Scenario of temperature-related variation of phosphorescence spectra of ortho-bromobenzophenone crystal

- Potential energy surfaces DFT calculated for 3 lower states of 2-BrBP molecule.
- Calculated energy of interaction of 2-BrBP molecule with its nearest neighbors.
- Phosphorescence and excitation spectra of 2-BrBP crystal from 4 to 300 K.
- Excitation spectra of 2BrBP crystal at 4 K.
- Scenario of changes in spectra of 2-BrBP with temperatures.

Luminescence and other properties of solid 2-bromobenzophenone demonstrate features, which require special attention. We present results, which include DFT calculations, integrated and time-resolved phosphorescence spectra, and excitation spectra. The energies of the title molecule were calculated for the S0, S1, and T1 states. Nanosecond time-resolved phosphorescence spectra were measured at three temperature points at which the spectra undergo substantial changes. Joint analysis of energy surfaces and experimental evidence allowed reconstruction of the emission scenario that determines temperature-related variations of spectra. Upon excitation to state S1 the molecule converges very fast to T1, emission from which can occur from the minima at 60° or at 180°. At low temperatures the molecule emits from the former, whereas at higher temperatures the molecule can overcome the barrier to emit from the lower minimum. The probability of excimer formation increases with increasing temperature.

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