On photokinetics under monochromatic light

Abstract

The properties of photokinetics under monochromatic light have not yet been fully described in the literature. In addition, for the last 120 years or so, explicit, handy model equations that can map out the kinetic behaviour of photoreactions have been lacking. These gaps in the knowledge are addressed in the present paper. Several general features of such photokinetics were investigated, including the effects of initial reactant concentration, the presence of spectator molecules, and radiation intensity. A unique equation, standing for a pseudo-integrated rate law, capable of outlining the kinetic behaviour of any photoreaction is proposed. In addition, a method that solves for quantum yields and absorption coefficients of all species of a given photoreaction is detailed. A metric (the initial velocity) has been adopted, and its reliability for the quantification of several effects was proven by theoretical derivation, Runge–Kutta numerical integration calculations and through the model equation proposed. Overall, this study shows that, under monochromatic light, photoreaction kinetics is well described by Φ-order kinetics, which is embodied by a unifying model equation. This paper is aimed at contributing to rationalising photokinetics via reliable, easy-to-use mathematical tools.

On photokinetics under polychromatic light

“…The phototransformation mechanisms studied in the present contribution are worked out from the -shaped reaction mechanism described in a previous study ( Maafi, 2023 ). Special attention is dedicated to the photomechanisms that operate most of the known organic actinometers ( Kuhn et al, 2004 ; Braslavsky, 2007 ), as shown in Scheme 1 .…”

“…The number of photons entering the reactor ( ) is measured as a sum of the number of photons delivered at each wavelength ( , in ). The detailed derivation of (expressed in ) was previously provided ( Maafi, 2023 ). This number of photons will naturally depend on both the span of wavelength ( ) considered for the measurement and the profile of the lamp ( ) used for irradiation.…”

“…In another perspective, quantification of reactivity by initial reaction-velocity has been performed by using a polynomial probe function to fit the experimental kinetic traces ( Pino-Chamorro et al, 2016 ).The fitting of photoreaction data has also been performed by applying numerical integration methods to the rate law, including the Runge–Kutta ( Chernyshev et al, 2018 ) and Euler methods ( Lente and Espenson, 2004 ; Michnyóczki et al, 2021 ). A discussion of the efficiency of numerical methods specifically for the elucidation of photokinetics showed the limitation of such methods owing to the occurrence of identifiability and/or distinguishability issues ( Maafi, 2023 ). Overall, experimental data were well-fitted by the above individual techniques.…”

Development of a Horizontal Dynamically Mixed Flow Reactor for Laboratory Scale-Up of Photochemical Wohl–Ziegler Bromination

“…In 2005, a landmark publication from Booker-Milburn and Berry (GSK) et al described a photochemical plug flow reactor (PFR) using readily available fluorinated ethylene propylene (FEP) tubing and mercury broad-spectrum lamps and subsequently sparked a renaissance in photochemistry . Coupled with the advent of cheaper monochromatic light sources, i.e., light emitting diodes (LEDs), there has been an explosion in new chemical transformations reported in the literature, from both academia and the pharmaceutical industry. − As these new transformations are implemented into the construction of active pharmaceutical ingredients (APIs), a perennial question arises: how do you scale photochemical transformations? Continuous flow chemistry has received much attention for scaling photochemistry due to the increased surface area to volume ratio which satisfies issues around the penetration of light (Beer–Lambert law) and the intensity of light (Bunsen–Roscoe law). , As intimated above, there are added complexities to reactor design for photochemistry, and both light penetration and the use of heterogeneous catalysis remain unresolved issues when designing reactors. In recent years, different types of reactors have been described in the literature as a solution to performing photochemistry on scale. − These reactors tend to follow a PFR design (Figure a), although the design of immersive modular photoreactors with static mixing has recently been reported to increase mass transfer in the system .…”

“…12 Continuous flow chemistry has received much attention for scaling photochemistry due to the increased surface area to volume ratio which satisfies issues around the penetration of light (Beer−Lambert law) and the intensity of light (Bunsen−Roscoe law). 13,14 As intimated above, there are added complexities to reactor design for photochemistry, and both light penetration and the use of heterogeneous catalysis remain unresolved issues when design-ing reactors. In recent years, different types of reactors have been described in the literature as a solution to performing photochemistry on scale.…”