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Molecular photodynamics can be dramatically affected at the water/air interface. Probing such dynamics is challenging, with product formation often probed indirectly through its interaction with interfacial water molecules using time-resolved and phase-sensitive vibrational sum-frequency generation (SFG). Here, the photoproduct formation of the phenolate anion at the water/air interface is probed directly using time-resolved electronic SFG and compared to transient absorption spectra in bulk water. The mechanisms are broadly similar, but 2 to 4 times faster at the surface. An additional decay is observed at the surface which can be assigned to either diffusion of hydrated electrons from the surface into the bulk or due to increased geminate recombination at the surface. These overall results are in stark contrast to phenol, where dynamics were observed to be 104 times faster and for which the hydrated electron was also a photoproduct. Our attempt to probe phenol showed no electron signal at the interface.

A dual-function student-crafted instrument is described as part of a laboratory activity aimed to teach both the principles and practical aspects of absorption spectroscopy to secondary and introductory undergraduate students. Using minimal changes in an arrangement that is based on interlocking bricks and low-cost components, both a fluorometer and photometer have been constructed. The former demonstrates the principles of the Beer–Lambert law visually and quantitatively by acquiring the spatial light attenuation through a fluorescent sample. The latter then demonstrates its practical application in a visible-light spectrometer by measuring the absorption spectrum of an aqueous permanganate solution.

Excited state dynamics of molecules at interfaces can be studied using second-order non-linear spectroscopic methods such as time-resolved electronic sum-frequency generation (SFG). However, as such measurements inherently generate very small signals, they are often overwhelmed by signals originating from fluorescence. Here, this limitation is overcome by optical Kerr gating of the SFG signal to discriminate against fluorescence. The new approach is demonstrated on the excited state dynamics of malachite green at the water/air interface, in the presence of a highly fluorescent coumarin dye, and on the photo-oxidation of the phenolate anion at the water/air interface. The generality of the use of optical Kerr gating to SFG measurements is discussed.