Chemistry Department Seminar

Sum Frequency Generation (SFG) has been utilized to investigate structure and dynamics of molecules at the air/water interface. The talk includes two parts. The first part is acid-base reaction at the air/water interface. We demonstrate that phenol as well as organic ion-phenolate can stay at the air/water interface. The pKa of phenol is higher than that in bulk. In the second part, molecular motion and electron transfer at the air/water interface will be introduced. With SFG the time dependent changes in the orientational motions of vibrational chromophores in interfacial molecules are obtained. The chromophores are the carbonyl group and the CF3 group, both in the coumarin 153 molecule at the interface. The orientational relaxation time of the C=O axis is slightly faster than that of the CF3 axis, with both however being much faster than that of the orientational relaxation of the coumarin molecules permanent dipole moment axis with respect to the surface normal. These interfacial results are compared with our measurements of the orientational relaxation of C153 in bulk water. The dynamics of excited state electron transfer at the air/water interface between photoexcited coumarin 314 (C314) serving as the acceptor and Dimethyl-aniline (DMA) as the donor, using the SFG probe that is resonant with the carbonyl chromophore of C314. The dynamics are compared with bulk electron transfer dynamics will be presented.