Au(I) Complex With an Abnormal Carbene Ligand Shows Anti-Kasha Dual Photoluminescence Emission.

We report the first photoactive linear Au(I) complex with an abnormal N-heterocyclic carbene (aNHC) ligand, Au(aIm)(Cz). The complex exhibits an anti-Kasha dual fluorescence behavior comprised of the high-energy, short-lived fluorescence and low-energy, long-lived thermally activated delayed fluorescence (TADF). The anti-Kasha emission emerges through rapid intersystem crossing (ISC) to the triplet manifold, followed by thermally activated reverse ISC to the singlet ligand-to-ligand charge-transfer transition state. The aNHC ligand significantly weakens the mediation of Au in electronic transitions, thereby enabling dual fluorescence emissions. Beyond its intriguing photophysics, Au(aIm)(Cz) shows practical utility as a dual-modal fluorescence sensor for phenyl sulfate, an important marker for diabetic kidney damage. The system exhibits a large dynamic range in both the fluorescence intensity ratio and lifetime, enabling robust detection of phenyl sulfate with high selectivity over biologically relevant interferents. These findings establish abnormal carbene coordination as a powerful design strategy for engineering unconventional excited-state processes in photoactive linear Au(I) complexes.