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

Abstract 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 1H NMR, 13C 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-l 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-l and 9a-k were calculated from their UV–vis data. The band gap of compounds 6a-l 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.