Theoretical Determination of Rate Constants from Excited States: Application to Benzophenone

A cost-effective method of theoretically predicting electronic-transition rate constants from the excited states of molecules is reported. This method is based on density functional theory calculations of electronic states and quantitative rate constant determination with the Fermi golden rule. The method is applied to the theoretical determination of the excited-state decay mechanism of photoexcited benzophenone, a representative molecule in photochemistry and biochemistry. Calculated rate constants for benzophenone are quantitatively consistent with experimental ones, which validates the reliability of our rate constant calculation. The calculated population kinetics indicate that S₁ → T₂ → T₁ → S₀ is the predominant decay pathway.

Correlated Triplet Pair Formation Activated by Geometry Relaxation in Directly Linked Tetracene Dimer (5,5'-Bitetracene)

Singlet fission (SF) materials have the potential to overcome the traditional external quantum efficiency limits of organic light-emitting diodes (OLEDs). In this study, we theoretically designed an intramolecular SF molecule, 5,5'-bitetracene (55BT), in which two tetracene units were directly connected through a C-C bond. Using quantum chemical calculation and the Fermi golden rule, we show that 55BT undergoes efficient SF induced by geometry relaxation in a locally excited singlet state, ¹(S₀S₁). Compared with another high-performing SF system, the tetracene dimer in the crystalline state, 55BT has advantages when used in doped systems owing to covalent bonding of the two tetracene units. This feature makes 55BT a promising candidate triplet sensitizer for near-infrared OLEDs.