Lightning Up the Structural Complexity: Challenging Bromine’s ‘Heavy’ Reputation in Fluorescence Properties of Organic–Inorganic Hybrid Materials with 5,7-Dichloro-8-Hydroxyquinolinium

Abstract

This study details the synthesis and characterization of a series of organic−inorganic hybrid materials (OIHMs) based on 5,7-dichloro-8-hydroxyquinolinium cations combined with open-shell [Fe(III), Cu(II)] as well as closeshell [Zn(II), Cd(II), Hg(II), Sn(IV)] halogenometalate anions, showcasing diverse geometries and complex intermolecular interactions. The study revealed a definite correlation between fluorescence characteristics and the associated structural and electronic factors, among which the presence of water molecules instigated fluorescence quenching. In the case of mercury-based compounds, a notable enhancement in fluorescence was linked to a reduced quantity of water within the crystal lattice, leading to fewer water-mediated interactions and consequently increased fluorescence. Surprisingly, bromides exceeded chlorides in terms of fluorescence intensity, a result credited to anion-π interactions and halogen-water interactions. This research highlights the substantial role these interactions play, offering invaluable insights into fluorescence-based technologies. Moreover, it underscores the necessity for a comprehensive understanding of the structural and electronic elements in relation to the fluorescence properties.