Configuration mixing upon reorganization of dihedral angle induces rapid intersystem crossing in organic photoredox catalyst

Abstract

A long excited state lifetime is a desirable quality of photocatalysts because it enables a higher probability of energy or electron transfer from the photocatalyst to a substrate.

Interrogation of O-ATRP Activation Conducted by Singlet and Triplet Excited States of Phenoxazine Photocatalysts

“…Certainly, high-yield long-lived triplet excited states are commonly desired in solution-phase photoredox catalysis 41 and can be engineered in organic systems without heavy atoms by exploiting molecular substructures with orthogonal π orbitals to increase spin-orbit coupling and promote intersystem crossing. [42][43][44][45][46] However, the predecessor singlet excited states often have lifetimes on the order of ones to tens of nanoseconds, which can be long enough to engage in bimolecular photochemistry as long as there is sufficient concentration of the reactive partner.…”

“…The second question, which is tied to Δ G ET 0 , has to do with whether the singlet or triplet excited state of the PC is the dominant reactant under synthetic conditions. Certainly, high-yield long-lived triplet excited states are commonly desired in solution-phase photoredox catalysis and can be engineered in organic systems without heavy atoms by exploiting molecular substructures with orthogonal π orbitals to increase the spin–orbit coupling and promote intersystem crossing. − However, the predecessor singlet excited states often have lifetimes on the order of ones to tens of nanoseconds, which can be long enough to engage in bimolecular photochemistry as long as there is sufficient concentration of the reactive partner. The third question involves intramolecular charge-transfer (CT) excited states and the observation that PCs possessing such states perform better in O-ATRP by the metrics of polymer dispersity and initiator efficiency.…”

Unified Framework for Photophysical Rate Calculations in TADF Molecules

“…In this sense, the role of the mixing of diabatic configurations has been proposed as an important mechanism associated with changes in the rates of ISC. 25,55 For the 4CzIPN molecule, great agreement is found between predicted and experimental ISC rates. The calculated rISC rate, however, is seen to underestimate the experimental value by 2 orders of magnitude.…”

“…This suggests that nonadiabatic effects are not necessary for efficient rISC as non-Condon effects may be more pronounced. In this sense, the role of the mixing of diabatic configurations has been proposed as an important mechanism associated with changes in the rates of ISC. , …”

Extension of molecules with an inverted singlet–triplet gap with conjugated branches to alter the oscillator strength

“…The superposition of all singly excited states was employed in lieu of a single configuration picture -for instance, a HOMO to LUMO excited state -to consider all singly excited configurations with appreciable weight in the wavefunction, which also can alter the DE ST from the exchange energy of orbitals, as shown in previous works. [42][43][44] Since each configuration has a different coupling strength with the DECs, the interaction with the DECs can also be more accurately accounted for. The DECs are classified into three categories according to the number of unpaired electrons as shown in Fig.…”