Figure-6: TD-DFT calculated UV-Vis spectra of D1, D1A, D2, D2A, D3 and D3A (a) in Methanol and (b) in Water by using SCC-DFTB
In order to get the understanding of the behavior of dyes in different solvents of varied polarity, the absorption spectrum of all dye were studied in methanol and water using TD-DFT at SCC-DFTB level of theory by utilizing parameters set org/tiorg-0-1 and solute factor of 2.7. The UV-Vis spectra calculated for all the dyes in methanol and water solvents is given in figure 6. The analysis exhibited a red shift in spectral peaks as the polarity of solvent is increased which depends upon properties of solvents and hydrogen bonding between solvent-solute and solute-solute molecules [42, 79, 80]. The amount of solvent has also affected the oscillator strength in addition to excitation energy of the photoactive species.