Light-Induced Photochemical Changes in Copper(I) Thiocyanate Complexes Decorated with Halopyridines: Optical Memory Manifestation

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We report on the photoluminescence of {CuSCN(3-XPy)2}n crystals (X = Br, Cl; Py = pyridine). Laser excitation at 266 nm for CuSCN(3-BrPy)2 at 78 K results in a decrease in the luminescence intensity with increasing irradiation time. Heating the sample to 298 K and recooling to 78 K results in recovery of the original luminescence intensity, hence manifesting an optical memory effect. Laser irradiation at longer or shorter wavelengths fails to produce a reduction in emission intensity. Interestingly, CuSCN(3-ClPy)2, despite being isomorphic, does not undergo emission intensity changes regardless of laser irradiation wavelength variation. Density functional theory (DFT) and time-dependent DFT calculations were performed on an adjacent chain model to explore the photochemical change that occurs upon laser irradiation. The observed reduction in luminescence intensity is attributed to photoinduced electron transfer quenching in which Cu(I) is oxidized to a nonluminescent Cu(II) with capture of the halogen by a neighboring SCN ligand on the adjacent coordination polymer chain.

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The Journal of Physical Chemistry C, v. 121, issue 45, p. 25430-25439