A Carbazole-Bridged Biscyclometalated Diplatinum Complex: Synthesis, Characterization, and Dual-Mode Aggregation-Enhanced Phosphorescence

A cationic carbazole-bridged biscyclometalated diplatinum complex 4 has been synthesized and characterized. Single-crystal X-ray analysis demonstrates that complex 4 displays a dimeric structure with noncovalent pi-pi stacking and unique double Pt-Pt interactions. In aerated dilute CH3CN, complex 4 is characterized by a very weak monomeric yellow emission (lambda(emi) = 547 nm; Phi = 0.51%), which is attributed to the triplet intraligand ((LC)-L-3) excited state mixing with some charge transfer characters. In contrast, under aerated conditions, the dispersion of 4 in a mixed solvent of CH3CN/Et2O (1/9, v/v) or CH3CN/H2O (1/9, v/v) displays intense yellow (lambda(emi) = 550 nm; Phi = 35.5%; tau = 11.10 mu s) and red emission (lambda(emi) = 635 nm; Phi = 14.1%; tau = 7.00 mu s), respectively. These aggregation-induced phosphorescent emission enhancements are considered being caused by the oxygen-shielding effect and the molecular rigidification-induced decrease of nonradiative decays in the aggregate state. The morphology and size of the aggregates under these two conditions are examined by scanning electron microscope and dynamic light scattering analysis. The absorption and emission properties of 4 are further rationalized by time-dependent density functional theory calculations on a model compound.

Automated summary

A cationic carbazole-bridged biscyclometalated diplatinum complex 4 has been synthesized and characterized, showing different fluorescence properties under different solvent conditions and enhanced phosphorescent emission in aggregate state. Analysis through X-ray and density functional theory calculations revealed that the phosphorescent emission enhancement is mainly caused by the oxygen-shielding effect and molecular rigidification-induced decrease of nonradiative decays in the aggregate state.