Synthesis and Photophysical Properties of T‐Shaped Coinage‐Metal Complexes

Abstract

The photophysical properties of as eries of Tshaped coinage d 10 metal complexes,s upportedb yabis-(mesoionic carbene)carbazolide( CNC) pincerl igand,a re explored. The series includes ar are new example of at ri-dentateT -shaped Ag I complex. Post-complexation modification of the Au I complex provides access to al inear cationic Au I complex following ligand alkylation,o rt he first example of ac ationic square planar Au III ÀFc omplex from electrophilic attack on the metal centre. Emissions ranging from blue (Cu I )t oo range (Ag I )a re obtained, with variable contributionso ft hermally-dependentf luorescencea nd phosphorescence to the observed photoluminescence. Green emissions are observed for all three gold complexes (neutralT -shaped Au I ,c ationic linear Au I and square planar cationic Au III ). The higher quantum yield and longer decay lifetimeo ft he linear gold(I) complex are indicative of increased phosphorescence contribution.In the development of efficient organic light emitting devices (OLEDs), basic requirements of phosphorescente mitters include high externalq uantum efficiencies (EQE) of the emission, coupled with appropriater adiative lifetimes in the ordero fm icroseconds to facilitate the intersystem crossing (ISC) from the triplet to the singlet state. [1] These specifications have been amply met using iridium(III) and platinum(II) emitters, [2] with an increasing number of reports detailing the utility of the lesser explored gold(III) complexes. Indeed, CNC- [3] and CCN- [4] cyclometallated gold(III) complexes excelling in emissioncolor tuning, solubility and thermals tability have recently yielded OLEDsw ith very high EQEs and similarly long device operationalh alf-lifetimes. [4b] Lowero xidation state gold(I), and the other d 10 coinage metals, copper(I) and silver(I), have also been the focus of concurrent investigationsi nto their use in OLEDs. One of the more successful design strategieso nt his front employs the linear bonding geometry of carbene-metal-amides (CMAs),i nw hich all three d 10 metals (Cu I ,A g I and Au I ), have similarly accomplished excellent EQE performance and/or high brightnessO LED operation, notably employing carbazolide derivativesa st he donor amidep artnersw ith the acceptor carbenes. [5] These CMAsc an display particularly short (ns) emission lifetimesi nt hermally assisted delayed fluorescence (TADF), basedo nt he rapid triplet-to-singlet ISC, unlike the heavya tom (metal) phosphorescente mitters relying on spinorbit coupling. [1b, 6] The dependency of photoluminescence on the coordination geometry of d 10 coinage metal complexes is well-known, [7] for example, 3-coordinate trigonal planar copper(I)c omplexes showed tunable behavior from pure phosphorescence to TADF dependingo nt he carbene-metal-amine dihedral angles. [7c] Extending 3-coordinate systemsb eyondt rigonal planar geometries to ag round state Jahn Teller-distorted T-shape has been an early theoretical target for photophysical tuning of the singlet-triplet gap. [8] However,t he availab...

A Cytotoxic Bis(1,2,3‐triazol‐5‐ylidene)carbazolide Gold(III) Complex Targets DNA by Partial Intercalation

“…The geometry of the Au III ion is square planar with all the associated bond angles approaching 90° (avg C carbene −Au−N, 88.94(12)°; C carbene −Au−Cl, 91.54(10)°) and both bond angles of N−Au−Cl (172.97(9)°) and C carbene −Au−C carbene (171.54(14)°) deviate slightly from linearity. The average Au−C carbene bond length increased slightly to 2.047(4) Å compared with the Au I precursor, 4 a (2.023(3) Å), while the Au−N amido bond length significantly decreased to 2.010(3) Å from 2.445(3) Å, consistent with the higher oxidation state for the metal [64,65] . The C carbene −Au−C carbene plane is slightly twisted in relation to the carbazole moiety with a twist angle of 15.30(3)°, whereby one of the triazoles rings (C1) is orientated 4.6° above the carbazole moiety mean plane, while the other triazole ring is canted by 21.3(6)° below the plane.…”

“…[74] Generally, oxidations of Au I ‐NHC to Au III ‐NHC complexes are accompanied by an upfield carbene 13 C resonance shift of 20–30 ppm [75] . However, in the case of 3 b and 4 b , the carbene resonances were not observed, in accord with the fluorinated analogue of 3 b [65] . Crystals of 4 b were obtained from a saturated CH 2 Cl 2 solution layered with toluene at room temperature and the solid‐state structure is shown in Figure 1b.…”

“…We previously reported that a monoanionic CNC pincer ligand with a carbazole backbone and two flanking trz groups successfully stabilized reactive first row late transition metals [63] . Notably, the gold derivative could be oxidized to robust Au III complexes [64,65] . The enhanced redox stability and the planar aromatic carbazole moiety present ideal attributes to be explored further for DNA binding and cytotoxicity towards cancer cells.…”

Bright luminescent lithium and magnesium carbene complexes

“…[41][42][43][44] Similar ligands, which had been studied mainly as NNN pincers (Fig. 1 II), [45][46][47][48][49][50][51][52][53][54][55][56][57] have been pioneered by Bezuidenhout [58][59][60][61][62] (CNC pincer, C: mesoionic carbene MIC; III and IV) and Kunz [63][64][65][66][67][68] (CNC pincer, C: N-heterocyclic carbene NHC; V). Mesoionic carbenes, [69][70][71][72][73][74][75] in general, and 1,2,3-triazolinylidenes, in particular, excel through their donating properties 76,77 and, as such, are expected to stabilize high-valent transition metals.…”

“…1 , IV ). 62 They found that the luminescence wavelength is tunable by the judicious choice of the metal. Thereby, the copper( i ) complex emitted in the blue- (quantum yield Φ em = 0.8%), the silver( i ) in the orange- ( Φ em = 2.4%), and the gold( i ) complex in the green- ( Φ em = 0.6%) regions of the spectrum.…”