Metal-free synthesis and characterization of 1,3-Bis(heteroaryl) benzenes followed by the photophysical studies using ultraviolet visible and fluorescence spectroscopy

A convenient approach for the synthesis of functionalized 1,3-bis(heteroaryl)benzenes 6 and 9 is describe via carbanion-induced ring transformation reaction of 6-heteroaryl-2H-pyran-2-ones 4 and 7. The ring transformation of 6-heteroaryl-2H-pyran-2-one 4 and 7 with heteroarylketones 5 and 8 was performed using KOH as base in DMF at ambient temperature. The ring transform products 6 and 9 were isolated in good to excellent yields under mild reaction condition. All the synthesized compounds were characterized by H-1 NMR, C-13 NMR, GCMS and IR followed by CHNS analysis. Additionally, the photophysical behaviour of the synthesized compounds was studied by using UV-vis and fluorescence spectroscopy. Compounds 6a-1 showed the emission maxima in the range of 411-461 nm while compounds 9a-k showed the emission maxima in the range of 437-508 nm. The band gap of synthesized compounds 6a-1 and 9a-k were calculated from their UV vis data. The band gap of compounds 6a-1 was obtained from 3.91 to 4.37 eV while 3.39-3.56 eV in case of the compounds 9a-k. Moreover, the thermo-gravimetric analysis (TGA) of compound 9f was carried out to check the thermal stability. (C) 2020 Elsevier B.V. All rights reserved.