Acridine <i>N</i>‐Heterocyclic Carbene Gold(I) Compounds: Tuning from Yellow to Blue Luminescence

Abstract

Abstract The synthesis and the luminescence features of three gold(I)‐ N ‐heterocyclic carbene (NHC) complexes are presented to study how the n ‐alkyl group can influence the luminescence properties in the crystalline state. The mononuclear gold(I)‐NHC complexes, [( L 1 )Au(Cl)] ( 1 ), [( L 2 )Au(Cl)] ( 2 ), and [( L 3 )Au(Cl)] ( 3 ) were isolated from the reactions between [(tht)AuCl] and corresponding NHC ligand precursors, [ N ‐(9‐acridinyl)‐ N’ ‐( n ‐butyl)‐imidazolium chloride, ( L 1 .HCl)], [ N ‐(9‐acridinyl)‐ N’ ‐( n ‐pentyl)‐imidazolium chloride, ( L 2 .HCl)] and [ N ‐(9‐acridinyl)‐ N’ ‐( n ‐hexyl)‐imidazolium chloride, ( L 3 .HCl)]. Their single‐crystal X‐ray analysis reveals the influence of the n ‐alkyl groups on solid‐state packing. A comparison of the luminescence features of 1 – 3 with n ‐alkyl substituents is explored. The molecules 1 – 3 depicted blue emission in the solution state, while the yellow emission (for 1 ), greenish‐yellow emission (for 2 ), and blue emission (for 3 ) in the crystalline phase. This paradigm emission shift arises from n ‐butyl to n ‐pentyl and n ‐hexyl in the crystalline state due to the carbon‐carbon rotation of the n‐ alkyl group, which tends to promote unusual solid packing. Hence n ‐alkyl group adds a novel emission property in the crystalline state. Density Functional Theory and Time‐Dependent Density Functional Theory calculations were carried out for monomeric complex, N ‐(9‐acridinyl)‐ N’ ‐( n ‐heptyl)imidazole‐2‐ylidene gold(I) chloride and dimeric complex, N ‐(9‐acridinyl)‐ N’ ‐( n ‐heptyl)imidazole‐2‐ylidene gold(I) chloride to understand the structural and electronic properties.