Capturing and Analyzing the Excited-State Structure of a Cu(I) Phenanthroline Complex by Time-Resolved Diffraction and Theoretical Calculations

Abstract

Time-resolved crystallography and density functional theory calculations are used to analyze the geometric and electronic changes that occur upon photoexcitation of [Cu(I)(dmp)(dppe)](+) in crystalline [Cu(I)(dmp)(dppe)][PF(6)] [dmp = 2,9-dimethyl-1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino)ethane]. In the pump-probe experiment, laser and X-ray pulses are synchronized to capture an image of the instantaneous molecular distortions in the transient triplet state. Parallel theoretical calculations, with the phenyl groups replaced by methyl groups, yield information on the distortion of the isolated cation and the change in electron density upon excitation. The experimental distortions are significantly less than the calculated values and are different for the two independent molecules in the asymmetric unit; these findings are attributed to the constraining influence of the crystal matrix. The calculations indicate that the electron transfer upon excitation is mostly from the dmpe ligand to the dmp ligand, while the Cu atomic charge changes by only approximately +0.1e, although the charge distribution on Cu is significantly affected. As found for homoleptic [Cu(I)(dmp)(2)](+), the change in the population of the Cu atom is close to the calculated difference between the corresponding Cu(II) and Cu(I) complexes. Charge density difference maps confirm these conclusions and show a large rearrangement of the electron density on the Cu atom upon excitation.

Thermal and photochemical control of nitro–nitrito linkage isomerism in single-crystals of [Ni(medpt)(NO2)(η2-ONO)]

“…A notable exception is the microsecond timeresolved study on [Cu(2,9-dimethyl-1,10-phenanthroline)(1,2-bis(diphenylphosphino)etane)][PF6] which shows that the two independent copper(I) centres distort to different extents upon photoactivation. 11 The differences were attributed to differences in the crystal environment of the two independent molecules. Thus, it is apparent that the molecular environment within the crystal is important in determining the level of conversion to the short-lived or metastable state.…”

Restricted Photochemistry in the Molecular Solid State: Structural Changes on Photoexcitation of Cu(I) Phenanthroline Metal-to-Ligand Charge Transfer (MLCT) Complexes by Time-Resolved Diffraction

“…1-2 As a first step towards time-resolved studies of structural changes occurring on photo-excitation of electron donors absorbed on nanoparticles, we have previously studied the excited state structure of the Cu(I) complex [Cu(I)(2,9-dimethyl 1,10-phenanthroline)(1,2-bis(diphenylphosphino)ethane)][PF 6 ] (1) by monochromatic time-resolved methods. 3 The complex of which the changes on excitation are described in the current article, [Cu(1)[(1,10-phenanthroline-N,N’) bis(triphenylphosphine) [BF 4 ] ( 2 ), lacks the dimethyl substitution which interferes with the expected flattening, and is therefore expected to undergo a larger rearrangement upon formal oxidation of the Cu(I) atom on photo-induced metal-to-ligand-charge-transfer (MLCT). 4-6 Cu(I) based chromophores have been proposed as promising and economically advantageous photosensitizers in photovoltaic cells.…”

Perspective: On the relevance of slower-than-femtosecond time scales in chemical structural-dynamics studies

“…Other studies involve intramolecular electron transfer (MLCT, metal-to-ligand charge transfer), in a number of highly luminescent Cu(I) dimethyl-phenanthroline photosensitizer complexes (Vorontsov et al , 2009; Makal et al , 2012). Such complexes are typical for use as light-emitting diodes (Armaroli et al , 2006; Yersin et al , 2011).…”