Direct Observation of Mass Transfer at Solid−Liquid Interface by Laser Flash Photolysis of the Interface Probe Molecules

Abstract

Transient absorption signal delayed by a magnitude of 100 μs with respect to the exciting laser shot is observed after UV laser flash photolysis of degassed benzene, acetone, and acetonitrile solutions of an interface probe complex, i.e., gold(I) complex [{Au[P(C6H4OMe-p)3]}2-(μ-C≡C)] ([μ-ethynylene-bis{tris(4-methoxyphenyl)phosphine}gold]). Chemical reactions leading to the transient absorbance change are confirmed to be occurring at the solid−liquid interface, and the delay time is believed to arise from the photogenerated intermediate species in the bulk solution crossing the diffusion layer, which ultimately undergo interfacial reactions resulting in the observed transient absorbance change. The delay time is suggested as a direct measure for the thickness of the diffusion layer. The thickness of the diffusion layer around 0.2 μm, estimated by this method, is comparable to that from the sonovoltammetric study. Oscillations in transient absorbance kinetics are also observed, which can be attributed to the coupling between the interfacial chemical reactions and a photoacoustic effect; oscillation due to a single physical process arising from the schlieren effect under certain condition is also discussed. Similar transient phenomena are observed in another luminescent complex, i.e., a hexanuclear Cu(I) cluster Cu6(t-NS)6 (t-NS = 4-tert-butylpyridine-2-thiolate). The characterization of the photochemical reaction processes of the Cu(I) complex by means of transient absorbance difference spectra reveals that a consecutive biphotonic ionization process occurs after the laser flash. The intermediate species with a lifetime of 65 μs responsible for the interfacial reaction is tentatively assigned as a charge separation pair. A reaction scheme involving surface-assisted ionization of the charge separation pair is proposed to account for the coupling between the interfacial chemical reaction and the photoacoustic effect.

Carrier Recombination-Incited Substrate Vibrations after Pulsed UV-Laser Photolysis of TiO2 Thin Single-Crystal Plate and Nanoparticle Films

“…Accordingly, both the reflected or transmitted beams are deflected from their original directions; such a vibrational-induced beam deflection effect gives a sensitive probe for the local vibrations, similar to the reported light deflection caused by the photo-induced acoustic effect in the solution phase. 18,19…”

Time‐dependent density functional theory study on hydrogen‐bonded intramolecular charge‐transfer excited state of 4‐dimethylamino‐benzonitrile in methanol

“…Lippert tentatively ascribed the anomalous band to an intramolecular charge‐transfer (ICT) state, whose formation should be favored in polar solvents as compared to the less polar locally excited (LE) state giving rise to the normal band 3. The requirement to understand the nature of the ICT state has triggered a large number of experimental and theoretical studies 4–27. Since several mechanisms for the formation of the ICT state have been proposed, recent experimental and computational studies are predominantly in favor of the twisted intramolecular charge‐transfer (TICT) model 4–9.…”

“…Much more works concentrate on the determining the structures of the LE and ICT states,4–9 while the precise nature of the difference between the properties of the electronically excited state in protic and aprotic solvents is little understood. Hydrogen bonding in protic solvents can lead to complicated interactions, and thus may significantly influence the ICT state for DMABN in the protic solvents 10–65. Kowk et al have demonstrated and monitored the formation of a hydrogen‐bonded ICT state for the photoexcited DMABN in the protic solvent methanol (MeOH) using the time‐resolved infrared (TRIR) absorption spectra 61–63.…”

Surface-Binding Forms of Carboxylic Groups on Nanoparticulate TiO2Surface Studied by the Interface-Sensitive Transient Triplet-State Molecular Probe

“…A molecular probe capable of reporting its different environments has been widely employed in studying the interfacial process. It has been successful in the study of onset of the crystallization, the surface acidic sites of the zeolites, micropolarity in the reverse micelles, and mass transfer at a solid−liquid interface . Generally, this approach is to use the molecular spectral properties such as fluorescence, NMR, UV−visible absorption, time-resolved transient absorption, etc, to report its local environment, and is specific to each case studied.…”

“…It has been successful in the study of onset of the crystallization, the surface acidic sites of the zeolites, micropolarity in the reverse micelles, and mass transfer at a solid−liquid interface . Generally, this approach is to use the molecular spectral properties such as fluorescence, NMR, UV−visible absorption, time-resolved transient absorption, etc, to report its local environment, and is specific to each case studied. In our previous work, it has been found that when all- trans -retinoic acid (ATRA, Scheme ) is used to sensitize a TiO 2 colloid, , the photoinduced charge recombination between the injected electron and the oxidized dye cation follows a main channel of recombination to the triplet state which can be detected in a microsecond temporal range.…”