Color modulation in organometallic dyes. Purple-colored acyclic carbenes derived from 2-isocyanoazulene gold(I) complexes

Abstract

This study reports new carbene azulene gold(I) complexes [AuCl{C(NHAz)(NR2)}] (R = Me (1) and nBu (2)) and [Au(C6F4OC10H21){C(NHAz)(NR2)}] (R = Me (3) and nBu (4)) prepared by reaction of 2-isocyanoazulene gold(I) complexes [AuX(CNAz)] (X = Cl and C6F4OC10H21) with the corresponding secondary amines. Their photophysical properties were investigated by absorption and emission spectroscopies, and by TD-DFT calculations. All the compounds display an intense coloration based on HOMO-LUMO transitions, dominated by the azulene core. Gold-isocyanide complexes show a slight bathochromic shift related to azulene, while a hypsochromic shift was observed after formation of carbene complexes. Thus, the transformation of the gold-isocyanide group into the gold-carbene functionality produces a substantial color change from blue to deep purple. This different electronic behavior is mainly due to the stabilization of the LUMO orbital in the isocyanide complexes, and to the stabilization of the HOMO in the carbene derivatives. These carbene gold complexes show fluorescence in solution associated with the azulene core. This work illustrates how the synthetically easy isocyanide-carbene transformation open new perspectives to a fine color modulation in organometallic azulene dyes.