Accurate & cheap calculations of the lowest triplet state energy: an experimentalist's guide

Abstract

Triplet–triplet annihilation and singlet fission are bimolecular processes which can be exploited in a range of technological applications. These processes involve the first excited singlet and triplet states (S₁ and T₁), and have restrictions on their relative energies. While singlet–singlet energy differences are easily measured using optical spectroscopy, the singlet–triplet energy gap is less amenable to experiment. We report a computationally inexpensive method for the calculation of the energy of the lowest singlet–triplet transition for a range of extended π chromophores. Excellent correlation (mean absolute displacement ≲0.05 eV) between experiment and calculation is achieved for a wide range of molecules without requiring zero point energy calculations. This provides the experimental chemist with the necessary tools to accurately predict T₁ energies for novel molecules that are candidates for triplet–triplet annihilation or singlet fission.