Pt(II) diimine complexes bearing varied alkyl chains: Synthesis, tunable photophysical properties and aggregation-induced optical power limiting enhancement

A series of Pt(II) diimine complexes with varied alkyl chains on 2,2′- dipyridyl ligands (Pt-C1–Pt-C3) have been synthesized and characterized. The photophysical properties and nonlinear absorption properties were elucidated using UV–vis absorption, emission and transient absorption spectroscopy, density functional theory (DFT) calculations and electrochemical experiments. It was found that increasing the alkyl chain led to regular changes in the photophysical properties of Pt-C1–Pt-C3. The original conjugated skeleton of the Pt(II) complexes were affected when the alkyl chain was introduced and extended. All complexes exhibited an obvious aggregation-induced phosphorescence emission (AIPE) in a mixed solution comprised of tetrahydrofuran/water. The formation of nanoparticles in the aggregated state induced these complexes to exhibit different excited state properties. When the water content increased, the emission intensity increases 3 ∼ 13-flod and the excited state lifetime increased 98-flod due to the formation of Pt(II) complex nanoparticles. As a result, the optical power limiting (OPL) performance of these complexes was greatly improved. Based on the systematical investigation of nonlinear optical complexes in aggregated state, this work provided a theoretical basis for the development of new OPL materials. Furthermore, the Pt(II) complex nanoparticles will be more conducive to the potential application of OPL devices.