Phosphorescent carbene-gold-arylacetylide materials as emitters for near UV-OLEDs

A series of carbene-gold-acetylide complexes [(BiCAAC)AuCC]nC6H5-n (n = 1, Au1; n=2, Au2; n=3, Au3; BiCAAC = bicyclic(alkyl)(amino)carbene) have been synthesized in high yields. All complexes show excellent thermal stability up to 342℃. Compounds Au1–Au3 exhibit deep-blue to blue-green phosphorescence with good quantum yields up to 43% in all media. An increase of the (BiCAAC)Au moieties in gold complexes Au1–Au3 increases the extinction coefficients in the UV-vis spectra and stronger oscillator strength coefficients supported by theoretical calculations. The luminescence radiative rates decrease with an increase of the (BiCAAC)Au moieties. The time-dependent density functional theory (TD-DFT) study supports a charge-transfer nature of the phosphorescence due to the large (0.5–0.6 eV) energy gap between singlet excited (S1) and triplet excited (T1) states. Transient luminescence study reveals the presence of both non-structured UV prompt-fluorescence and vibronically resolved long-lived phosphorescence 428 nm. Organic light-emitting diodes (OLED) have been fabricated by physical vapour deposition with 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) as a host material with complex Au1. The near-UV electroluminescence is observed at 405 nm with device efficiency of 1% while demonstrating OLED device lifetime LT50 up to 20 min at practical brightness of 10 nits, indicating a highly promising class of materials to develop stable UV-OLEDs.