Synthesis of novel symmetrical alkylated phenyltetrazol-based 1,3-diynes and their structure-properties relationship

This study describes the synthesis and characterization of novel π-conjugated compounds based on 1,3-diynes containing an alkylated tetrazole moiety. Optical properties were characterized by UV–Vis absorption and fluorescence emission spectrophotometry, showing absorption in the ultraviolet region with a molar absorption coefficient of approximately 104 M−1 cm−1, ascribed to 1π-π* electronic transitions. The compounds were fluorescent in the region of 357–417 nm, with low quantum yields of approximately 2%. The fluorescence decay curves could be fitted by a single exponential decay with good χ2 values. All compounds presented in solution enhancement of light emission upon aggregation followed by bathochromic shifts, which could be related to aggregation-induced emission enhancement (AIEE) phenomenon. In the solid state, the alkyl groups played a significant role in the observed photophysical properties of the compounds, favoring π-stacking interactions between the fluorophoric groups. Theoretical calculations and photophysical results indicate the absence of charge transfer in these compounds. The redox behavior of the diyne compounds was examined using cyclic voltammetry (CV), which showed an irreversible oxidation process (at more positive potentials) and an irreversible reduction process (at more negative potentials). The values of the onset potentials were used in the calculation energies of HOMO (−5.72 to −5.85 eV), LUMO (−2.49 to −2.61 eV), and electrochemical bandgap (∼3.2 eV). Thermal and mesomorphic characterization was performed by TGA, DSC, and MOLP, which showed good thermal stability and liquid-crystalline properties. The theoretical calculations corroborated the absence of ICT in the excited state.