Ab initio and DFT study of the electronic structures and spectroscopic properties of pyrene ligands and their cyclometalated complexes

Two ligands 1-diphenylphosphinopyrene (1-PyP) (L₁), 1,6-bis(diphenylphosphino)-pyrene (1,6-PyP) (L₂) and their cyclometalated complexes [Pt(dppm)(1-PyP-H)]⁺ (1), [Pt ₂(dppm)₂(1,6-PyP-H₂)]²⁺ (dppm = bis(diphenylphosphino)methane (2), and [Pd(dppe)(1-PyP-H)⁺ (dppe = bis(diphenylphosphino)ethane) (3) are investigated theoretically to explore their electronic structures and spectroscopic properties. The ground- and excited-state structures are optimized by the density functional theory (DFT) and single-excitation configuration interaction method, respectively. At the time-dependent DFT (TDDFT) and B3LYP level, the absorption and emission spectra in solution are obtained. As revealed from the calculations, the lowest-energy absorptions of 1 and 3 are attributed to the mixing ligand-to-metal charge transfer (CT)/intraligand (IL)/ligand-to-ligand CT transitions, while that of 2 is attributed to the IL transition. The lowest-energy phosphorescent emissions of the cyclometalated complexes are attributed to coming from the ³ILCT transitions. With the increase of the spin-orbit coupling effect, the phosphorescence intensities and the emissions wavelength are correspondingly increased.