Usefulness of Φ-order kinetics for the investigation, characterisation and quantification of photodegradation processes

Abstract

AbstractΦ-order kinetics has been shown to be the best tool to study photokinetics [1 -6]. Various species have been studied using this approach including photochromes [1,2] and drugs [3 -6]. The unimolecular photodegradation processes of the form AB (1Φ) and photoreversible systems AB (2Φ), where A, the initial species phototransforms into a product B (A→B) which itself can return to A (A→B) via two dis nct photoprocesses, each characterized each by an individual efficiency (Φ), have been mathematically described by integrated rate-law equations which express the so called 'Φ-order' kinetics [1 -6]. The application of this novel approach was found to be useful to determine a number of photoreaction attributes. The reaction's photochemical quantum yield(s), the effects of initial species concentration, or the impact of competitive absorbers on the rate-constant of the photoactive species were all made readily accessible by simple methods. More importantly, the Φ-order kinetics has proven to facilitate the development of a wide range of actinometers from AB (1Φ) and AB (2Φ) systems [2 -6]. This novel Φ-order kinetic method clearly has the potential for application in various fields including the photodegradation of natural products. The details of Φ-order elucidation kinetic methods will be discussed here and examples of application presented.