Synthesis, characterization, luminescence and non-linear optical properties of diimine platinum(II) complexes with arylacetylene ligands

Alkynylphosphonium Pt(II) Complexes: Synthesis, Characterization, and Features of Photophysical Properties in Solution and in the Solid State

A series of heteroleptic bis-alkynyl-diimine mononuclear Pt(II) complexes with alkynylphosphonium and di-tert-butyl-2,2'-bipyridine (dtbpy) ligands have been prepared and characterized by spectroscopic methods and single-crystal XRD. The Pt(II) complexes obtained in the present study demonstrate triplet emission in solution, which originates from 3MLCT/3LC states where the nature of the π-conjugated linker in the alkynylphosphonium ligand manages the contributions of each transition, and this conclusion is supported by DFT calculations. Additionally, the presence of the phosphonium group connected to alkynyl through the π-conjugated linker enhances nonlinear optical properties of the Pt(II) complexes increasing two-photon absorption cross section up to 400 GM. In the solid state, the Pt(II) complexes demonstrate emission that is attributed to 3MMLCT transitions due to the presence of Pt-Pt metallophilic interactions, and the reversible assembly and disassembly of these interactions by grinding and solvent treatment are responsible for the mechanochromic luminescence. It has been experimentally shown that stimuli-responsive emission of the Pt(II) complexes is the result of a "monomer/dimer" transformation; this conclusion is confirmed by DFT calculations for discrete complexes and different dimers with or without Pt-Pt interactions.

First hyperpolarizabilities of Pt(4-ethynylbenzo-15-crown-5)2(bpy) derivatives with the complexation of mono-cations (Li+, Na+, K+) and di-cations (Mg2+, Ca2+): development of a cation detector

The coordination of mono-cations and di-cations onto the crown merits the design of the NLO-based cation detector.

Triangular platinum(II) metallacycles: syntheses, photophysics, and nonlinear optics

Three triangular platinum(II) diimine metallacycles incorporating large cyclic oligo(phenylene-ethynylene) (OPE) bisacetylide ligands are synthesized, and their photophysical properties are studied. Two types of triplet excited states with ligand/metal-to-ligand charge-transfer and acetylide-ligand-centered characteristics respectively, are exhibited by these complexes depending on the size (conjugation length) and electronic features of the cyclic OPE ligands. When the energy levels of the two excited states are close to each other, the lowest triplet state is found to switch between the two in varied solvents, resulting from their relative energy inversion induced by solvent polarity change. Density functional theory and time-dependent density functional theory calculations provide corroborative evidence for such experimental conclusions. More importantly, the designed metallacycles show impressive two-photon absorption (2PA) and two-photon excitation phosphorescing abilities, and the 2PA cross section reaches 1020 GM at 680 nm and 670 GM at 1040 nm by two different metallacycles. Additionally, pronounced reverse saturable absorptions are observed with these metallacycles by virtue of their strong transient triplet-state absorptions.