Predicting Excited-State and Luminescence Properties of a Cyclometalated Iridium(III) Complex: Quantum Mechanics/Molecular Mechanics Study

The excited-state and luminescence properties of a cyclometalated Ir(III) complex with two (CN)-N-boolean AND ligands ((CN)-N-boolean AND = 2-(2-4-difluorophenyl)pyridine, F(2)ppy) and one acyclic diamino carbene (ADC) ancillary ligand have been investigated by employing computational chemistry methods. We also considered the environmental effects on excited-state properties in CH2Cl2 solution and crystal. The less overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) can reduce the energy gap Delta E-ST between the lowest excited singlet and triplet states. The calculated fluorescence emission peak (S-1 -> S-0) matches with the experimental values in two media. The small Delta E-ST and proper spin-orbit coupling matrix elements (SOCMEs) facilitate the reverse intersystem crossing (rISC) processes from T-1 to S-1 states. Moreover, the forward ISC process takes precedence over transient fluorescence emission and reverse ISC process is also faster than the corresponding phosphorescence emission. This effect may be observed both in the dichloromethane solution and in crystal. By absorbing thermal energy, the excitons of T-1 states upconvert to S-1 states and then radiate energy from S1 states. As a consequence, this Ir complex displays typical characteristics of thermally activated delayed fluorescence (TADF) emitters, and it promises to be the first example of Ir complex with TADF.

Automated summary

The excited-state and luminescence properties of a cyclometalated Ir(III) complex with unique ligands were investigated using computational chemistry methods. The study revealed the distinct fluorescence emission characteristics and rapid reverse intersystem crossing process of the complex.