Femtosecond Spectroscopy and Quantum Chemistry of a Linearly Coordinated Copper(I) Carbene Complex

Abstract

Linearly coordinated copper(I) carbene complexes, such as [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]‐(2‐picoline)copper(I) tetrafluoroborate (1), exhibit promising photophysical properties with regard to organic light emitting diode (OLED) applications. Their emission characteristics strongly depend on the surrounding (crystal, matrix, and solution). Here, the behavior of 1 in solution is scrutinized by steady state as well as femtosecond spectroscopy. In coordinating solvents, like acetonitrile and alcohols, 1 is shown to bind solvent molecules as ligands. In non‐coordinating solvents, femtosecond UV/Vis absorption spectroscopy reveals a tri‐exponential decay with time constants of 0.3 ps, 900 ps, and 0.7 μs. The time constants are assigned with the aid of quantum chemistry. A more complex decay is observed in coordinating solvents.

How to tune luminescent Cu(i) complexes with strong donor carbenes towards TADF?

“…Thus, this linear 4-formylpyridine Cu(I) complex with an anionic donor carbene could be considered an ideal candidate for an efficient TADF emitter if it were not for the known problem that sterically unprotected electron-deficient Cu centers are susceptible to bond formation with additional coordinating molecules. 12,25,26,41,42 To prevent the accidental formation of trigonal complexes, we introduced methyl groups in ortho-position of the pyridine ring which increase the steric demand of the ligand, yielding the linear lutidine and 4-formyllutidine complexes 2a and 2b, respectively. 43 An alternative approach to increase the ''pull'' effect is the introduction of a second acceptor ligand resulting in the bis(formylpyridine) complex 3b, for which lower energies of the LLCT and MLCT states in comparison to the LC states are calculated (Fig.…”

Luminescent Copper(I)‐Complexes with an Anionic NHC obtained via a Coordination Polymer as Versatile Precursor**

“…In addition, the n π*‐type excitation on the formylpyridine is energetically accessible in the wavelength region above 300 nm. The local ππ* transition on the pyridine ring is known to peak at about 260 nm [20] . According to the calculations, the narrow band in the excitation spectrum of the linear complex 2 a is dominated by a strong LC(carbene) transition at about 350 nm and a weaker MLCT transition at about 330 nm.…”

“…The local ππ* transition on the pyridine ring is known to peak at about 260 nm. [20] According to the calculations, the narrow band in the excitation spectrum of the linear complex 2 a is dominated by a strong LC(carbene) transition at about 350 nm and a weaker MLCT transition at about 330 nm. LLCT transitions do not play an important role in this compound.…”

Luminescent Copper(I)-Complexes with an Anionic NHC obtained via a Coordination Polymer as Versatile Precursor

“…The photophysical parameters are compiled in Table 2. nm [ 20] . According to the calculations, the narrow band in the excitation spectrum of the linear complex 2a is dominated by a strong LC(carbene) transition at about 350 nm and a weaker MLCT transition at about 330 nm.…”