The excited-state lifetime of many molecules is known to strongly shorten in protic solvents. In some cases, this is due to the occurrence of excited-state proton transfer with solvent molecules and a proton-transfer product can be easily identified. In other cases, no evidence of proton transfer is observed and the excited state apparently decays non-radiatively to the ground state without the involvement of any intermediate state. For example, the excited-state lifetime of eosin B decreases from 300 to 4 ps by going from decanol to water.1 On the other hand, that of eosin Y, that has two bromine atoms instead of nitro groups, amounts to several nanoseconds, independently of the solvent. This hydrogen-bond assisted non-radiative decay also plays a crucial role in the function of molecules such as kynurenines, that act as UV filters in the lens of the human eye.2We will present our investigations on the origin of this mechanism using various ultrafast spectroscopic techniques, including transient vibrational absorption spectroscopy.Molecules undergoing this deactivation can serve as powerful probes of the hydrogen-bond donating properties of their environment. We have applied this idea to liquid/water interfaces. The excited-state dynamics of such probes adsorbed at an interface was measured by time-resolved surface second harmonic generation,3and compared with that in bulk solutions. In all cases investigated, the interfacial dynamics was found to be slower than in bulk water by several orders of magnitudes, pointing to a very different hydrogen bond donating ability of interfacial water.1) Fita, P.; Fedoseeva, M.; Vauthey, E., J. Phys. Chem. A 2011, 115, 2465.2) Tsentalovich, Y. P.; Sherin, P. S.; Kopylova, L. V.; Cherepanov, I. V.; Grilj, J.; Vauthey, E., Investigative Opththalmology & Visual Science 2011, 52, 7687.3) Fedoseeva, M.; Richert, S.; Vauthey, E., Langmuir 2012,  28, 11291.

Hydrogen-bond assisted non-radiative decay in solutions and liquid/liquid interfaces

248th National Meeting (2014)

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