N-Alkyl Chain Induced Molecular Aggregation in Mononuclear Gold(I)-N-Heterocyclic Carbene Complexes for Blue Light Emitting Applications

We report the photoluminescence and thermal stability correlation between blue emitting mononuclear gold(I)-NHC chloride complexes, N-(9-anthracenyl)-N'(n-alkyl)imidazol-2-ylidene gold(I) chloride (alkyl = n-butyl (1), n-pentyl (2), n-hexyl (3)). The solid-state study reveals a unique molecular packing due to hydrogen bonding, aurophillic interaction, and CH···π interactions in all 1-3. In addition, the π···π stacking has been found in 1. All these complexes show good thermal stability due to the strong metal-ligand bond strength along with crystal packing. In addition, 1-3 emits a blue colour in both solution and crystalline state. The quantum yield in the crystalline state was found to be high for 1 (22.44%) compared to 2 (9.90%), and 3 (14.98%). A similar high quantum yield for blue-emitting gold(I)-NHC chloride complex is rare. This promising quantum yield for 1 can be ascribed to the crystal packing effect. The theoretical calculations were carried out to understand the electronic and structural properties of 1-3. Computational studies revealed the origin of the luminescence behaviour of complexes. The blue light emitting thin film and LED are demonstrated using 1 exhibited the emission peak at the blue region with Commission Internationale de L'Eclairage (CIE) coordinates near the National Television Standards Committee (NTSC) value.