Síntese e caracterização de complexos polinucleares de cobre(I) para estudos de luminescência e termocromismo

Abstract

The use of luminescence can cover different areas for various purposes. In material chemistry, luminescent molecules form the basis for creating new optical devices such as OLEDs and WLEDs, as well as sparkling plastics and luminescent paints. The coordination chemistry of copper(I) has been extensively studied due to its rich results with organic and inorganic ligands, presenting numerous structural variations, ranging from simple mononuclear complexes to extensive coordination networks. Complexes based on copper(I)-iodide nanoclusters (Ncs) have attracted attention due to their emissive characteristics, as well as their ease of synthesis with different ligands, and excellent optical properties. These Ncs have organic ligands coordinated in polynuclear copper-iodide structures, which can exhibit various units. Among the most common are the tetrahedral cubane Cu4I4L4 and ladder polymers (CuxIxLx)n. The objective of this work is to synthesize and characterize a complex with a known tetrahedral cubane structure from the literature, Cu4I4Py4 (1, Py = pyridine), two novel complexes, Cu4I4TMX4 (2, TMX = 1,3,7-trimethylxanthine) and (CuITB)n (3, TB = 3,7-dimethylxanthine), as well as a coordination polymer PC-2b, in order to study their luminescent and thermochromic properties. The complexes were synthesized and characterized by PXRD, FT-IR, FAAS, TGA, luminescence studies using photoluminescence spectroscopy, XEOL, and thermochromism through photoluminescence studies at different temperatures Complex 3 and the PC-2b polymer also had their structures analyzed by SCXRD. Similar to complex 1, complex 2 exhibits thermochromism analogous to Ncs with a tetrahedral cubane structure, showing a high-energy band predominant at cryogenic temperature and a low-energy band predominant at room temperature, which can be attributed to the 3XLCT and 3CC charge transfer transitions, respectively. For complex 3, it was observed an infinite ladder (CuITB)n structure with hydrogen bonding between the crystal networks, explaining its greater thermal stability. Although it does not display thermochromism similar to complex 1, a rare luminescence with blue emission for ladder structures is observed, being more intense at cryogenic temperature. The PC-2b polymer presented a packing of two infinite ladder-type clusters, (CuITMX)n and (CuIMeCN)n, through weak hydrogen bond interactions. All three complexes exhibited radioluminescence at wavelengths similarly observed in photoluminescence, indicating that the emission is governed by the same charge transfer mechanisms as in photoluminescence.