Effect of pi-conjugated length of bridging ligand on the optoelectronic properties of platinum(II) dimers

We report a quantum-chemical study of the electronic and optical properties of several platinum(II) dimers, Pt(pip2NCN)]2(L)(2+) (pip2NCNH = 1,3-bis(piperidylmethyl)benzene, L represents the bridging ligands pyrazine, 4,4'-bipyridine, or trans-1,2-bis(4-pyridyl)ethylene). The theoretical calculations reveal that as the pi-conjugated length of bridging ligand increases, the energies of HOMOs and LUMOs, bonding energy of Pt-N bridge, and the largest absorption strength increase whereas the ionization potentials decrease. According to the inner reorganization energy and density of states, we presume the hole-transporting properties of these dimers is better than the electron-transporting, and their inner reorganization energies for hole transport are lower than that of 4,4'-bis(phenyl-m-tolylamino)biphenyl (TPD), a well-known hole-transporting material. These platinum(II) dimers, especially Pt(pip2NCN)]2(bpe)(2+), hold promise for use as a new kind of third-order nonlinear optical material, owing to their large third-order polarizabilty value and high transparency. Moreover, the optoelectronic properties of these complexes are easy to tailor by modifying the peripheral and central ligands. These theoretical results are beneficial to the design of new functional materials with excellent optoelectronic properties.