Direct Observation of the Triplet Excited States and Dynamics of Platinum(II)-Tetraphenylethylene Complexes by Time-Resolved Transient Absorption Spectroscopy

Abstract

Tetraphenylethylene (TPE) is one of the most widely utilized luminogens in aggregation-induced emission research areas and is employed to cooperate with Pt(II) complexes to build supramolecular self-assemblies and light-emitting materials. However, little appears to be known about the underlying excited states dynamics of such Pt(II)-TPE materials to date. In this work, we synthesized TPE containing Pt(II) acetylide complexes to study the photophysical properties of these complexes by employing resonance Raman and time-resolved transient absorption spectroscopies. The photophysical dynamical evolutions of TPE containing Pt(II) acetylide complexes and the effects of TPE on the lifetimes of triplet excited states are discussed. The time-resolved transient absorption spectroscopic measurements reveal that two different triplet metal-to-ligand charger transfer [3MLCT dπ(Pt) → π*(tpy/bpy) and 3MLCT dπ(Pt) → π*(TPE)] excited states are observed directly. Significantly, the 3MLCT [dπ(Pt) → π*(TPE)] excited state lifetimes are considerably short due to the intramolecular rotation of TPE that speeds up the nonradiative decay of the corresponding triplet excited states.