Pt(II) diimine complexes bearing difluoro-boron-dipyrromethene acetylide ligands: Synthesis, photophysics, aggregation included emission and optical power limiting properties

A series of Pt(II) complexes bearing difluoro-boron-dipyrromethene (Bodipy) acetylide ligands and different alkyl/aryl substituted 2,2′-bipyridyl ligands (Pt-1 – Pt-3) were synthesized and characterized. Their photophysics, aggregation included emission (AIE) and optical power limiting properties were systematically investigated via UV−Vis absorption, emission, transient absorption, and nonlinear transmission spectroscopy/technique. These complexes exhibit ¹π-π* transitions/metal-to-ligand charge transfer (¹MLCT) absorption bands in UV-Vis spectral region and green fluorescence assigned to ¹π-π* state mixed with ¹MLCT character. All complexes exhibit obvious AIE in CH₃CN-water solution system. When water fraction increased, nanoparticles of Pt(II) complexes were formed owing to the aggregation, and the emission intensity and triplet excited state lifetime both increased. In addition, complexes Pt-1 – Pt-3 all exhibit triplet transient absorption (TA) in visible region, where reverse saturable absorption (RSA) could occur. The strength of RSA at 532 nm follows the trend: Pt-2 > Pt-3 > Pt-1. The significant AIE, TA and OPL properties of these complexes would be useful for rational design of transition-metal complexes with high emission quantum yield, broadband excited-state absorption, long excited-state lifetime, and strong nonlinear absorption for multi-functional applications.