Spin-vibronic coupling induced intersystem crossing in tetraphenylporphyrin: Relevance in the photosensitization of prolycopene

We theoretically investigate the underlying mechanistic details of relaxation dynamics associated with the low-lying singlet and triplet states of meso-tetraphenylporphyrin (TPP). Quantum wavepacket dynamics reveal ultrafast internal conversion in the respective manifolds. The symmetry breaking of triplet excited states by vibronic coupling would facilitate a favorable intersystem crossing. Computed intersystem crossing rates within the spin-vibronic coupling mechanism compare well with the previous reports. Finally, we analyze the recent findings of Vijayalakshmi et al. (2015) (K. Vijayalakshmi, A. Jha, J. Dasgupta, Ultrafast triplet generation and its sensitization drives efficient photoisomerization of tetra-cis-lycopene to all-trans-lycopene, J. Phys. Chem. B 119 (28) (2015) 8669–8678, PMID:26065440) on the triplet sensitization of prolycopene to lycopene isomerization in the presence of TPP. [Display omitted] •Photosensitization efficiency of tetraphenylporphyrin (TPP) is explored.•Intersystem crossing rates of tetraphenylporphyrin (TPP) are explained by spin-vibronic coupling.•Vibronic coupling in the triplet states lead to ultrafast internal conversion.•Energy transfer from T1 of TPP to prolycopene enhances the isomerization quantum yield.