high fluorescence quantum efficiency. In this study, we have evaluated the photoluminescence properties of a series of TTM-based radicals by means of DFT and TD-DFT methods. The optimized structures of the ground states (D) and the first excited states (D) of all the radicals are calculated and the computed emission bands are comparable with previous experimental results. is determined from transition dipole moments () and the energy gaps between D and D (Δ), both of which can be regulated by the conjugated structures from the substituent groups. was derived from the mode-averaging method and is consistent with the experimental results. Factors influencing and , including the potential energy differences (Δ), the vibrational reorganization energies () and the electron coupling term (), are discussed. By comparing and in solvents with different polarities (cyclohexane, toluene, and chloroform), TTM based radicals in cyclohexane exhibit the most promising fluorescence efficiencies. Besides, two substituted radicals, namely 2Br-TTM-3PCz and 2F-TTM-3PCz, have been fabricated. The results show that fluorine atoms are able to increase Δ and a considerably small has been predicted. We expect that our calculation can benefit the design of light-emitting molecules in further experiments.