DFT/TDDFT investigation on the electronic structures and photophysical properties of a series of substituted N-heterocyclic carbene (NHC) platinum(II) complexes

• Phosphorescence properties of five platinum(II) complexes have been investigated.
• Calculated lowest energy emission of 1 is agreement with the experimental value.
• Complex 3 has possibly the largest radiative decay rate value among these complexes.

The electronic and photophysical properties of a series of substituted N-heterocyclic carbene (NHC) platinum(II) complexes have been investigated by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The lowest-lying singlet absorptions for complexes 2–5 are attributed to the configurations of HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital). The emission energies for these complexes are obviously red-shifted in contrast to that of 1. For 3 and 4, the emission energies are nearly the same, consistent with their same energy gaps between of LUMO and HOMO. In addition, ionization potential (IP), electron affinities (EA) and reorganization energy (λ) also were obtained to evaluate the charge transfer and balance properties between hole and electron. From the calculated results, it can be seen that the complex 3 possesses possibly the largest kr value among these complexes due to the lowest ΔES1−T1, larger 3MLCT contribution, and higher μS1⁡ value. It is anticipated that this study could provide useful information for the synthesis of efficient platinum(II) phosphors in OLEDs.