Cyclic (Amino)(aryl)carbenes Enter the Field of Chromophore Ligands: Expanded π System Leads to Unusually Deep Red Emitting Cu^I Compounds

Abstract

A series of copper­(I) complexes bearing a cyclic (amino)­(aryl)­carbene (CAArC) ligand with various complex geometries have been investigated in great detail with regard to their structural, electronic, and photophysical properties. Comparison of [CuX­(CAArC)] (X = Br (1), Cbz (2), acac (3), Ph2acac (4), Cp (5), and Cp* (6)) with known CuI complexes bearing cyclic (amino)­(alkyl), monoamido, or diamido carbenes (CAAC, MAC, or DAC, respectively) as chromophore ligands reveals that the expanded π-system of the CAArC leads to relatively low energy absorption maxima between 350 and 550 nm in THF with high absorption coefficients of 5–15 × 103 M–1 cm–1 for 1–6. Furthermore, 1–5 show intense deep red to near-IR emission involving their triplet excited states in the solid state and in PMMA films with λem max = 621–784 nm. Linear [Cu­(Cbz)­(DippCAArC)] (2) has been found to be an exceptional deep red (λmax = 621 nm, ϕ = 0.32, τav = 366 ns) thermally activated delayed fluorescence (TADF) emitter with a radiative rate constant k r of ca. 9 × 105 s–1, exceeding those of commercially employed IrIII- or PtII-based emitters. Time-resolved transient absorption and fluorescence upconversion experiments complemented by quantum chemical calculations employing Kohn–Sham density functional theory and multireference configuration interaction methods as well as temperature-dependent steady-state and time-resolved luminescence studies provide a detailed picture of the excited-state dynamics of 2. To demonstrate the potential applicability of this new class of low-energy emitters in future photonic applications, such as nonclassical light sources for quantum communication or quantum cryptography, we have successfully conducted single-molecule photon-correlation experiments of 2, showing distinct antibunching as required for single-photon emitters.

Two-photon excited deep-red and near-infrared emissive organic co-crystals

“…CNC-T exhibits (Fig. 4b ) deep-red fluorescence 51 with a peak at 638 nm, while CNC-Q displays (Fig. 4b ) deep-red and NIR fluorescence with a maximum emission wavelength at 668 nm, which is red-shifted by 162 nm compared to that of the COR crystals.…”

A Luminescent Two‐Coordinate AuIBimetallic Complex with a Tandem‐Carbene Structure: A Molecular Design for the Enhancement of TADF Radiative Decay Rate

“…Experimental [3a–h, j–o, 6] and theoretical [14] investigations of the photophysics of (C:)M I X compounds have been limited largely to the monometallic complexes. Multinuclear complexes with two‐coordinate metal centres similar to (C:)M I X have been shown to emit from aurophilic and metallophilic interactions; [3b, 15] however, reports of luminescence from multinuclear (C:)M I X compounds without metal‐metal transitions are scarce [16] .…”

Bright luminescent lithium and magnesium carbene complexes

“…Recent remarkable achievements comprise the emissive properties of two-coordinate coinage metal complexes. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] There, embedding copper(I) in a push-pull electronic environment provided by a π-acidic carbene 33 and a π-donating carbazolido ligand (Fig. 1 I), resulted in a 100% quantum yield of the 474 nm luminescence and an excited state lifetime of 2.8 μs.…”