Reactivity and photochemistry of copper halide complexes

Abstract: This paper deals with 3-picoline, 4-picoline, 3,4-lutidine and 3,5-lutidine complexes of copper(I) iodide (CuI(3-pic), CuI(4-pic), CuI(3,4-lut) and (CuI(3,5-lut)). The experimental investigation was divided into several parts. Firstly, the synthesis and characterization of the compounds both as powder and as thin films. Secondly, the photoluminescence study. Thirdly, the observation of ligand exchange reaction by vapor diffusion, and lastly, the determination of the lifetime by time-resolved photoluminescence of respective compound.  All studied copper(I)-iodide-substituted pyridine compounds were emissive both as powders and thin films. The synthesis of the tetranuclear cluster powders yields both cluster and polymeric forms of structure. The pXRD of the powders CuI(3-pic), CuI(4-pic), and CuI(3,5- lut) confirmed to be as polymeric structures, hence the CuI(3-pic) showed thermochromism behavior. The structure of CuI(3,4-lut) is still unconfirmed. The most effective method for the synthesis of the thin films was the SILAR method.  The photoluminescence spectra of respective thin films differ from their corresponding powders, and the structure of the compounds as thin films is yet unexplored. The emission of CuI(3-pic), CuI(4-pic), and CuI(3,4-lut) as thin films were similar 480nm, hence the emission of CuI(3,5-lut) thin film lays on 518 nm. Therefore, the ligand exchange reaction was performed on the CuI(3-pic) thin film with 3,5-lutidine as the exchanging ligand.  The ligand exchange reaction of CuI(3-pic) thin film by vapor diffusion of 3,5-lutidine results in a spectrum shift from the emission spectrum of CuI(3-pic) to the spectrum of CuI(3,5-lut). This indicates a successful ligand exchange reaction by vapor diffusion.  The lifetimes of the investigated compounds which have their best fit of mono-exponential function were between 2,2 μs and 9,52 μs. The lifetimes were determined on the thin films with time-resolved photoluminescence. The ligand exchange reaction was also observed by time- resolved photoluminescence which reveals some stable lifetimes during the reaction that can indicate the formation of intermediates. In contrast, the measured lifetimes during the ligand exchange reaction have their best fit of bi-exponential function which can be due to reaction conditions during the measurement or the homogeneity of the thin films.