| In this paper,we proposed the possibility of conjugated π bridge hemicyanine dye for ultraviolet photoabsorber,and the energy relaxation mechanism was analyzed.In addition,the ultraviolet protection performance was also tested.The theory and steady absorption spectra of hemicyaines were measured by a combination of density functional theory and experimentation.The ultraviolet absorption spectra showed that all the hemicyanine dyes had good absorption intensity in the UVR region,which was in line with the precondition of using the compounds as ultraviolet photoabsorbers.The potential energy surfaces(PESs)of different electronic states of hemicyanine dyes were constructed by linear interpolation internal coordinate method(LIIC).All hemicyanine molecules have conical intersection points with the ground state and the first electron excited state as the configuration angle approaches 90°.At this point,the molecules in the excited state can be nonadiabatic relaxed ultrafast to the ground state and trans-cis photoisomerism occurs,which indicates that these molecules are suitable as ultraviolet photoabsorbers.Furthermore,we studied the excited state properties and energy relaxation pathways of these hemicyanine molecules by femtosecond transient absorption spectroscopy.The fitting excited state lifetime shows that the relaxation process of these molecules is at ultrafast level,and this class of molecules has great potential as ultraviolet photoabsorbers.In addition,we tested the ultraviolet absorption intensity of1,3-Diphenylisobenzofuran(DPBF)protected by hemicyanine dyes with the duration of ultraviolet irradiation and compared with other common ultraviolet photoabsorber.The results showed that the absorbance of DPBF solution protected by hemicyanine dyes decreased with irradiation time significantly lower than that of the group protected by cinnamic acid,which not only proved that hemicyanine dyes are excellent ultraviolet photoabsorber molecules. |
PDF Full Text Request