Tetragold(I) Complexes: Solution Isomerization and Tunable Solid-State Luminescence

In this study, a new family of tetranuclear
gold­(I) triphosphine
derivatives bearing alkynyl and thiolate groups have been efficiently
synthesized by treating the polymeric acetylides (AuC2R)n or a thiolate (AuSPh)n sequentially with the (a) phosphine ligand and (b) cationic
complex [Au3(P^P^P)2]3+ (P^P^P =
PPh2CH2PPhCH2PPh2). The
clusters [Au4(P^P^P)2(C2R)2]2+ [R = Ph (1), biphenyl (2), terphenyl (3), C6H4OMe (4), C6H4NMe2 (5), C6H11O (6), and C6H4CF3 (7)] and [Au4(P^P^P)2(SPh)2]2+ (8) were characterized by X-ray crystallography in the solid state.
NMR spectroscopic investigations in solution revealed that the majority
of alkynyl clusters 1–7 exist as
two isomeric species in slow chemical equilibria. All complexes 1–8 exhibit moderate-to-strong photoemission
in the solid state with quantum yields from 0.07 to 0.51. The luminescence
behavior was rationalized using quantum chemical density functional
theory methods. The high emission efficiency of these tetragold­(I)
compounds and their good stability in film allowed for the fabrication
of an organic electroluminescent device (OLED). Employing complex 5 (Φ = 0.51), an OLED was fabricated under a solution
process to give a good external quantum efficiency of 3.1%, corresponding
to a current efficiency of 6.1 cd/A and a power efficiency of 5.3
lm/W, with Commission Internationale de I’Eclairage coordinates
of (0.52, 0.46).