Photoisomerization in 5-(benzylidene) -2,4-thiazolidinedione family: A TD-DFT quantum chemical study

In this work, the study of the photochemical isomerization Z→E in 5-(benzylidene)-2,4-thiazolidinedione family (HTZD, TFTZD) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(d,p) level of theory. The potential energy surfaces at ground and excited states, structural parameters, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant and dipole moment were calculated. Ground state calculations show that the energies of E form of HTZD and TFTZD molecules are greater than corresponding Z forms by 5 and 4.4 kcal mol-1, indicating that Z forms are more stable than E ones. Comparison of the f values of molecules shows that the intensity of fluorescence emission for HTZD is smaller than TFTZD.