ABSTRACT Low energy triplet emitters are highly relevant for the development of OLEDs and fiber optics‐based IT applications, but typically suffer from nonradiative decay due to the energy gap law (EGL). Excited state deactivation can be limited by enhancing the radiative decay rate via thermally activated delayed fluorescence (TADF), bypassing spin‐forbidden phosphorescence. We report on linear copper(I) complexes bearing a recently reported [2.2]isoindolinophanyl‐carbene (iPC) ligand as potent excited state π‐acceptor. The compounds show efficient TADF from ligand‐to‐ligand charge transfer ( 1/3 LLCT) states with reverse intersystem‐crossing (RISC) of k RISC = 0.6–21·10 9 s −1 , quantum yields of up to 0.8 and k TADF of 0.8‐1.9·10 6 s −1 that are among the fastest for Cu I emitters, outcompeting traditional triplet emitters based on Ir III and Pt II as well as organic deep red to near‐IR TADF emitters. While yellow to red emission is observed in single crystals, embedding the complexes into polymers or grinding shifts the luminescence into the deep red to near‐IR. The mechanochromism is due to disruption of C─H⋯π interactions between the ligands, reducing the energy gap between the ground state and 1/3 LLCT states. The Cu I iPC complexes bear potential for devices operating under electroluminescent conditions as demonstrated by a proof‐of‐concept deep‐red OLED application.

The cutouts of graphene sheets, particularly those with a nonplanar topology, present vast opportunities for advancement. Even a slight deviation from the planar structure can lead to intriguing (chiro)optical features for helically twisted nanographenes. In this context, we introduce two regioisomeric π-extended nanographenes that exhibit distinct excited-state characteristics. The helicene structure and the photophysical features can be easily tuned by changing the connecting position of the nanographene to the carbazole core (2,7− and 3,6−). Single-crystal X-ray diffraction analysis confirmed the formation of nanographenes with bent and helical conformations. Both derivatives exhibited thermally activated delayed fluorescence at room temperature and phosphorescence at low temperatures. Notably, the nanographene with the bent structure displayed an impressive red afterglow lasting over 30 seconds, in contrast to the very weak afterglow observed in the helical structure. DFT calculations revealed the existence of an isoenergetic higher triplet state (T 8 ) and comparatively weak spin-orbit coupling (T 1 -S 0 ), thereby enabling the bent nanographene to exhibit a long-lived component and strong afterglow. Our findings highlight the significance of regioisomeric nanographenes with exceptional optical properties and offer a deeper understanding of the structure–property relationship in nonplanar nanographenes.

Abstract Cyclic amino(alkyl) and cyclic amino(aryl) carbenes (cAACs/cAArCs) have been established as very useful ligands for catalytic and photonic applications of transition metal complexes. Herein, we describe the synthesis of a structurally related sterically demanding, electrophilic [2.2]isoindolinophanyl‐based carbene (iPC) that bears a [2.2]paracyclophane moiety. The latter leads to more delocalized frontier orbitals and intense green fluorescence of (HiPC)OTf ( 2 ) from an intra‐ligand charge transfer ( 1 ILCT) state in the solid state. Base‐promoted synthesis of the free carbene led to an unusual ring expansion and subsequent dimerization reaction, but the beneficial ligand properties can be exploited by trapping in situ at a metal center. The iPC ligand is a very potent π‐chromophore, which participates in low energy metal‐to‐ligand (ML)CT transitions in [RhCl(CO) 2 (iPC)] ( 4 ) and IL‐“through‐space”‐CT transitions in [Au(iPC) 2 ]OTf ( 5 ). The steric demand of the iPC leads to high stability of 5 against air, moisture, or solvent attack, and ultralong‐lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 5 , which outperformed other established photocatalysts in comparison.

Photoactive zinc(II) complexes typically undergo fluorescence from the singlet excited state as the dominant radiative pathway, as the operative spin-orbit coupling is usually very small and phosphorescence from the triplet state is strongly forbidden. Although dicationic zinc(II) tris(bipyridine) strictly follows this scheme with fluorescence at lambda(em) = 326 nm, constructing the ligand sphere as a hemicage was reported to lead to quantitative intersystem crossing (ISC) and subsequent fast phosphorescence with lambda(em) = 485 and a short radiative lifetime of ca. 1 mu s. Surprised by this finding, we reinvestigated [Zn(bpy)(3)](2+) and its hemicage derivative in great detail, including variable temperature and time-resolved photophysical measurements in solution and solid state as well as high-level theoretical calculations to resolve their excited state behavior. Our investigations suggest that both compounds undergo fluorescence at room temperature with significantly different radiative rate constants of k(r) = 2 x 10(8) and 1.2 x 10(6) s(-1), respectively, and only weak phosphorescence on the millisecond time scale at low temperatures. The major difference is the occurrence of additional charge-transfer states within the ligand scaffold of the hemicage, which accelerate the ISC to the (LC)-L-3(bpy) state from 350 s down to 82 ns and reduce the fluorescence rate constant.

AbstractLuminescent metal complexes based on earth abundant elements are a valuable target to substitute 4d/5d transition metal complexes as triplet emitters in advanced photonic applications. Whereas CuI complexes have been thoroughly investigated in the last two decades for this purpose, no structure‐property‐relationships for efficient luminescence involving triplet excited states from ZnII complexes are established. Herein, we report on the design of monomeric carbene zinc(II) dithiolates (CZT) featuring a donor‐acceptor‐motif that leads to highly efficient thermally activated delayed fluorescence (TADF) with for ZnII compounds unprecedented radiative rate constants kTADF=1.2×106 s−1 at 297 K. Our high‐level DFT/MRCI calculations revealed that the relative orientation of the ligands involved in the ligand‐to‐ligand charge transfer (1/3LLCT) states is paramount to control the TADF process. Specifically, a dihedral angle of 36–40° leads to very efficient reverse intersystem‐crossing (rISC) on the order of 109 s−1 due to spin‐orbit coupling (SOC) mediated by the sulfur atoms in combination with a small ΔES1‐T1 of ca. 56 meV.

Luminescent metal complexes based on earth abundant elements are a valuable target to substitute 4d/5d transition metal complexes as triplet emitters in advanced photonic applications. Whereas Cu(I) complexes have been thoroughly investigated in the last two decades for this purpose, no structure-property-relationships for efficient luminescence involving triplet excited states from ZnII complexes are established. Herein, we report on the design of monomeric carbene zinc(II) dithiolates (CZT) featuring a donor-acceptor-motif that leads to highly efficient thermally activated delayed fluorescence (TADF) with for Zn(II) compounds unprecedented radiative rate constants k(TADF) = 1.2x10^6 s^-1 at 297 K. Our high-level DFT/MRCI calculations revealed that the relative orientation of the ligands involved in the ligand-to-ligand charge transfer (1/3^LLCT) states is paramount to control the TADF process. Specifically, a dihedral angle of 36-40° leads to very efficient reverse intersystem-crossing (rISC) on the order of 10^9 s^-1 due to spin–orbit coupling (SOC) mediated by the sulfur atoms in combination with a small E(S1-T1) of ca. 56 meV (calc. 20 meV). In addition, the chiral carbene ligand leads to the generation of circularly polarized luminescence (CPL) with high dissymmetry values g(lum) of up to 3.3x10^-2 in polystyrene (PS).

A dimeric ZnII carbene complex featuring bridging and chelating benzene-1,2-dithiolate ligands is highly stable towards air and water. The donor-Zn-acceptor structure leads to visible light emission in the solid state, solution and polymer matrices with max between 577-657 nm and, for zinc(II) complexes, unusually high radiative rate constants for triplet exciton decay of up to kr = 1.5105 s-1 at room temperature. Variable temperature and DFT/MRCI studies show that a small energy gap between the 1/3LL/LMCT states of only 79 meV is responsible for efficient TADF. Time-resolved luminescence and transient absorption studies confirm the occurrence of long-lived, dominantly ligand-to-ligand charge transfer excited states in solution, allowing for application in Dexter energy transfer photocatalysis.

A series of chiral mechanochromic copper(I) cAAC (cAAC= cyclic (alkyl)(amino)carbene) complexes with a variety of amide ligands have been studied with regard to their photophysical and chiroptical properties to elucidate structure-property relationships for the design of efficient triplet exciton emitters exhibiting circularly polarized luminescence. Depending on the environment, which determines the excited state energies, either thermally activated delayed fluorescence (TADF) from (LLCT)-L-1/3 states or phosphorescence from 3LLCT/LC states occurs. However, neither chiral moieties at the carbene nor at the carbazolate ligands provide detectable luminescence dissymmetries g(lum). An exception is [Cu(phenoxazinyl)(cAAC)], showing orange to deep red TADF with lambda(max) = 601-715 nm in solution, powders and in PMMA. In this case, the amide ligand can undergo distortions in the excited state. This design motif leads to the first linear, non-aggregated CPL-active copper(I) complex with g(lum) of 3.4 . 10(-3) combined with a high radiative rate constant of 6.7 . 10(5) s(-1).

A dimeric ZnII carbene complex featuring bridging and chelating benzene-1,2-dithiolate ligands is highly stable towards air and water. The donor-Zn-acceptor structure leads to visible light emission in the solid state, solution and polymer matrices with max between 577-657 nm and, for zinc(II) complexes, unusually high radiative rate constants for triplet exciton decay of up to kr = 1.5105 s-1 at room temperature. Variable temperature and DFT/MRCI studies show that a small energy gap between the 1/3LL/LMCT states of only 79 meV is responsible for efficient TADF. Time-resolved luminescence and transient absorption studies confirm the occurrence of long-lived, dominantly ligand-to-ligand charge transfer excited states in solution, allowing for application in Dexter energy transfer photocatalysis.

Cyclopentadienyls are well-known strong donor ligands and have been successfully employed in catalysis as they tolerate a variety of substituents to adjust their steric and electronic properties. Although such highly modifiable ligands are of great interest for luminescence and photocatalytic applications, studies of CpR-containing photoactive transition-metal complexes are quite rare. In this work, we present a structural, electrochemical, and first elaborated photophysical investigation of a series of copper(I) half-sandwich complexes bearing cyclic alkyl(amino)carbenes (CAACs) as chromophore ligands and compare them with [Cu(Cp)(IDipp)] and [Cu(Cp*)(IDipp)] bearing a traditional N-heterocyclic carbene. Furthermore, we present the first molecular structure derived from single-crystal X-ray diffraction of a copper(I) indenyl complex, which can be described as an η2 (σ, π)-coordination. The CuI half-sandwich complexes show blue-green to orange phosphorescence with a photoluminescence quantum yield of up to 59% and radiative rate constants kr of up to 4 × 104 s-1 in the solid state, depending on the substitution pattern of the CpR ligand. Our TD/DFT calculations suggest that the emitting excited states are of 3MLCT/LLCT character. We determined the excited-state lifetime of the CuI half-sandwich complexes in solution to be as long as 600 ns, which in combination with the large π-surface of the CpR ligands allows for Dexter energy transfer for photocatalytic applications. In addition, the chiroptical properties of chiral [Cu(Cp/Cp*)(CAACMenthone)] were studied and compared to [CuCl(CAACMenthone)], of which we demonstrate that its circular polarized luminescence is the result of excimer formation and not, as previously reported, attributed to the monomeric C1-symmetric structure.

Nine different coinage metal (Cu, Ag) π complexes of diborenes with various anionic diborene (aryl, heteroaryl) and metal substituents (Cl, Br, C6F5, C2SiMe3), stabilizing neutral donors (N-heterocyclic carbene = NHC, phosphine), configurations (cis/trans, acyclic/cyclic diborene), and charges (neutral, cationic) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallographic analyses. Their optical properties were investigated by UV-vis absorption and steady-state as well as time-resolved luminescence spectroscopy in solution and the solid state to gain insights into the excited-state behavior of this unusual class of photoactive compounds and to provide structure-property relationships. The structural and electronic modification of the (B═B)···M motif greatly influences not only the visible light absorption but also the photostability and quantum yields, which can reach high values of up to f = 0.42. The lifetimes are found in the nanosecond regime, providing estimated radiative rate constants over a wide range of kr = 1.3-14 × 107 s-1, indicative of fluorescence. Intersystem crossing (ISC) is sufficiently slow for prompt emission from the S1 state to be observed, while the spin-orbit coupling in the T1 state is too weak for phosphorescence to occur at room temperature. ISC can be accelerated, however, by modifying diborene ligand substitution and the coinage metal center, hinting at the potential for exploiting the properties of long-lived triplet excited states of metal diborene complexes in the future.

The development of novel and operationally simple synthetic routes to carbene-metal-amido (CMA) complexes of copper, silver and gold relevant for photonic applications are reported. A mild base and sustainable solvents allow all reactions to be conducted in air and at room temperature, leading to high yields of the targeted compounds even on multigram scales. The effect of various mild bases on the N-H metallation was studied in silico and experimentally, while a mechanochemical, solvent-free synthetic approach was also developed. Our photophysical studies on [M(NHC)(Cbz)] (Cbz=carbazolyl) indicate that the occurrence of fluorescent or phosphorescent states is determined primarily by the metal, providing control over the excited state properties. Consequently, we demonstrate the potential of the new CMAs beyond luminescence applications by employing a selected CMA as a photocatalyst. The exemplified synthetic ease is expected to accelerate the applications of CMAs in photocatalysis and materials chemistry.

This book chapter highlights recent developments of luminescent linear two-coordinated d10 coinage metal complexes, which can show exceptional short radiative lifetimes for phosphorescence and TADF. Emission via the latter mechanism has led to radiative rate constants faster by a factor of 10 compared to state-of-art 5d emitters employed in OLEDs and have thus opened the door for future revolutions in terms of applications. In addition, new design criteria for highly efficient stimulus-responsive phosphorescence have been formulated. These exceptional photophysical properties are conceptually discussed in light of general photophysical principles, of which an overview is also presented.

Im Rahmen dieser Arbeit wurden lumineszente Kupfer(I)-verbindungen untersucht, um durch die Herstellung von Struktur-Eigenschafts-Beziehungen einen Beitrag zur Erforschung niederenergetischer Emitter und mechanoresponsiver Phosphoreszenzmaterialien zu leisten. Daruber hinaus wurden Vorarbeiten zur Ergrundung kooperativer Effekte in dinuklearen Kupfer(I)-komplexen durchgefuhrt. Im Bereich niederenergetischer Emitter wurden tetraedrische Kupferverbindungen mit Chromophorliganden auf Basis des Grundmotivs 2-(Pyridin-2-yl)-imdazol untersucht. Komplexe mit diesem Liganden emittieren meistens Grun bis Orange, daher wurde ein Stickstoffatom im Ruckgrat des Liganden durch Schwefel substituiert, um eine bathochrome Verschiebung zu bewirken. Zur Untersuchung des Einflusses der Donorstarke, Sterik und Komplexgeometrie auf das Emissionsverhalten wurden diverse Phosphane und ein NHC als Donorliganden verwendet. Die Emissionsmaxima der untersuchten Verbindungen liegen erwartungsgemas im Orangen bis Tiefroten und es konnten fur diesen Emissionsbereich gute Quantenausbeuten von bis zu 11 % erreicht werden. Die Anfalligkeit tetraedrischer Kupfer(I)-komplexe fur Verzerrungen im angeregten Zustand und die damit einhergehende Erhohung strahlungsloser Prozesse lies sich durch den Einsatz sterisch anspruchsvoller Liganden unterdrucken. Um das Potenzial fur die Verwendung in optoelektronischen Bauteilen zu ergrunden, wurden umfangreiche Stabilitatstests durchgefuhrt, die die enorme thermische Belastbarkeit im Festkorper sowie langfristige Stabilitat in verdunnter Losung einiger Verbindungen bestatigten. Ferner wurden in Kooperation mit der Gruppe um Prof. Holger Braunschweig photophysikalische Studien an zwei dinuklearen und einem trinuklearen Kupfer(I)-diborinkomplex durchgefuhrt, die im Rahmen der Promotionen von Dr. Jan Mies und Dr. Theresa Dellermann synthetisiert wurden. Die Verbindungen weisen in Festkorper und Losung tiefrote Phosphoreszenz auf. Die Effizienz des trinuklearen Komplexes (φ = 0.58 im Festkorper) ist deutlich hoher als die der beiden dinuklearen Verbindungen (φ < 0.03). Die Kupfer-Diborin-Bindung besitzt einen signifikanten kovalenten Anteil. Die Ubergangsmetallatome haben somit einen starken Einfluss auf die strahlenden Ubergange, was zum Auftreten von Phosphoreszenz fuhrt. Fur effiziente Emission ist eine lineare Anordnung zweier Kupferfragmente um das Diborin notwendig, was im Fall des trinuklearen Komplexes stets gewahrleistet ist, fur die dinuklearen Komplexe jedoch nur in Losung zu beobachten ist. Durch die Studien wurde einerseits das komplexe Emissionsverhalten dieser Komplexe aufgeklart und andererseits die Relevanz dieser neuen Verbindungsklasse fur niederenergetische Emittermaterialien gezeigt. Zusatzlich wurden Vorarbeiten zur Untersuchung kooperativer Effekte in dinuklearen Kupfer(I)-verbindungen unter Ausschluss schwer zu erhaltender cuprophiler Wechselwirkungen durchgefuhrt. Es sollten mono- und dinukleare Kupfer(I)-komplexe mit Bisbenzimidazol und Benzimidazolpyrimidin als verbruckenden Chromophorliganden synthetisiert und photophysikalisch untersucht werden, um eine eventuelle Erhohung der Effizienz der dinuklearen Komplexe gegenuber ihren mononuklearen Analoga zu quantifizieren. Im Rahmen dieser Arbeit gelang es, einen zuverlassigen Syntheseweg fur die im Ruckgrat alkylierten verbruckenden Liganden zu etablieren. Ferner wurden erste Versuche zur Herstellung kationischer und neutraler mononuklearer Komplexe durchgefuhrt. Auserdem wurde die mechanochrome Lumineszenz eines aus Vorarbeiten bekannten dinuklearen Kupferkomplexes untersucht und Struktur-Eigenschafts-Beziehungen hergestellt. Hierzu wurden Komplexsalze mit den Anionen PF6- und BF4- hergestellt und mittels zahlreicher Spektroskopiemethoden analysiert, um umfangreiche Informationen zu den Eigenschaften im Grund- und angeregten Zustand zu sammeln. Durch Schwingungsspektroskopie wurde nachgewiesen, dass die Phasenanderung zu keiner veranderten Konstitution der Verbindung im Grundzustand fuhrt. Durch 1H-19F-HOESY- sowie 19F-Festkorper-NMR-Experimente wurde festgestellt, dass sowohl in Losung wie auch im Festkorper Kation und Anion gepaart vorliegen und miteinander wechselwirken. Da die BF4- und PF6-Komplexe in Losung ein sehr ahnliches Emissionsverhalten zum amorphen Feststoff aufweisen, wurde davon ausgegangen, dass die fur die Emission verantwortlichen Strukturen in beiden Medien vergleichbar sind. Zusatzlich gelang es, mittels ESR-Spektroskopie nachzuweisen, dass im Grundzustand keine ausreichende Annaherung der beiden Kupferatome stattfindet, um dipolare Wechselwirkungen zu erzeugen. Mithilfe quantenchemischer Rechnungen wurde die mechanochrome Lumineszenz nicht auf das Auftreten von Cuprophilie zuruckgefuhrt, sondern auf die Ausbildung einer Cu-F-Bindung im angeregten Zustand, was ein vollig neuer Mechanismus fur mechanochrome Lumineszenz bei Kupfer(I)-komplexen ist. In weiterfuhrenden photophysikalischen Studien wurde zudem gezeigt, dass die Emission auch Empfindlichkeit gegenuber Temperatur sowie Losungsmitteldampfen aufweist und es sich somit um eine multiresponsive Verbindungsklasse handelt.

A set of mono- and dinuclear Au-I and Ag-I alkynyl complexes bearing the carba-closo-dodecaboranylethynyl ligand show intense room temperature phosphorescence. The {closo-1-CB11} cage participates in an unprecedented way as an electron donating moiety, changing the direction of the charge-transfer excited state.

A series of easily accessible linear N-heterocyclic carbene (NHC) copper(I) complexes, bearing pyridine (py) and its derivatives as chromophore ligands, are barely emissive in the single-crystalline solid state. However, their powders, neat films, and dilute doped films of poly(methyl methacrylate) (PMMA; 1-10%) show very intense blue-to-blue-green photoluminescence with remarkable quantum yields φ of up to 87% and microsecond lifetimes, indicative of triplet states being involved. These luminescence properties are similar to trigonal coordinated NHC copper(I) bis(pyridine) complexes, which we have also isolated and characterized with respect to their structures and photophysics. Our spectroscopic and theoretical studies provide detailed insight into the nature of the luminescence enhancing effect of the linear two-coordinated copper(I) compounds, which is based on the formation of Cu-F interactions between the BF4- anions and [Cu(NHC)(2-R-py)]+ (R = H, Me, Ph) cations. These interactions are absent in the single crystals but lead to a distorted ground-state structure in the precipitated powders or in PMMA films, giving rise to high kr. In addition, we found that our linear copper(I) complexes exhibit mechanochromic luminescence because grinding of the single crystals leads to enhanced emission intensity. In light of the recently reported cation-anion contact-induced mechanochromic luminescence of two-coordinated copper(I) complexes, this study supports the generality of this new mechanism for the design of mechanoresponsive phosphorescent materials.

AbstractDie mechanistische Untersuchung von mechanochromer Lumineszenz ist sehr wichtig zur Entwicklung von Materialien für die Sensorik, Datenspeicherung oder Lumineszenzschalter. Die strukturelle Ursache in phosphoreszierenden Systemen ist selten bekannt und somit die Aufstellung von Struktur‐Eigenschafts‐Beziehungen eine große Herausforderung. Für d10‐Münzmetallkomplexe wurden Änderungen der M‐M‐Wechselwirkungen als Hauptmechanismus vorgeschlagen. Wir zeigen mit einer mechanisch induzierten, reversiblen Kation‐Anion‐Exciplexbildung, basierend auf Cu‐F‐Interaktionen, einen neuen Mechanismus, der zu sehr effizienter mechanochromer Phosphoreszenz mit für CuI‐Komplexe ungewöhnlich weiten Emissionsverschiebung von UV‐blau zu gelb führt. Die gelbe Lumineszenz ist thermo‐ und vaporesponsiv, wodurch sowohl Weißlicht als auch die ursprüngliche UV‐blaue Emission generiert werden können.

The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure-property relationships remains challenging. Changes in the M-M interactions have been proposed as the main mechanism with d10 coinage metal compounds. Herein, we describe a new mechanism-a mechanically induced reversible formation of a cation-anion exciplex based on Cu-F interactions-that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV-blue to yellow for CuI complexes. The low-energy luminescence is thermo- and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV-blue emission.

Herein are reported the first π-complexes of compounds with boron-boron triple bonds with transition metals, in this case CuI. Three different compounds were isolated that differ in the number of copper atoms bound to the BB unit. Metalation of the B-B triple bonds causes lengthening of the B-B and B-CNHC bonds, as well as large upfield shifts of the 11B NMR signals, suggesting greater orbital interactions between the boron and transition metal atoms than those observed with recently published diboryne/alkali metal cation complexes. In contrast to previously reported fluorescent copper(I) π-complexes of boron-boron double bonds, the Cun-π-diboryne compounds (n = 2, 3) show intense phosphorescence in the red to near-IR region from their triplet excited states, according to their microsecond lifetimes, with quantum yields of up to 58%. While the Cu diborene bond is dominated by electrostatic interactions, giving rise to S1 and T1 states of pure IL(π-π*) nature, DFT studies show that the CuI π-complexes of diborynes reported herein exhibit enhanced metal d orbital contributions to HOMO and HOMO-1, which results in S1 and T1 having significant MLCT character, enabling strong spin-orbit coupling for highly efficient intersystem-crossing S1 → Tn and phosphorescence T1 → S0.

Herein, we report on the synthesis and structural characterization of a series of trigonal and tetrahedral cationic copper(I) complexes, bearing phosphine or N-heterocyclic carbene ligands as donors, with benzthiazol-2-pyridine (pybt) and benzthiazol-2-quinoline (qybt) acting as π-chromophores. The compounds are highly colored due to their 1MLCT (MLCT = metal-to-ligand charge transfer) states absorbing between ca. λabs = 400-500 nm, with 1ILCT (ILCT = intraligand charge transfer) states in the UV region. The relative shifts of the S0→S1 absorption correlate with the computed highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, the qybt complexes generally being lower in energy than the pybt ones due to the larger conjugation of the quinoline-based ligand. The compounds exhibit, for CuI complexes, rare intense long-lived near-IR emission with λmax ranging from 593 to 757 nm, quantum yields of up to Φ = 0.11, and lifetimes τ of several microseconds in the solid state as well as in poly(methyl methacrylate) films. Although a bathochromic shift of the emission is observed with λmax ranging from 639 to 812 nm and the lifetimes are greatly increased at 77 K, no clear indication for thermally activated delayed fluorescence was found, leaving us to assign the emission to originate from a 3(Cu→pybt/qybt)MLCT state. The red to near-IR emission is a result of incorporation of the sulfur into the chromophore ligand, as related nitrogen analogues emit in the green to orange region of the electromagnetic spectrum. The photophysical results and conclusions have further been corroborated with density functional theory (DFT)/time-dependent DFT calculations, confirming the nature of the excited states and also the trends of the redox potentials.