Theoretical investigations of the substituent effect on the absorption and emission properties for a series of platinum (II) complexes supported by tetradentate N2O2 chelates

摘要

The photophysical properties, which vary as R is varied, of a series of [Pt(N2O2)] complexes bearing bis(phenoxy)bipyridine auxiliaries with different substituents R = H (Pt-H) (1), 4,4-2NH(2) (Pt-NH2) (2), 4,4'-2tBu (Pt-tBu) (3), 4,4'-2CN (Pt-CN) (4), and 4,4'-2NO(2) (Pt-NO2) (5) are investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The solvent effects are discussed in CH2Cl2, CH3CN and CH3OH solutions, respectively, by polarizable continuum model (PCM). It is anticipated that compared with G-donor substituents, pi-acceptors have more dramatic effects on the electronic and optical properties in this series of complexes. Introduction of pi-electron withdrawing substituents on bipyridine ligand will benefit the LLCT (or MLCT) and prohibit the non-radiative pathways via d-d transitions by increasing the energy gap between the HOMO-LUMO and d-d transitions. The results also reveal that the lowest-energy excitations of all complexes show blue-shifts in the polarized solution and when the polarity of the solvent increases from CH2Cl2, CH3CN and CH3OH, the low-energy broad absorption band exhibit blue-shifts. The lowest-energy excitations and photoluminescence of all complexes are dominated by pi(phenoxy) -> pi*(bpy/NO2) (LLCT) excited state mixed with some energetically d pi (Pt) - pi*(bpy/NO2) (MLCT) transition. (c) 2006 Elsevier B.V. All rights reserved.