Alkynyl-Gold Carbazole Hybrids: Luminescence and Functionalization via iClick Reactions

A series of structurally diverse gold(I) complexes bearing the 9-(4-ethynylphenyl)-9H-carbazole chromophore were synthesized, featuring mononuclear, dinuclear, tricoordinated, and supramolecular architectures. Their formation involved either alkynylation reactions or the reaction of polymeric alkynyl species [Au(C≡CR)]_n with auxiliary ligands. Notably, an equilibrium between bimetallic and tricoordinated species was observed when diphosphine ligands were employed, highlighting the dynamic nature of these systems. This equilibrium was found to be solvent-dependent, with the pure tricoordinated complex isolable in a nonpolar solvent. The triazole complexes were synthesized via iClick chemistry by reacting the carbazole-functionalized alkyne with azide-phosphine gold(I) precursors. Structural analysis confirmed hydrogen-bonding frameworks and the absence of π-π stacking. Photophysical studies demonstrated intense solid-state phosphorescence, with blue-green luminescence markedly enhanced at 77 K. At room temperature, emission broadened (450-600 nm) and red-shifted compared to the free ligand, indicating a synergistic contribution of carbazole-centered (³IL) and intramolecular charge transfer (ICT) transitions. This metal-tuned photophysical behavior underscores the potential of these gold complexes in luminescent materials. This charge transfer, occurring from the carbazole to the ligand system is mediated by the phenyl ring and modulated by metal coordination. TD-DFT calculations were performed to analyze the molecular orbitals involved in both the absorption (S0 → S₁) and emission (T₁ → S0) transitions of the complex 1, indicating that the emission is predominantly of intraligand character, although coordination to the Au(I) center induces slight modifications in the energy levels and transition intensities.