RESUMO
A bimetallic, two-coordinated carbene-metal-amine (cMa) Au(I) complex featuring a twisted tandem carbene structure (NHC1-Au-NHC2-Au-carbazolyl) was synthesized. The molecular structure in single crystals revealed a large dihedral angle between the two carbene ligands, while the bridged carbene NHC2 and carbazolyl (Cz) ligands were coplanar. A bluish green thermally stimulated delayed phosphorescence (TSDP) was observed in crystals with an emission lifetime over 70 µs, which can be attributed to the spin allowed diabatic population of a high-lying emissive triplet state from the 3LE characterized low-lying ones. The small rotation energy barrier of Cz along the coordination bond allowed conformers with large dihedral angles between NHC2 and Cz. The ICT characterized S1 state was consequently stabilized to achieve a thermally accessible energy gap to facilitate ISC between triplets and the S1, leading to the thermally activated delayed fluorescence (TADF). Simultaneous TSDP and TADF dual emission can be recorded in its doped polymer film owing to the coexistence of these different conformers.
RESUMO
Since the emergence of the first green light emission from a fluorescent thin-film organic light emitting diode (OLED) in the mid-1980s, a global consumer market for OLED displays has flourished over the past few decades. This growth can primarily be attributed to the development of noble metal phosphorescent emitters that facilitated remarkable gains in electrical conversion efficiency, a broadened color gamut, and vibrant image quality for OLED displays. Despite these achievements, the limited abundance of noble metals in the Earth's crust has spurred ongoing efforts to discover cost-effective electroluminescent materials. One particularly promising avenue is the exploration of thermally activated delayed fluorescence (TADF), a mechanism with the potential to fully harness excitons in OLEDs. Recently, investigations have unveiled TADF in a series of two-coordinate coinage metal (Cu, Ag, and Au) complexes. These organometallic TADF materials exhibit distinctive behavior in comparison to their organic counterparts. They offer benefits such as tunable emissive colors, short TADF emission lifetimes, high luminescent quantum yields, and reasonable stability. Impressively, both vacuum-deposited and solution-processed OLEDs incorporating these materials have achieved outstanding performance. This review encompasses various facets on two-coordinate TADF coinage metal complexes, including molecular design, photophysical characterizations, elucidation of structure-property relationships, and OLED applications.
