Synthesis and intriguing single-component white-light emission from oxadiazole or thiadiazole integrated with coumarin luminescent core

Abstract

There has been evidence of non-typical fluorescence activities in thiadiazole and oxadiazole derivatives. Also, some coumarin compounds with tunable luminescence properties via controlling the molecular structure and its aggregation have been recently reported. As a result, our effort concentrated on integrating these moieties in order to improve the applicability of the target compounds through easy synthetic schemes. All the synthesized derivatives underwent extensive spectrum analysis, including NMR, FT-IR, and mass spectroscopy. DFT calculations, UV–visible, and luminescence spectroscopy were used to study the photophysical characteristics of three compounds having coumarin luminescent core integrated with the thiadiazole, oxadiazole, or hydrazinecarbothioamide. We found that manipulating the packing of a compound under specific conditions (e.g., the solid state or moderate solution concentration of compounds containing the heterocyclic substituent “thiadiazole or oxadiazole”) can trigger processes related to the way the molecules interact, resulting in the appearance of dual or multiple fluorescence bands that cover the full visible range. Additionally, we deduced that the intriguing white emission from a single component might be generated by modifying the degree of molecular aggregation to balance the relative band intensities at short and long wavelengths. Long-wavelength emission arises from aggregated molecules whereas short-wavelength emission results from single molecules. It is evident that this balance is feasible in both the solid form of the thiadiazole derivative and 1 × 10–5 mol L–1 solution of the oxadiazole derivative. Hence, this research proposes an easy method for creating the intriguing white-light emission from a single component.