A fiber-optic spectroscopic setup for isomerization quantum yield determination

Abstract

A spectroscopic setup for isomerization quantum yield determination is reported. The setup combines fiber-coupled LEDs, a commercially calibrated thermopile detector for measurement of the photon flux, and a fiber-coupled UV-vis spectrometer. By solving the rate equations numerically, isomerization quantum yields can be obtained from the UV-vis absorption spectra. We show that our results for the prototypical photoswitch azobenzene are in excellent agreement with the literature. The analysis of the errors showed that the quantum yields determined using this method are in the same order of magnitude as when using actinometry, thus demonstrating the reliability of our setup.

Keywords: UV–vis spectroscopy; isomerization; molecular photoswitches; photochemistry; photon flux.

Figure 1

a) Schematic overview of a photochemical isomerization and b) absorption spectra of the isomers of azobenzene.

Figure 2

a) Scheme of the setup and b) picture of the setup.

Figure 3

A visual example of the power determination. a) Power without any elements (left) and with insulated jacket and cuvette (right side, the change in baseline is noticeable), b) power with insulated jacket and cuvette after baseline subtraction.

Figure 4

UV–vis absorption spectra of azobenzene upon irradiation at 340 nm (methanol solution, 20 °C). a) Evolution of spectra over time under irradiation and b) absorption at 340 nm over time, with fitted total absorbance curve obtained from Equation 5. The curve was obtained from entry 5 of Table S2 (Supporting Information File 1).