We carried out a comparative study on the excited-state properties of tetracene, which is prone to singlet fission, and its 2,2′ditetracene derivative to analyze the dependence of such loss channels on molecular packing and, thus, intermolecular interactions. In neat single crystals, the absorption and emission spectra of 2,2′-ditetracene are significantly red-shifted by about 150 meV from those of tetracene, while in the case of isolated molecules dispersed in crystalline anthracene matrixes, both dyes show virtually identical emission patterns. Unlike tetracene, the absence of delayed fluorescence in 2,2′-ditetracene single-crystal photoluminescence (PL) and timedependent density functional theory (DFT) calculations based on experimental single-crystal structures indicate a decline in the excited singlet-state energy below the E(S 1 ) = 2E(T 1 ) threshold. Simultaneously, time-resolved temperature-dependent PL data reveal an interplay of the molecular S 1 state and an excited dimer state, which is efficiently populated above 10 K. Upon cooling, the photoluminescence of 2,2′-ditetracene crystals outperforms that of tetracene by more than an order of magnitude and highlights the potential of molecular design, here the covalent linking of two tetracenes, to conserve the optical properties of the individual chromophores while decisively improving their photophysical properties in the crystalline aggregate.

Molecular near-IR (NIR) triplet-state emitters are of importance for the development of new, organic-electronics-based telecommunication technologies as optical fibers operating in the corresponding spectral bands allow for data transfer over much longer distances due to the significantly lower attenuation. However, achieving such low-energy triplet excited states with good radiative rate constants is very challenging, and studies regarding the single-photon emission of organometallics in this energy range are scarce. We have prepared a series of trigonal CuI CAAC complexes bearing chelating ligands with O, N, S, and Se donor atoms and studied their photophysical properties in this context. The compounds show weak low-energy absorption in solution between 400 and 500 nm due to mixed Cu → CAAC 1MLCT/LLCT states, resulting in yellow-green to orange appearance, which we have also correlated to the 15N NMR resonances of the π-accepting carbene ligand. In the solid state, phosphorescence from dominant 3(Cu → CAAC) CT states is observed at room temperature. The emission of the complexes is bathochromically shifted in comparison to structurally related linearly coordinated copper­(I) CAAC complexes due to structural reorganization in the excited state to a T-shape. For [Cu­(dbm)­(CAACMe)], the broad phosphorescence with outstanding λmax = 760 nm tailors out to ca. 1100 nm and leads to its proof-of-concept application as a nonclassical single-photon light source, constituting key functional units for the implementation of tap-proof data transfer.