Chiang Mai Journal of Science

     A comprehensive study of the photophysical properties of three thiophene-based heterocyclic chalcones was investigated on the basis of joint optical spectroscopic technique and quantum chemical calculations. Three thiophene-based heterocyclic chalcone derivatives with 2,4,5-methoxy (2,4,5-OMe@Chal), 2,4,6-methoxy (2,4,6-OMe@Chal) and 3,4,5-methoxy (3,4,5- OMe@Chal) as terminal groups were focused. The thiophene-based heterocyclic chalcone, 2,4,5- OMe@Chal, 2,4,6-OMe@Chal and 3,4,5-OMe@Chal were synthesized, producing in 87%, 85% and 89% yields, respectively. The photophysical properties were performed by UV-Vis absorption and fluorescence spectroscopic technique. The obtained results indicated that the position of methoxy substituent groups brings to increasing in the fluorescence quantum yield (Фfluo). All the chalcone derivatives exhibit slightly low fluorescence quantum yields (Фfluo=0.0051-0.0518). In addition, Density Functional Theory (DFT) at PBE0/6-311G(d,p) level were successfully used to evaluate the molecular geometries, the characteristics of the excited singlet and triplet states. The calculated results were in well agreement with the experimental data, and indicated that the low fluorescence of 2,4,6-OMe@Chal and 3,4,5-OMe@Chal is derived from, not only intersystem crossing but also internal conversion due to the proximity effect. Among the three derivatives, it was found that 2,4,5-OMe@Chal shows higher fluorescence quantum yield than the others. This work deepens the understanding of thiophene-based heterocyclic chalcone derivatives and provides novel materials for improved fluorescence efficiencie