Solar Photochemistry in Flow

Abstract

In recent years, photochemistry has been a highly active research field. This renaissance is linked to the upsurge of photoredox catalysis, a versatile platform for synthetic methodologies using visible light photons as a traceless reagent. In contrast with UV, visible light constitutes almost half of the ground solar irradiance, making the use of solar light in chemistry a sustainable and viable possibility. However, the direct use of sunlight to power chemical reactions is still little explored. This can be explained by both the hurdles associated with solar radiation (e.g., its variability, irreproducibility, high IR content, etc.) and the need for a specialized photoreactor. Most of these issues can be tackled with technological solutions, and especially with the recourse to flow chemistry. Flow chemistry goes hand in hand with photochemistry thanks to the uniform irradiation it provides to the reaction. Furthermore, a continuous-flow reactor can be easily integrated with different solar collectors (including compound parabolic concentrators and luminescent solar concentrators) and constitutes the most efficient approach to solar photochemistry. After a description of the characteristics of the solar radiation relevant to chemistry, this chapter critically describes the different type of solar photoreactors and their applications in synthetic organic chemistry. Finally, an outlook on the future of solar photochemistry in flow is included.

Flow Photochemistry: Shine Some Light on Those Tubes!

“…As it contains UV, visible, and IR light, sunlight is theoretically a suitable light source for a variety of transformations. The rediscovery of sunlight has recently led to diverse research investigations and many photochemical transformations have been performed under the sun [54][55][56]. However, the polychromatic nature of sunlight is also a downside, as it may result in nonselective transformations.…”

Continuous Flow Photochemistry for the Preparation of Bioactive Molecules

“…Noël and co-workers [43,44] have recently described the exploitation of solar light in continuous flow settings. The use of solar light is highly attractive [45]-and in fact the first photochemical transformations were studied using sunlight [46,47] (many of which are associated with the pioneering works of Cannizzaro, Paterno and Ciamician); however, the heterogeneity of solar light (≈5% UV, ≈43% visible, ≈52% IR), together with inconsistent photon flux (seasons, cloud coverage, day/night pattern and geographical impact), make this approach challenging.…”

Flow Chemistry in Contemporary Chemical Sciences: A Real Variety of Its Applications

“…Furthermore, there were also reviews on the spectroanalytical applications of multi-syringe flow-injection methods [355], as well as on the application of fluidized particles in flow analysis methods [356], microfluidic paper-based analytical devices [262], or the use of flow analysis for the determination of radionuclides in nuclear industry [357]. Among the recent reviews on the technological applications of flow methods, much attention was focused on photochemical methods [85] and solar photochemistry [224].…”

“…Photochemical reactions were given increasing attention in recent years in the area of developing continuous-flow synthetic systems, as well illustrated by several reviews [85,154,211]. This also includes solar photoreactors [224]. The main advantages of using continuous-flow photochemistry in organic synthesis are as follows: short process time, high selectivity, the possi-bility of handling hazardous intermediates in a safe way, and straightforward scaling-up [85].…”