Alkyl-substituted bipyridyl platinum (II) complexes bearing alkynyl-naphthalimide ligands: Synthesis, photophysical properties, and tunable aggregation-induced emission activity

Different alkyl chains were introduced into alkynyl-naphthalimide ligands and bipyridine ligands to synthesize five platinum complexes, their structures were characterized and the photophysical properties were systematically investigated. It was found that the introduction of alkyl chains had no obvious effect on the absorption and emission of these complexes in dilute solution, while influence aggregation-induced emission activity in aggregated state. In the mixed solvent system of tetrahydrofuran and ethylene glycol, the shorter alkyl chains on the bipyridine ligands strengthen the aggregation-induced phosphorescence emission (AIPE) properties of complexes, however, the introduction of different alkyl chains on the alkynyl-naphthalimide ligands makes no difference on their AIPE properties. Combining the single crystal results and Hirshfled surface analysis, the photophysical properties of these complexes in aggregated state were affected by the stacking modes, which is due to the different interactions. This research may broaden the scope for the design of multi-functional materials adopting different aggregation states.