Time-dependent density functional theory investigate the effect of arylacetylide chain length of cyclometalated Pt(II) complexes

Time-dependent density functional theory (TDDFT) method was used to investigate the effect of arylacetylide chain length on the geometrical structures, electronic properties, electroluminescent properties, absorption and emission spectra of four cyclometalated Pt(II) complexes [Pt(tBu)3(tpy){CC(C6H4CC)n−1}C6H5]+ (n = 1–4). The ωB97XD functional which includes long range corrections and empirical dispersion proved to be suitable for calculating the characters of the lowest singlet excited state (S1) and the lowest triplet excited state (T1) in TDDFT calculations. With the arylacetylide chain increasing, the energy levels of the occupied molecular orbitals could be raised orderly, while the unoccupied molecular orbitals had little changes. Moreover, both the absorption and emission wavelengths were red-shifted with the arylacetylide introduction. The difficulties of hole and electron injection gradually decreased. When there were four arylacetylide ligand, the complex had the best performance for electron and hole transport.

► The energy levels of occupied molecular orbitals could be raised orderly.
► The unoccupied molecular orbitals have little changes.
► The hole injection become harder while the electron injection become easier.