Platinum(II)-Substituted Phenylacetylide Complexes Supported by Acyclic Diaminocarbene Ligands

Abstract

We introduce phosphorescent platinum aryl acetylide complexes supported by tert-butyl-isocyanide and strongly σ-donating acyclic diaminocarbene (ADC) ligands. The precursor complexes cis-[Pt­(CNtBu)2(CCAr)2] (4a–4f) are treated with diethylamine, which undergoes nucleophilic addition with one of the isocyanides to form the cis-[Pt­(CNtBu)­(ADC)­(CCAr)2] complexes (5a–5f). The new compounds incorporate either electron-donating groups (4-OMe and 4-NMe2) or electron-withdrawing groups [3,5-(OMe)2, 3,5-(CF3)2, 4-CN, and 4-NO2] on the aryl acetylide. Experimental HOMO–LUMO gaps, estimated from cyclic voltammetry, span the range of 2.68–3.61 eV and are in most cases smaller than the unsubstituted parent complex, as corroborated by DFT. In the ADC complexes, peak photoluminescence wavelengths span the range of 428 nm (2a, unsubstituted phenylacetylide) to 525 nm (5f, 4-NO2-substituted), with the substituents inducing a red shift in all cases. The phosphorescence E 0,0 values and electrochemical HOMO–LUMO gaps are loosely correlated, showing that both can be reduced by either electron-donating or electron-withdrawing substituents on the aryl acetylides. The photoluminescence quantum yields in the ADC complexes are between 0.044 and 0.31 and the lifetimes are between 4.8 and 14 μs, a factor of 1.8–10× higher (for ΦPL) and 1.2–3.6× longer (for τ) than the respective isocyanide precursor (ΦPL = 0.014–0.12, τ = 2.8–8.2 μs).

Efficient blue-phosphorescent trans-bis(acyclic diaminocarbene) platinum(ii) acetylide complexes

“…The aryl acetylide substitution pattern has the largest effect on the emission maximum, with both electron-donating ( 4b ) and electron-withdrawing ( 4c ) substituents inducing a red shift relative to the unsubstituted complex 4a , consistent with our previous study on mono-ADC platinum acetylide compounds. 21 These observations suggest that the emissive states mainly localize on the acetylide ligands. Replacing the nucleophile used to prepare the ADC has minimal effect on the emission profile but has a subtle effect on quantum yield with 4d (dimethylamine, Φ PL = 0.30) < 4e (pyrrolidine, Φ PL = 0.35) < 4a (diethylamine, Φ PL = 0.43); this trend may stem from the slightly increasing steric profile in this series, which can reduce intermolecular interactions known to cause emission self-quenching in Pt complexes.…”

“…in energy. The oxidation potentials are shied to lower potential compared to mono-ADC analogues, 20,21 suggesting an increase in electron density on the platinum complex when the second ADC is added. In the bis-ADC complexes reported here, the rst oxidation potentials, reported as anodic potentials (E p,a ) since they are all irreversible, range from 0.35-0.87 V vs. the ferrocene couple (Fc + /Fc) in 4a-4e; the corresponding wave is poorly resolved in 4f.…”

“…1). 20,21 The ADC is among the strongest known s-donor ligand classes, surpassing the N-heterocyclic carbene (NHC) family that is commonly used in blue-phosphorescent compounds. 5,12,13,22,23 Installation of the ADC by nucleophilic addition resulted in signicant improvement in photophysical properties compared to the bis-isocyanide precursor (1 in Fig.…”

Substituent-Dependent Azide Addition to Isocyanides Generates Strongly Luminescent Iridium Complexes

“…An emerging strategy in the design of cyclometalated iridium complexes and other classes of organometallic phosphors is to use ligand-based functionalization strategies to install supporting ligands not able to be accessed by traditional means. The best-developed example of this approach involves addition of a nitrogen-based nucleophile to a coordinated isocyanide, which forms an acyclic diaminocarbene (ADC). , Our group has used this method to install ADCs onto luminescent iridium , or platinum , complexes and showed the strong σ-donor ADCs are particularly effective at supporting efficient deep-blue phosphorescence, , and related approaches have been used to good effect by a few other groups in the design of iridium, , rhenium, or platinum , phosphors supported by ADCs.…”

“…The best-developed example of this approach involves addition of a nitrogen-based nucleophile to a coordinated isocyanide, which forms an acyclic diaminocarbene (ADC). 25,26 Our group has used this method to install ADCs onto luminescent iridium 27,28 or platinum 29,30 complexes and showed the strong σ-donor ADCs are particularly effective at supporting efficient deep-blue phosphorescence, 29,31 and related approaches have been used to good effect by a few other groups in the design of iridium, 7,32 rhenium, 33 or platinum 34,35 phosphors supported by ADCs.…”