The absorption and emission spectra of three azo\nsulfonamide compounds in different solvents were investigated\ntheoretically by using response functions combined with\ndensity functional theory (DFT), while the solvent effect on\nthe structure and the electronic transitions was determined\nusing the integral equation formalism for the polarizable continuum\nmodel (IEF-PCM). The results show that the applied\ndifferent exchange-correlation functionals can reproduce the\nexperimental values well. DFT calculations of the title compounds\nshowed that the H-bond formed between the solute\nand solvent molecules is one of the major causes of the\nreversible solvatochromism observed in measured spectra.\nThis is due to a better stabilization of the neutral\nform than the zwitterionic form in the polar protic solvents,\nwhich is characteristic of the hypsochromic shift.\nOn the other hand, the molecules considered exhibit a\nmonotonic behavior regarding the polarity of the lowlying\nexcited state (??gââ?¬â??CT) as a function of the solvent\npolarity. This dependence occurs in the case of the positive\nsolvatochromism and confirms the thesis regarding\nthe H-bond soluteââ?¬â??solvent interactions. Theoretically determined\nvalues of the two-photon cross section revealed\nthat the (?OF\n(2) ) shows similar trends with changes\nin ?abs, in contrast to ??OF? values. In conclusion, the\nresults demonstrate that the investigated molecules can\nbe used successfully as fluorochromes in bioimaging.
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