Electron mobility with photoredox catalysis
Dr Somesh Sharma senior vice president and head of discovery chemistry solutions at Aragen Life Sciences , discusses how photochemistry offers an alternative to conventional processes for functional transformation in organic synthesis
Nature has always inspired scientists over the years . Now , there is a big buzz about sustainability and carbon zero technological platforms to build a safer and healthier environment for future generations . Chemists generally employ conventional processes ( thermal or catalytic activation ) for any kind of functional transformation in organic synthesis . There is an urgent need to make chemical conversions greener , safer and environment-friendly . Photochemistry and especially photocatalysis provide a suitable alternative to traditional approaches : a disruptive and transformative platform learned from nature of harnessing light to thermal energy , for instance , vitamin D and photosynthesis processes . The implementation of any new technology hinges on its versatility , modularity , scalability , safety and sustainability . Early perceptions on photochemistry , however , were to overlook and avoid it because of the intractable challenges of reproducibility , robustness and scalability - an attenuation effect of photon transport . A huge surge has been witnessed in the last few decades ( Figure 1 ), along with increased knowledge of organic and organometallic species , and their distinct properties in converting light to chemical energy for new chemical
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1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021
Figure 1 – Publication counts on photoredox catalysis Note : Scifinder search , 25 December 2021
bond integrations . Generally , a photoredox catalysis ( PC ) process is established , wherein a single electron transfer ( SET ) between the excited state of a photocatalyst and organic substrate gives rise to highly reactive species , yielding unique products .
Selection parameters
To make any photochemical process viable its fundamental concerns – the photon source , the reaction medium and the type of vessel - need to be addressed . UV-induced photochemistry is well reported in the literature via [ 2 + 2 ] cycloadditions and Norrish-type reactions arising from homolytic bond cleavage .
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These forms of radiation have limitations on selectivity and tolerability owing to the high associated energy and broad wavelength range . The deployment of appropriate wavelength filters , such as perfluoroalkoxyalkanes ( PFAs ), perfluoroethylenepropylen ( FEP ), quartz , pyrex and corex , and light sources with a narrow spectral range , is therefore preferred . LED lights have circumvented some of the issues but are plagued with the inherent problem of low intensity and lifetime stability . Efforts are being made to develop high performance LEDs stemming from sapphire technology , so as to produce highly efficient lights with narrow spectral ranges .
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