Linear Carbene Pyridine Copper Complexes with Sterically Demanding N,N′-Bis(trityl)imidazolylidene: Syntheses, Molecular Structures, and Photophysical Properties

Abstract

The sterically demanding carbene ITr (N,N′bis(triphenylmethyl)imidazolylidene) was used as a ligand for the preparation of luminescent copper(I) complexes of the type [(ITr)Cu(R-pyridine/R′-quinoline)]BF 4 (R = H, 4-CN, 4-CHO, 2,6-NH 2 , and R′ = 8-Cl, 6-Me). The selective formation of linear, bis(coordinated) complexes was observed for a series of pyridine and quinoline derivatives. Only in the case of 4-cyanopyridine a one-dimensional coordination polymer was formed, in which the cyano group of the cyanopyridine ligand additionally binds to another Cu atom in a bridging manner, thus leading to a trigonal planar coordination environment. In contrast, employing sterically less demanding monotrityl-substituted carbene 3, no (NHC)Cu-pyridine complexes could be prepared. Instead, a bis-carbene complex [(3) 2 Cu]PF 6 was obtained which showed no luminescence. All linear pyridine/quinoline coordinated complexes show weak emission in solution but intense blue to orange luminescence doped with 10% in PMMA films and in the solid state either from triplet excited states with unusually long lifetimes of up to 4.8 ms or via TADF with high radiative rate constants of up to 1.7 × 10 5 s −1 at room temperature. Combined density functional theory and multireference configuration interaction calculations have been performed to rationalize the involved photophysics of these complexes. They reveal a high density of low-lying electronic states with mixed MLCT, LLCT, and LC character where the electronic structures of the absorbing and emitting state are not necessarily identical.

So Close, Yet so Different: How One Donor Atom Changes Significantly the Photophysical Properties of Mononuclear Cu(I) Complexes

“…For compound 1P, this dependency is a convex up decreasing function, similar to the one already observed for Cu(I) carbene complexes. 54 As shown in Figure 5, the excited-state lifetimes smoothly decrease with an increase in temperature. We anticipate that this is a result of an increase of k nr that includes a flattening of the Cu(I) complexes at higher temperatures.…”

“…The temperature evolution of the excited-state lifetimes for complexes 1P and 3P also has an unexpected character (Figure , Tables S5 and S6). For compound 1P , this dependency is a convex up decreasing function, similar to the one already observed for Cu­(I) carbene complexes . As shown in Figure , the excited-state lifetimes smoothly decrease with an increase in temperature.…”

Trigonal Copper(I) Complexes with Cyclic (Alkyl)(amino)carbene Ligands for Single-Photon Near-IR Triplet Emission

“…10 s –1 . Similarly, long-lived states have been observed in linear copper­(I) NHC pyridine complexes …”

“…Similarly, long-lived states have been observed in linear copper(I) NHC pyridine complexes. 77 According to our calculations, the T 1 state of trigonal 2−4 undergoes significant distortion upon geometry relaxation toward a T-shape including torsion of the ligand planes, which are then nearly coplanar (Table 3 and Figure 4, Supporting Information).…”

Thermally Activated Delayed Fluorescence Mechanism of a Bicyclic “Carbene–Metal–Amide” Copper Compound: DFT/MRCI Studies and Roles of Excited-State Structure Relaxation

“…The PCM − solvation model was adopted to account for the solvent effects of toluene. Subsequently, single-point energies of all of the DFT- and TD-DFT-optimized structures were refined with the DFT/MRCI method, in which the BH-LYP functional and the R2018 Hamiltonian were employed, which have been demonstrated to work very well for organometallic compounds. − The def2-SVP basis sets were used for the C, H, N, and Cu atoms, while the SDD pseudopotential was used for the Cu atom. Orbital composition analysis was performed with the Multiwfn3.7 package .…”