Photofunctional Platinum Complexes Featuring N‐heterocyclic Carbene‐Based Pincer Ligands

Abstract

Photoactive platinum complexes of stoichiometry [Pt((R)CCC(R))L](0/+) (R = Me, nBu and L = -CN, -C≡CPh, -N≡CCH3, -Py, -CO) featuring pincer-type bis N-heterocyclic carbene (NHC) ligands ((R)CCC(R)) were synthesized. Organometallic syntheses of these complexes are facile and achievable through standard laboratory procedures. Control of intermolecular Pt⋅⋅⋅Pt interaction, π-π stacking, and emission tuning is achieved through suitable choice of the NHC-wingtip substituent (R) and the auxiliary ligand (L). Exposure to specific volatile organic compounds (VOCs) or mechanical grinding triggers changes in emission colors, which render these complexes photofunctional. Solid-state structures and photoluminescence results are described herein.

Pure blue phosphorescent platinum(ii) emitters supported by NHC-based pincer type ligands with unitary emission quantum yields

“…In accordance with previous works, 26,28,29,55 the [Pt(C NHC ^C Ar ^C NHC )L] emitters described in this work show emissive excited states with strong 3 IL (π, π*) character that are mainly localized on the C NHC ^C Ar ^C NHC ligand, as evidenced by a number of experimental observations; these include (i) structured emission spectra with distinct vibronic progressions of 1300–1500 cm −1 , (ii) slight perturbation of emission energy upon change of the ancillary ligand (Δ λ em <8 nm; <460 cm −1 ), (iii) a minor solvatochromic effect and rigidochromic effect (Δ λ em <3 nm; <150 cm −1 ) and (iv) TA spectral profiles largely independent of the ancillary ligand. This predominant 3 IL character of the emissive excited state allows tuning of the emission energy through modifying substituents of the C NHC ^C Ar ^C NHC ligand scaffold.…”

“…Similar to previous findings, 26,28,29 the [Pt(C NHC ^C Ar ^C NHC )L] complexes in this work are prone to excimer formation in solution and thin films at elevated concentrations, giving rise to a broad low-energy excimer emission band at approximately 540–600 nm. As noted from the emission spectra recorded in PMMA and CH 2 Cl 2 solutions, apart from the influence of the C NHC ^C Ar ^C NHC ligand scaffold, the extent of excimer emission showed a strong dependence on the ancillary ligand and generally followed a descending order of CN > CNBPh 3 > Cl > CNB(C 6 F 5 ) 3 ≈ pyrazolate.…”

“…The C NHC ^C Ar ^C NHC pincer ligands were synthesized according to the literature. 25,28,29 Complexes 1–4 were prepared by reacting Pt(COD)Cl 2 with the [Zr( iv )(C NHC ^C Ar ^C NHC )] species in situ generated from the reaction of the pincer ligand and Zr(NMe 3 ) 4 . Among these complexes, 1 was previously reported.…”

“…Complexes 1 – 4 display intense absorption bands ca. 250–270 nm ( ε ∼ 1.0–2.5 × 10 4 M −1 cm −1 ), attributed to 1 IL π–π* transitions of the C NHC ^C Ar ^C NHC ligand, 26,28,29 and moderately intense absorption bands at ca. 280–380 nm ( ε ∼ 3.6–6.8 × 10 3 M −1 cm −1 ), which are tentatively assigned as an admixture of 1 IL/ 1 MLCT [dπ(Pt) → π*(C NHC ^C Ar ^C NHC )] transitions.…”

Room‐Temperature Phosphorescent Platinum(II) Alkynyls with Microsecond Lifetimes Bearing a Strong‐Field Pincer Ligand

“…In recent investigations, numerous groups have reported bis(N-heterocyclic carbene)pyridyl/phenyl complexes of platinum(II) that emit mixed 3 MLCT/ 3 LLCT phosphorescence (LLCT = interligand charge transfer) that is tunable by varying the alkynyl ligand. [16][17][18][19][20][21][22][23][24][25] Many platinum(II) metallacycles aggregate in the ground state, and often in the excited state to form excimers. [17,26,27] Ground-state aggregation can confer such properties as vapochromism, photochromism, and mechanochromism in solids, leading to applications as sensors and switches.…”