Síntese de tri-heterociclos pentadienos e estudo de suas propriedades luminescentes

Abstract

This study presents the synthesis of diois (1-4(a-h) and 5, Scheme 1), building blocks commonly used in designing and preparing heteroporphyrins. The synthesis of compounds 1 and 2 has been largely reported in the literature. On the other hand, there are few or no examples of synthetic routes for chalcogen-heteroaryl-substituted compounds such as 3 and 4 (Scheme 1), which constitutes a great challenge. Among the obtained products, thirty-seven molecules are new: five diols, thirty triheteropentadienylmethanes and two porphyrins. Chemical and structural characterization of the compounds 1-4(a-h), 5a and 6 were confirmed through a variety of analytical and spectroscopic techniques: High-Resolution Mass Spectrometry (HRMS), Nuclear Magnetic Resonance (NMR) by 1D and 2D, IR and UV spectroscopy. In addition, X-ray quality single-crystals of 3a allowed the determination of its relative stereochemistry as being (-)-RR-2,5-bis((4-methoxyphenyl)(thiophen-2yl)methyl)thiophene or (-)-SS-2,5-bis((4-methoxyphenyl)(thiophen-2-yl)methyl)thiophene. Unexpected fluorescence emission was observed when compounds triheteropentadienylmethanes were exposed to UV radiation, as shown in Figure 1. The photophysical studies of compounds 2a and 3a revealed a similar absorption profile, with the absorption bands in the violet-to-blue region (between 440-470 nm). Moreover, neither the distinct solvents (ACN, Dioxane, EtOH and CH2Cl2) nor the aryl-substituents (R, Scheme 1) nor the heteroatom (X, Scheme 1) affect significantly the HOMO-LUMO transition energy. In 2a, there is a dependence of the emission wavelength with the excitation wavelength. This fact may indicate that these compounds are examples of molecules exhibiting the non-traditional intrinsic luminescence phenomena.