Dual Emissive Mono- and Bis-alkynylpyridinium Pt(II) Complexes: Synthesis and Luminescent Properties

A series of bis- and monoalkynyl Pt­(II) complexes with 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy, 1–3), 1,10-phenantroline (phen, 4–6), 4,6-diphenyl-2,2′-bipyridine (ppbipy, 7–10), and alkynylpyridinium ligands were synthesized. “D−π–A” alkynylpyridinium compounds contain a methyl or mesitylene pyridinium acceptor group attached to the donor alkynyl site via various π-conjugated aromatic linkers. The variation of the π-linker in the alkynylpyridinium ligand allows one to tune the photophysical properties of the Pt­(II) complexes by modifying the electronic properties and intersystem charge transfer in the resulting organometallic “D−π–A” system. All Pt­(II) complexes obtained demonstrate complicated emission behavior in solution, namely dual fluorescent/phosphorescent emission. At the same time, no aggregation at high concentration in solution and in the solid phase was detected. TDDFT calculations show that the transitions related to emission of the complexes 1–10 are strongly associated with the hybrid MLCT/ILCT charge transfer inside the {Pt–CC–R} unit, thus demonstrating that the complex molecule acts as a unified “D−π–A” system.