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

Abstract

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 (TD-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 photo-induced electron transfer quenching in which Cu(I) is oxidized to a non-luminescent Cu(II) with capture of the halogen by a neighboring SCN ligand on the adjacent coordination polymer chain.

Alkyl Pyridinium Iodocuprate(I) Clusters: Structural Types and Charge Transfer Behavior

“…Evidence of charge transfer can also be seen in the excitation spectra of 8 and 9 which contain sharp peaks between 450 and 500 nm. These sharp peaks are uncharacteristic of halo- and pseudohalocuprate complexes, for which excitation spectra are typically smooth and broad. ,,, The maximum emission peak energy is independent of the choice of cation and is relatively unchanged between complexes. Thus, we assign the remaining maximum emission band to an XMCT within the iodocuprate cluster.…”

Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks

“…As previously mentioned, our group reported extensively on the optical memory of d 10 cyanometallates [16,17,23,30,82]. In many of these cases the optical memory behavior is the result of a photo-induced electron transfer [18,24,82].…”

“…Researchers continue to be attracted to copper(I) based coordination polymers which display a number of desirable photophysical behaviors including high emission quantum yields [1], emission energy tunability [2,3,4,5], thermally activated delayed phosphorescence [6,7,8], photochromism [9], thermochromism [10,11,12], vapochromism [13,14,15], and optical memory [16,17]. Most recently we have been interested in the optical memory behavior of these materials [16,18]. Materials that display optical memory are able to undergo a reversible change in emission upon laser irradiation such as reduction in emission intensity.…”

“…The mechanism by which optical memory occurs is difficult to predict and is dependent on a number of variables including chemical composition and structure [16,17,19,20,21,22,23]. For example, CuSCN(3-BrPy) 2 (3-BrPy = 3-bromopyridine) is composed of 1D metal/thiocyanate chains decorated with halopyridine ligands [4,16]. This complex exhibits luminescence behavior through a metal thiocyanate-to-pyridine charge transfer whereby yellow emission is observed at 538 nm.…”

Synthesis, Crystal Structures and Properties of Polymorphic and Isomeric Nickel(II)thiocyanate Coordination Compounds with 3‐Bromopyridine as Coligand

“…[45] In the course of our systematic investigations on thiocyanate coordination compounds we became interested in Ni-(NCS) 2 compounds with 3-bromopyridine as coligand, for which only some structures with Cd, Zn and Cu are reported in the Cambridge Structural Database. [47][48][49][50][51] Despite the formation of several discrete complexes, we obtained two different chain compounds, of which one contains the usual linear chains with an all-trans coordination, whereas the second compound consists of corrugated chains and a structure, which is very similar to that of Ni(NCS) 2 (4-(boc-amino)pyridine) 2 • CH 3 CN. Here we report on our investigations.…”