Reply to Commentary by Trentham et al. on "Caged Phosphate and the Slips and Misses in Determination of Quantum Yields for Ultraviolet-A-Induced Photouncaging" by Gasser et al.

Following a recent communication on the determination of quantum yields for ultraviolet-A-induced photouncaging written by a few of us (P.A. , A.L. , and G.G.), Dr. Trentham contacted ChemPhysChem because he doubted the experimental results presented in that article. In a commentary co-authored with several colleagues, Dr. Trentham has argued in favor of the initial quantum yields determined by Kaplan et al. 37 years ago, that our measurements disproved. The arguments of the commentary are based on several photouncaging studies conducted since the pioneering work of Kaplan et al. However, the commentary by Trentham and his colleagues could not pinpoint the errors that could have led to the markedly different results obtained in our group, apart from suggesting an instrumentation failure. This explanation can be ruled out with a relative certitude, as different instruments were used in our (P.A. , A.L. , and G.G.) initial study to exclude this as possible source of error. Nevertheless, this commentary has sparked our motivation to continue our investigations and to find an explanation for the issues around the determination of uncaging quantum yields. We therefore contacted a colleague with experience in the field of caged compounds, Prof. Christian Bochet (C.B.), and asked him and his coworker Dr. Elia Janett (E.J.) to independently determine the uncaging quantum yield of caged phosphate in his laboratories, using his experimental protocols and equipment, and this without the presence of P.A, A.L. , or G.G. We would like to point out at this stage that both project investigators (C.B. and G.G.) are not related and have not been involved in any common projects to date. In this article, we (P.A. , A.L, E.J. , C.B. , and G.G.) not only present these new results, but also speculate on potential explanations for the divergences in the determined uncaging quantum yields. The new measurements were performed on an Atlas Photonics LUMOS 43 A photoreactor equipped with LEDs with a center-wavelength of 360 nm and using a standard 1 cm absorbance quartz cell. The emission spectrum of these LEDs is quite narrow (bandwidth <10 nm) and thus close to monochromatic. The total photon flux was determined by phenylglyoxylic acid actinometry. Generally, quantum yields are defined as described by Equation (1):