Synthesis, Characterization and Photophysical Properties of Mesoionic N-Heterocyclic Imines.

N-heterocyclic imines are widely used in transition-metal chemistry, main-group chemistry as well as catalysis, due to their enhanced basicity and nucleophilicity which benefit from their ylidic form. As their analogs, mesoionic N-heterocyclic imines, which feature more highly ylidic form, is still in its infancy though excellent works also achieved. Here we reported the synthesis, characterization and photophysical properties of mesoionic N-heterocyclic imines. TD-DFT are employed to get deeper insight into the mechanism of the photophysical behaviors. The unsubstituted mesoionic N-heterocyclic imines (4-6) displayed considerable quantum yields (QY: up to 43.8%) and could be potentially applied as luminescent materials.

Experimental and Computational Study on Photophysical Properties of Mesoionic Chalcogenones.

N-Heterocyclic carbene adducts with main group elements (NHC=E) have aroused great interest and have been widely investigated in coordination chemistry. Among them, N-heterocyclic carbene adducts with chalcogens (NHC=Ch) have been known for a long time. Their investigations mostly focused on synthesis, coordination chemistry and electrochemistry. Their photophysical properties still remain unexplored. In this work, the photophysical properties of mesoionic carbene adducts with sulfur and selenium have been investigated both in solution and solid state. These compounds showed blue fluorescence in dichloromethane. While in solid state, orange to red room-temperature phosphorescence can be observed, and dual emission was found in mesoionic thiones. Furthermore, time-dependent density functional theory (TD-DFT) calculations were used to obtain insights into the luminescent mechanism.

Nucleophilic Activation of Sulfur Hexafluoride by N-Heterocyclic Carbenes and N-Heterocyclic Olefins: A Computational Study.

Sulfur hexafluoride (SF6 ) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF6 is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF6 has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF6 in high efficiency.