Photodimerization Kinetics of a Styrylquinoline Derivative in Langmuir–Blodgett Monolayers Monitored by Second Harmonic Generation

Abstract

To explore the influence of surface packing densities on the interfacial photochemical kinetics, the surface-selective second harmonic generation (SHG) technique was used to investigate the kinetics of two-photon induced [2 + 2] photocycloadditions of a styrylquinoline alkoxy derivative within the Langmuir−Blodgett (LB) monolayers. The laser power dependence experiment revealed that this interfacial photodimerization is a first-order reaction, which implies that the photoexcitation is the rate-limiting step. Interestingly, a comparison of photodimerization kinetics at different surface packing densities shows a nonmonotonic distribution of reaction rate constants, which can be attributed to a result of combined effects of the topochemical mechanism and steric hindrance. The atomic force microscopy measurements and theoretical calculations were also employed to help understand the [2 + 2] photocycloaddition mechanisms. The results presented in this work demonstrate that the surface packing density plays an important role in regulating the interfacial photoreactions within the LB monolayers composed of the conjugated aromatic molecular systems.

The Influence of Sodium Iodide Salt on the Interfacial Properties of Aqueous Methanol Solution by a Combined Molecular Simulation and Sum Frequency Generation Vibrational Spectroscopy Study

“…The orientations, conformations, and interactions of the surface molecules are crucial for many chemical and physical processes that occur at the interfaces. − For example, the surface potentials, surface wettability, the kinetics of the surface reactions, and the surface adsorption energies are all directly influenced by the molecular orientations and packing structures within the interfacial layers. , Hence, a variety of advanced experimental techniques − have been developed to probe the molecular arrangements of the interfaces. Notably, sum frequency generation vibrational spectroscopy (SFG-VS) has been proven to be one of the most powerful spectroscopic tools that can explore the microscopic structures of the liquid surfaces , owing to its submonolayer sensitivity , and intrinsic surface selectivity .…”

In Situ Spectroscopic Probing of Polarity and Molecular Configuration at Aerosol Particle Surfaces

“…Only a few techniques are available for investigating liquid surfaces, − not to mention the surfaces of liquid droplets. Second harmonic generation (SHG) and sum frequency generation (SFG) are two of the proven surface-sensitive methods to investigate liquid surfaces. ,− As a spectroscopic technique, SFG is anticipated to provide vibrational structures, ,− ,− as well as electronic characters, ,− both of which are essential to understanding chemical and physical properties of surfaces. Several groups demonstrated the applications of the SHG and SFG techniques in atmospheric science. ,− These pioneering works have shown cases of the powerful surface-specific techniques.…”

Adsorption and Oxidation Dynamics of Disperse Orange 3 on a Polycrystalline Pt Electrode Studied by In Situ Second Harmonic Generation

“…Simultaneously, a new peak at 361 nm appeared, and the peak intensity gradually increased, which was an indication of the presence of a partial quinoid. , These spectral changes were due to the breakdown of the azo bond and the formation of oxidation product Q, which was also consistent with the results of the CV curve (Figure ). The adsorption peak of oxidation product Q centered at 361 nm and its absorbance intensity were relatively small at the SH wavelength of 404 nm (Figure S3); therefore, the oxidation product absorption is far from the SHG resonance . The SHG resonance at 404 nm is mainly attributed to the DO3 molecules.…”

“…The adsorption peak of oxidation product Q centered at 361 nm and its absorbance intensity were relatively small at the SH wavelength of 404 nm (Figure S3); therefore, the oxidation product absorption is far from the SHG resonance. 66 The SHG resonance at 404 nm is mainly attributed to the DO3 molecules. Although the change in the peak at 427 nm appeared to be negligible in the potential range from −0.05 to 0.6 V, the decrease in the peak intensity could still be distinguished after careful inspection, as shown in Figure 8B.…”