PHOTOCAT24: The Best of the First Edition

With more than 185 attendees, PHOTOCAT24 has been a real success. The photochemical community is vital and vibrant, as the young researchers that have attending the conference. With the help of light, we can perform unique transformations…and we are sure there will be even more to discover and discuss in the future edition. PHOTOCAT “School of Photochemistry: from Photocatalysis to Photobiology”, a summer school dedicated to the captivating world of photochemistry, was born from the pressing need for an event that would serve as a melting pot for PhD students, postdocs, and young researchers from every corner of the globe. Two years of dedicated effort by the scientific committee (Prof. Luca Dell'Amico, Prof. Shoubhik Das, Prof. René Königs, Prof. Bartholomäus Pieber, Prof. Marcos Suero, and Prof. Olalla Vázquez) and the organizing committee (Sara Cuadros, José Garrido, Giulio Goti, Daniele Mazzarella, and Katy Medrano) culminated in the realization of the inaugural edition of PHOTOCAT in June 2024. The summer school was sponsored and supported by Elsevier, Thieme, European Journal of Organic Chemistry (EurJOC), Chemical Science (ChemSci), Chemical Communications (ChemComm), European Chemical Society (EuChemS), Società Chimica Italiana (SCI), Institute of Science and Technology Austria (ISTA), Real Sociedad Española de Química (RSEQ), Gesellschaft Deutscher Chemiker (GDCh), and Gesellschaft Österreichischer Chemiker (GöCH). “It took about two years to organize the event; we started selecting the speakers and the venue and arranging the time in such a way that the participants, as well as the speakers, would have time to discuss science but also to live the city and its beauty. Time to think on new photochemical reactivity and time to refresh their minds with art and culture… Food and wines are also part of our cultural background, and we decided also to take very care on these aspects”, Prof. Luca Dell'Amico said. The event took place in Padova, renowned as the home of one of the world's oldest universities (founded in 1222), which served as the perfect venue. Prof. Luca Dell'Amico welcomed all the guests and shared general information about this developing project. The school featured the participation of 16 plenary speakers and 10 oral communications from selected researchers and professors (Davide Audisio, Joshua-Philip Barham, Guillaume Dagousset, Sara Filgueira, Dana Králová, Manuel Plaza, Yuman Qin, Anna F. Tiefel, Songwei Wen, and Juntao Ye). In this first edition, 185 participants from more than 20 countries representing five continents attended the school. Following a compelling introduction by the chair of PHOTOCAT24, Prof. Luca Dell'Amico, Prof. Erick Carreira captivated the audience with his inaugural lecture on Sunday, June 2nd. He began by summarizing the remarkable work achieved by his group in the functionalization of olefins, emphasizing their groundbreaking contributions to cobalt-based catalysis.1 Building on these essential contributions, he highlighted the latest developments that leverage photocatalytic tools within Co-catalyzed protocols. Notably, this innovative strategy has been successfully applied to a photo-semipinacol rearrangement utilizing unactivated allylic alcohols, as well as to the synthesis of heterocycles through the cycloisomerization of olefins.2, 3 These advancements not only showcase the potential of cobalt-based methods but also pave the way for future breakthroughs in synthetic chemistry. Up next, Prof. Burkhard König delivered an engaging presentation titled “Better Organic Synthesis with Light,” showcasing his groundbreaking research in photocatalysis at the oil-water interface. He emphasized how this innovative approach streamlines coupling reactions in water, effectively utilizing substrates with varying electron affinities.4 Prof. König then revealed compelling findings regarding the formation of diverse carbanion intermediates, highlighting superbasic anions generated through a reductive radical-polar crossover (RRPCO) process and the remarkable α-amino carbanion type.5 Notably, these highly reactive intermediates possess the capability to deprotonate common polar solvents like acetonitrile, dimethyl sulfoxide, and N,N-dimethylformamide, thus opening new avenues for novel organic transformations. The second day started with a talk by Prof. Daniele Leonori. He shared some of his most significant discoveries, such as the use of amine-borane reagents for the generation of reactive boryl radicals. These intermediates possess a unique reactivity that enables borylation reactions with unusual selectivities and their use as halogen-atom transfer reagents.6 Then, he introduced to the audience the innovative use of nitroarenes as photo-responsive ozone surrogates that can undergo [3+2] cycloaddition with alkenes.7 This approach enables the selective conversion of double bonds into carbonyl compounds even when several reactive sites are present in the substrates. Steric and polar effects play a key role in driving the selectivity of this oxidative cleavage. The next speaker was Prof. Ryan Gilmour, who began his talk by discussing his research focused on discovering new strategies to enable alkene isomerization mediated by energy transfer processes. He showed the isomerization of alkenyl boronates by energy transfer in the presence of thioxanthone photosensitizer as a convenient strategy to access bioactive polyenes.8 Finally, he discussed the photochemical deracemization of cyclopropanes enabled by an Al-salen catalyst that acts both as a photocatalyst and grants a chiral environment for a deracemization process.9 After lunch, it was Prof. Corinna Schindler's turn. She enlightened the audience with a discussion on the chemistry of azetidines and their synthesis through photocycloadditions. The presentation was an exciting journey through her discoveries in the aza Paterno-Büchi reaction using unexplored imine substrates, which facilitate the control and modulation of reactivity. In the first part, Prof. Schindler discussed her pioneering research from 2019, in which she reported the synthesis of azetidines using oximes and alkene moieties.10 The conversion of symmetric 2,3,4-trisubstituted azetidines into specific N-substituted nitro derivatives that can be used as an alternative to trinitrotoluene arose from a thought-provoking discussion.11 Prof. Dorota Gryko delivered the final talk of the day, focusing on her research in developing sustainable synthetic methods using vitamin B12 as a photocatalyst. She explained how a cobalester derivative, synthesized by her group in 2014, improved the reactivity and solubility properties of vitamin B12.12 Specifically, she discussed the novel compound's photocatalytic activity in the homocoupling reaction of benzyl bromide. During her presentation, Prof. Gryko highlighted the powerful combination of using B12 as a Co catalyst with Ni catalysis for the opening reaction of epoxides with aryl halides.13 On the third day, Prof. Rentmeister gave a talk titled “Harnessing light to activate mRNA translation”. She discussed how her research group used the RosettaMatch application to regulate a light-dependent 5′ cap guanine-N7 methyltransferase.14 They designed, synthesized, and characterized four variants and demonstrated the importance of using informatics tools in cooperation with experimental characterization to create novel light-dependent enzymes. She introduced a new technique that utilizes 5′ cap analogues called FlashCaps, which contain a photo-cleavable group.15 Under specific irradiation conditions, these FlashCaps can release native mRNA without affecting cell viability and the translation process. Prof. Andrey Klymchenko delivered an engaging presentation on the potential of fluorescence molecular probes and their applications in sensing and imaging biomembranes.16 The talk provided an exciting perspective on the relationship between chemistry and biology and the powerful applications in cell biology. Specifically, Prof. Klymchenko highlighted his research on the design of novel cyanine-based dyes with a low-affinity membrane anchor. This moiety was essential to achieve efficient plasma membrane labelling. Moreover, this cell “barcoding” can be achieved in different colour codes with the variation of the ratio of these dyes.17 Before the lunch break, Prof. Gasser took us on a scientific journey through the synthesis of his new compounds used in photodynamic therapy. His research group has made significant contributions to the development of innovative metal-based photosensitizers that can be used to target various cancer cell lines. Under the slogan “Can we do it better?” Prof. Gasser demonstrated the progression from his initial reports on synthesizing and studying Ru(II)-based compounds to the latest Os(II)-based derivatives.18, 19 He emphasized the importance of deliberate design and structural changes in achieving exceptional performance in photodynamic therapy. After lunch, the discussion continued to explore the integration of photochemistry with modern technologies. Prof. Timothy Noël demonstrated the effectiveness and potential of combining photoredox catalysis with flow chemistry, especially in the field of hydrogen atom transfer (HAT).20, 21 Furthermore, he discussed how to automate chemistry using a robotic platform called RoboChem, which enables the optimization and scaling up of various photoreactions, such as C(sp2)−C(sp3) cross-electrophile coupling and trifluoromethylation reactions.22 In addition, Prof. Noël shared a recent discovery with the audience: his plan to develop 3D-printed photoreactors.23 This initiative aims to make this technology more accessible and easier to use. These cost-effective reactors are designed to achieve multiple objectives, including enhancing energy-efficient batch processes, facilitating the transition from batch to flow, and enabling high reproducibility. Prof. Oliver Wenger presented his latest findings on studying the patterns governing the cage escape factor of radical species. The study focused on two specific metal-based complexes: Ru(II) and Cr(III) photocatalysts.24 The research revealed a correlation between the cage escape quantum yields and the reaction yield when using aliphatic and aromatic amine donors of varying sizes and halogen atoms. The closing of his presentation highlighted the chemistry of excited state of radical anions and their performance as super reductants.25 The significance of the pre-association pathway between these radical species and the substrates was emphasized as a crucial factor in controlling the photoreactivity. Prof. Kirsten Zeitler delivered the final presentation of the day. In the first part of her talk, she exposed her innovative ideas regarding the rational design of IPN-based photocatalysts. Her work involved analyzing the redox potentials resulting from changes in the size and electronic properties of donor moieties and the weakening of acceptor strength.26 Additionally, she discussed her research on NHC catalysis, its application in crossed-acyloin reactions, and the use of resulting products in synthesizing ketones through the photoreduction of the C−O bond.27, 28 This presentation provided an exceptional demonstration of the application of metal-based and organic photocatalysts for the audience. The fifth day started with the talk of Prof. Paolo Melchiorre, who presented his work on the photoactivity of organocatalytic intermediates. He showed how enamines and iminium ions can be implemented in different photochemical strategies such as electron donor-acceptor complex formation, direct photoexcitation, or merger with photocatalysis, enabling novel catalytic functions in the asymmetric domain.29 Subsequently, he described some novel results about the translation of this reactivity under biocatalytic conditions.30 Finally, he discussed the development of a metal-free radical reductive cross-coupling enabled by photoredox and HAT catalysis.31 Prof. Cristina Nevado led the second talk of the day and shared her work on the development of new chemical transformations employing the Truce-Smiles rearrangement. The first results that were disseminated involved one of the most recent studies carried out by Nevado's group on the utilization of chiral arylsulfinylamides to obtain optically pure pharmaceutical motifs. In this exciting modification, the sulfonyl-based chiral auxiliary is not present in the final structure, whereas steric factors dictate the final product's diastereoselectivity.32 Then, we learned more about this type of rearrangement: the sulfinyl-smiles variant. In this research, Prof. Nevado discovered how to achieve asymmetric and remote C(sp3)−H arylation.33 This novel transformation occurs through a HAT pathway and stereocontrolled aryl migration. Prof. Ritter led an inspiring talk on the development of novel chemical reactions. It revealed how we can do safer chemistry by controlling the production of aryl diazonium compounds utilizing thiosulfate or dihalocuprates.34 Even if the main reactivity of this chemical transformation does not involve the use of photocatalysis, it highlights the importance of reinventing old methodologies by employing new technologies and procedures that can replace hazardous reagents. Then, we learned about C−H functionalization via thianthrenation through a persistent radical.35 Interestingly, the thianthrenium salts obtained can achieve different modifications by polar or photoredox processes. This is an essential example of using key intermediates in versatile chemical transformations. Prof. Davide Bonifazi gave the final presentation of this day. He shared his research on the rational design of polycyclic aromatic hydrocarbons (PAH).36 In this theoretical and experimental study, the Bonifazi group demonstrated how to control the optical gap in the PAH due to heteroatom doping patterns. For this purpose, they synthesized and analyzed the oxygen-based analogue of anthanthrene, and also, in this type of molecule, they replaced different C−C bonds with C−N, C−S,37 C−Se bonds. Their findings revealed that these molecules exhibited an interesting behavior. For example, they observed a bathochromic effect when the nitrogen atom was placed in electron-rich positions of the anthanthrene-type core. Additionally, the presence of nitrogen was observed to affect the redox properties of the solid state. On the last day, the PHOTOCAT24 activities changed venue to the “Aula Nasini” at the Department of Chemical Sciences of the University of Padova. This emblematic place was built in 1912, in honor of the Italian chemist Rafaello Nasini, whose findings were significant in applied chemistry research. Here, we enjoyed two talks from our sponsors, Elsevier and Nature Chem. In the first one, Dr. Giulia Moncelsi talked about the impressive research tools provided by the Reaxys platform and how we can potentiate the design of new substances considering its largest physicochemical, toxicology, and bioactivity data as well as the retrosynthetic options supported by artificial intelligence. In the second talk of the day, Dr. Katherine Geogheghan explained the details that one must consider when publishing in Nature journals, specifically in Nature Chemistry. Dr. Geogheghan described the most critical aspects of the writing, submission, editorial, and publication processes. The essential topics of these two final talks are given to the participant's knowledge about two crucial steps in the research: i) the search for new chemical reactivities, and ii) how these discoveries can be shared with the scientific community and broad general audience. Finally, as a closing ceremony, the prizes for the best poster presentation were presented and supported by SYNFACTS, EurJOC, ChemComm, and ChemSci. We were happy to see that the award winners came from universities around the world: Álvaro Maqueda (University of Oviedo, Spain), Alberto Luridiana (University of Cagliari, Italy), Laura Kqiki (Institute of Chemical Research of Catalonia, Spain), Catia Nicoletti (University of Padova, Italy), Sara Sparascio (University of Parma, Italy), Daniel Bím (Institute of Organic Chemistry and Biochemistry of the CAS, Czech Republic). At the end of these six days, the exciting talks from our fantastic speakers inspired the audience to continue searching for new horizons in photochemical reactivity. PHOTOCAT24 closed with some words by Prof. Luca Dell'Amico, highlighting the attendees’ extraordinary participation (Figure 1) and the organizing committee's hard work (Figure 2). Group picture of some of the PHOTOCAT24’s speakers and organisers. Part of the organizing committee and staff of PHOTOCAT24. During the summer school, participants immersed themselves in an inspiring atmosphere filled with innovative discoveries, ranging from photocatalysis to photobiology. The true highlight of this event was the dynamic scientific exchanges among speakers, students, and postdoctoral researchers during both the oral and poster sessions. The inaugural edition of PHOTOCAT “School of Photochemistry: from Photocatalysis to Photobiology” concluded with high hopes for the next event, scheduled to take place in two years in a (at the moment) secret location. PHOTOCAT26 promises to recreate this vibrant environment for the passionate chemical community to showcase their latest advancements in photochemistry. The future of photochemistry certainly holds many surprises and exciting opportunities for expanding our knowledge in this domain. As the organizing committee, we would like to express our gratitude to our sponsors, the University of Padova, all the national chemical societies (a special mention for SCI – Società Chimica Italiana) and the EuChemS, for their support and commitment in making the first edition a great success. We are sure that the next organizers will make the following edition an extraordinary event, and we are confident that the PHOTOCAT project will strengthen over the years, contributing to shaping the next generations of chemists…who like to play and work with light! The authors are extremely grateful to the sponsors especially to Elsevier SYNFACTS, EurJOC, ChemComm, and ChemSci for the best poster presentation prizes. L.D. acknowledges financial support by the University of Padova for the organization of this event. The financial support of the authors is provided by Ministero dell'Università Ministero dell'Università (MUR, C93C22007660006, K.M.U., C93C22007640006, G.G.), Fondazione Cariparo (Starting Package C93C22008360007, K.M.U.), Marie Skłodowska-Curie Actions (SupraPhoCat, project number: 101108382, J.J.G.G.), European Research Council (ERC-Starting Grant 2021 SYNPHOCAT 101040025, S.C., D.M., L.D.). The authors declare no conflict of interest.