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.

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.

Hydrogen isotope exchange reactions of phenols and benzyl alcohols have been achieved by a mesoionic carbeneiridium catalyst with high ortho selectivity and high functional group tolerance. Control experiments indicated that acetate is crucial to realize the ortho selectivity, whereas density functional theory calculations supported an outer-sphere direction with hydrogen bonding between acetate and the hydroxyl group.

In recent years, organic mechanofluorochromism (MFC) materials have attracted wide attention in many fields. However, the exploration of MFC materials with highcontrast, high-sensitivity and high-responsiveness remains a challenge. Herein, a series of MFC materials with 2-biarylyl cinchoninic acid skeleton were successfully established, which are based on interconversion of classical/frustrated Brønsted pairs. These compounds have the mechanochromic shift of up to 115 nm, as well as the property of stunning sensitivity and multiple responses to external mechanical force stimuli. The luminescence properties can be easily tuned by changing the substituents.