All intramolecular singlet fission chromophores feature E(T2) < 2E(T1)

Gabby's (Guoying Yao) survey study on the relation between E(T1) and E(T2) of intramolecular singlet fission (iSF) chromophores has been accepted for publication on Photochem. Congratulations to Gabby! It is an invited article and hence the publication fee of this open-access journal has been waived. In this study, Gabby employed spin-flip time-dependent density functional theory (SF-TDDFT) method to calculate the energies of the lowest two triplet states of a collection of representative iSF chromophores. The results show that all the chromophores feature E(T2) 2E(T1), a criterion imposed on all SF chromophores, intramolecular or not, to prevent the T1T1 -> T2S0 triplet fusion. There is an intrinsic incompatibility for iSF chromophores between the requirement of having large diradical character and the requirement of E(T2) > 2E(T1). Despite the thermodynamics sink for the T1T1 -> T2S0 triplet fusion of iSF chromophores, the fusion is kinetically hindered, due to the T1 -> S0 intersystem crossing hidden under the veil of an internal conversion within the triplet manifold of the total electronic spin, as pointed out in another recent paper of our group.