Characterization and Spectroscopic Studies of the Morin-Zinc Complex in Solution and in PMMA Solid Matrix

Flavonoids, natural organic compounds from the polyphenolic group with broad bioactive and pharmaceutical properties, are strong ligands for many metal ions. This work describes the formation of the complex between Zn(II) and morin. The synthesized compound is characterized using three analytical techniques, i.e., ¹H NMR, IR, and thermal gravimetric analysis. Importantly, the complex was successfully obtained in the form of a solid, which enables its further physicochemical and structural characterization. Physicochemical characterization of the Morin-Zn complex was performed by steady-state and time-resolved spectroscopy. The absorption spectrum of the complex contains two main bands at ca. 407–415 nm and ca. 265 nm, and the complex emits yellow-green light with higher intensity than the free ligand. In the next step, morin and zinc complex were dispersed in a PMMA (poly (methyl methacrylate)) polymer matrix, and respective thin layers were produced. The studied thin films were deposited on silicon substrates by using the spin-coating method and characterized by X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM), Spectroscopic Ellipsometry (SE), UV-VIS spectroscopy, and photoluminescence (PL). The absorption of thin layers showed, similarly to solutions, the presence of two transitions: π→π* and n→π*, and a bathochromic shift for the morin-zinc complex compared to morin. The photoluminescence of the complex thin film showed two bands, the first in the range of 380–440 nm corresponding to PMMA, and the second with a maximum at 490 nm, derived from the synthesized compound.