Solid‐State Step‐Scan FTIR Spectroscopy of Binuclear Copper(I) Complexes

Abstract

The structure in the ground and excited electronic state of two binuclear Cu N-heterocyclic phosphine complexes that are promising for implementation in organic light-emitting diodes is investigated by a combination of the time-resolved step-scan FTIR technique and quantum chemical calculations at the DFT level of theory. In contrast to the usual application of step-scan FTIR spectroscopy in solution, the herein-presented analyses are performed in a solid phase, that is, the Cu complexes are embedded in a KBr matrix (KBr pellet). The application of solid-state time-resolved step-scan FTIR spectroscopy is of great importance for transition metal complexes, since their photophysical properties often change on moving from solid to dissolved samples. The efficient applicability of the solid-state step-scan technique in a KBr matrix is demonstrated on the chosen Cu reference systems on nano- and microsecond timescales with an excitation wavelength of 355 nm. By comparison with theoretical results, the structure of the complexes in the electronic ground and lowest-lying electronically excited state can be determined.

Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

“…To gain more insight into the geometries of the long‐lived excited states, we subjected KBr disks of [Cr(tpe) 2 ][BF 4 ] 3 to time‐resolved step‐scan FTIR spectroscopy in the energy range of 1750 to 1200 cm −1 at 290 and 20 K (Figure a). The negative bands in the difference spectra indicate depopulation of the ground state while positive bands belong to the electronically excited state(s).…”

Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

“…Thei ncrease in emission intensity is compatible with the proposed diminished k nr (surface) at lower temperature of the "pseudo-Stokes shifted" 2 X g (D 3d ) state (Figure 3). [79] To gain more insight into the geometries of the long-lived excited states,w es ubjected KBr disks of [Cr(tpe) 2 ][BF 4 ] 3 to time-resolved step-scan FTIR spectroscopy [56][57][58]80] in the energy range of 1750 to 1200 cm À1 at 290 and 20 K ( Figure 5a). Thenegative bands in the difference spectra indicate depopulation of the ground state while positive bands belong to the electronically excited state(s).…”

Structural Characterization and Lifetimes of Triple‐Stranded Helical Coinage Metal Complexes: Synthesis, Spectroscopy and Quantum Chemical Calculations

“…Nowadays, large heterometallic complexes still lack thorough spectroscopic investigation, in comparison to the large number of investigations on mononuclear [1,2] and polynuclear homometallic [3,[4][5][6] complexes. Especially, heterometallic transition metal complexes are extremely demanding regarding high-level spectroscopic experiments, which is one reason there are so few examples found in the literature.…”

“…Yielding data of lifetimes in the nanosecond (ns) and microsecond (ms) time-range, the (TR) step-scan FTIR method is especially suited to investigate photophysical and photochemical processes in transition metal complexes, [17] such as photo-activated reactions, [17,18] or excitation and relaxation processes in electronic states. [2,[4][5][6][19][20][21] In combination with high level quantum chemical calculations, structural changes between different electronic states or different reaction states can be unveiled.…”

“…The TR-FTIR investigations have been performed using the sample in its solid form embedded in a KBr-matrix. This technique, presented first by Palmer et al [20] and established in the Gerhards group, [2,5,6,21] has several advantages for the investigation of transition metal complexes, for example, an extremely large spectral window, the pellets are almost oxygen free (without the need of the pump-freeze technique and the use of inert gas) and can be reused. Furthermore, this technique enables the measurement of complexes that have a poor solu-bility or dissociate in IR feasible solvents, as KBr is an interference-free matrix.…”