Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• their use in applications based on sensitized photoinduced electron transfer. This can be NIR-sensitized photopolymerization resulting in formation of initiating radicals and conjugate acid [5][6][13][14][15][63][64]. Recently, the use of NIR-LEDs exhibiting high excitation intensity brought more light

• in this field and helped to understand the function of existing intrinsic barrier in such systems comprising cationic cyanines in photoinduced electron transfer systems [65]. Furthermore, the huge amount of heat released by nonradiative deactivation of the excited state brings up to use them as

• emission between 800–1100 nm. Such findings enforce activities to make absorbers exhibiting internal barriers in photoinduced electron transfer reactions [72] resulting in a certain white light stability under ambient light conditions. Such properties can be seen as a big benefit from a practical point of

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• electron-transfer reaction, while ion binding blocks this quenching pathway restoring emission. Thus, ion liberation from 1 and transfer to 3 would result in a fluorescence off–on switching of the latter. To perform the ion-transfer experiment, the fluorescent dye is loaded with one equivalent of Ca2

• liberation of Ca2+ upon photexcitation in solution, azobenzene macrocyle 1 was used as a reversible Ca2+ photoejector in the presence of a Ca2+-selective “turn-on” fluorescent probe (3, Figure 7) [41]. The fluorescence of BODIPY dye 3 in the absence of calcium, is quenched by an intramolecular photoinduced

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• electron-transfer phenomena or two-photon absorption [32][33][34][35][36]. As part of our research program we have developed arylisoquinolines that integrate a boronic acid ester [37][38][39] or a BMes2 unit [6][40]. The presence of the boron-substituent confers interesting photophysical properties to

• , boron with sp2 hybridization, such as in triarylboranes, offers the possibility to modulate fluorescence properties by the addition of Lewis bases (e.g., fluoride ions [27][28][29][30][31]) or by exploring the electron-accepting properties of the boron, including charge-transfer and photoinduced

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• . Thus, these complexes could be useful for designing functional molecular crystals and materials which can be applied for the study of photoinduced electron transfer and energy conversion towards application in the field of molecular electronics. 3. Molecular reactors Designing synthetic host systems

• ·TCNQ]2+ complex by pre-reduction to a [TCNQ]−· anion radical in situ, and encapsulation in the host, photochemical excitation of the porphyrin unit in the reactor, photoinduced electron transfer from the excited porphyrin unit to a neutral TCNQ, giving rise to a porphyrin radical cation and a second

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• potential of dyes, rendering the photoinduced electron-transfer reaction with guanine residues in DNA energetically disfavored and resulting in higher fluorescence quantum yields. However, in the absence of redox potential data, this assumption could not be experimentally verified. Finally, we showed that

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8][28][29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• photoinduced electron transfer processes. A major theme of research that has emerged from these studies is the application of various cocatalysts to intercept the organoradical intermediates of photoredox reactions and modulate their subsequent reactivity [5][6]. The combination of photoredox catalysis with

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• (without considering the solvent term) [29] we estimated the excited state potential of these catalysts to be as low as Ered(X+·/X*) ≈ −2.9 to −3.0 V (vs SCE). The proposed photoredox catalytic mechanism (Figure 4) for the nucleophilic addition of methanol to olefins starts with photoinduced electron

• transfer from the N-phenylphenothiazine (1) as photocatalyst to 13a as substrate. The resulting substrate radical anion 13a−· is instantaneously protonated to radical 13a· and back-electron transfer to the intermediate phenothiazine radical cation 1+· yields the substrate cation 13a+. The latter is

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• and redox reactions are possible. This process is called photoinduced electron transfer (PET). In this context, photoredox catalysis was developed. Light is used to excite the photoredox catalyst which allows electron transfer processes with additives. Both oxidation and reduction reactions can be

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• excited state (S1) or a triplet excited state (T1), by absorption of a photon with energy hν, which then undergoes photoinduced electron transfer (PET). Following this, the photocatalyst is reduced or oxidised accordingly, such that it returns to its ground state and native oxidation state (Figure 1 and

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a

• quenching by photoinduced electron transfer (PET), whereas the protonated form was brightly fluorescent [31]. We report herein the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we

• . This includes indicator displacement assays with favourable absorption and emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization with fluorophores. Keywords: BODIPY; cucurbituril; fluorescence; pH; photoinduced electron

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• 2b and 2c are very low (Φfl < 0.02). Such low emission intensities have been observed also for donor-substituted 9-arylbenzo[b]quinolizinium derivatives and explained either with a radiationless deactivation of the excited state by torsional relaxation or by a photoinduced electron transfer [33][49

• titration. The fluorescence intensity of the derivatives 2a and 2d is significantly quenched by the addition of DNA, respectively (Figure 8 and Figure 9). This observation usually indicates a photoinduced electron transfer between the excited molecules and the DNA bases [69]. By contrast, the association of

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• DNA or the tryptophan (Trp) amino acid residue through a photoinduced electron-transfer (PET) process [16][17][18][19]. Interestingly, the two radical species generated by this PET can recombine to form a covalent photoadduct [20][21][22]. When this photoadduct is formed with the guanine base, the

• ). This quenching of the luminescence of conjugate 9 in the presence of GMP reveals that a photoinduced electron transfer can take place between the excited complex and the guanine moiety, which could give rise to the formation of a photoadduct from the recombination of the monoreduced complex and the

• radical guanine generated after the photoinduced electron transfer (PET). In order to confirm the occurrence of PET, transient absorption measurements with conjugate 9 were performed in the absence and in the presence of GMP. The recorded transient absorption spectra are presented in Figure 5. In absence

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• conjugation. The electronic interaction between the covalently connected chromophore unit leads to important changes in the absorption spectra and so these dimers are expected to serve as attractive building blocks for the construction of multicomponent photoinduced electron transfer supramolecular systems

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

• Stephen Hill and
• M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

• tested, in the case of Cu2+, a significant reduction in fluorescence was recorded. The authors proposed that Cu2+, due to its paramagnetic nature, could quench the S-CD fluorescence via a photoinduced electron transfer mechanism, in which Cu2+ is reduced to Cu+. The presence of Cu+ was confirmed by

Synthesis and fluorosolvatochromism of 3-arylnaphtho[1,2-b]quinolizinium derivatives

• Phil M. Pithan,
• David Decker,
• Manlio Sutero Sardo,
• Giampietro Viola and
• Heiko Ihmels

Beilstein J. Org. Chem. 2016, 12, 854–862, doi:10.3762/bjoc.12.84

• substituent (tolyl < naphthyl ≈ phenanthryl). Such a red shift of the emission bands was already observed for acridinium- and benzo[b]quinolizinium-containing biaryl derivatives and shown to result from a photoinduced electron transfer from the electron-donating aryl unit to the excited cationic hetarene

Self and directed assembly: people and molecules

• Tony D. James

Beilstein J. Org. Chem. 2016, 12, 391–405, doi:10.3762/bjoc.12.42

• templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling

• fluorescent photoinduced electron transfer (PET) pH sensors developed by A. P. De Silva (Figure 3) [17] in order to develop a fluorescence sensor for saccharides [18]. Thus creating a system where the neighbouring nitrogen lowered the working pH of the boronic acid and provided a fluorescence signalling

• Shinkai, Director of the ERATO Chemirecognics Project (1990–95) [13]. Fluorescence photoinduced electron transfer (PET) pH sensor developed by A. P. De Silva. Fluorescence PET sensor for saccharides. (a) Glucose selective PET system. (b) Chiral discriminating PET system. (a) Fluorescence photoinduced

Art, auto-mechanics, and supramolecular chemistry. A merging of hobbies and career

• Eric V. Anslyn

Beilstein J. Org. Chem. 2016, 12, 362–376, doi:10.3762/bjoc.12.40

• soda indeed sparked the idea of pursuing a citrate sensor, the idea of working on sensing had been percolating in my mind for a while. A. P. De Silva was pioneering the use of PET (photoinduced electron transfer) signaling [71], Seiji Shinkai (and his post-doctoral associate Tony James) were creating

Bright molecules for sensing, computing and imaging: a tale of two once-troubled cities

• A. Prasanna de Silva

Beilstein J. Org. Chem. 2015, 11, 2774–2784, doi:10.3762/bjoc.11.298

• identification, nanometric mapping, animal visual perception and visual art are also outlined. Keywords: blood electrolyte analyzer; luminescent PET sensing/switching; molecular logic-based computation; photoinduced electron transfer; small molecular edge detection; Review Prologue Colombo, Sri Lanka: A civil

• from this ferment was photoinduced electron transfer (PET) [6][7], especially following the previous realization of its central role in green plant photosynthesis. It appealed to the physicochemical side of me that PET allows one to think primarily in terms of redox potentials, while atomic details

• electron transfer) sensing/switching as a design tool, b) the construction of a market-leading blood electrolyte analyzer and c) the invention of molecular logic-based computation as an experimental field, are delineated. Efforts to extend the philosophy of these approaches into issues of small object

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

• Baiba Turovska,
• Henning Lund,
• Viesturs Lūsis,
• Anna Lielpētere,
• Edvards Liepiņš,
• Sergejs Beljakovs,
• Inguna Goba and
• Jānis Stradiņš

Beilstein J. Org. Chem. 2015, 11, 2166–2170, doi:10.3762/bjoc.11.234

• , Langelandsgade 140, DK 8000 Aarhus, Denmark 10.3762/bjoc.11.234 Abstract Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by 3O2 if the solution is exposed to sunlight. The driving force for the photoinduced electron transfer is calculated

• ; photoinduced electron transfer; pyrrolidine; tetrahydropyridine; Introduction Increased attention has been paid to the chemistry of cyclic organic peroxides since it was found that naturally occurring representatives of this group possess biological activity, particular antimalarial [1][2]. Significantly less

• anion of O2 (O2−•) is spin permitted [19], however, it is not thermodynamically favourable. The driving force for the photoinduced electron transfer can be calculated from electrochemical and spectroscopic measurements made in the same solvent according to Weller’s approximation [20] where is the

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

• Redouane Beniazza,
• Natalia Bayo,
• Florian Molton,
• Carole Duboc,
• Stéphane Massip,
• Nathan McClenaghan,
• Dominique Lastécouères and
• Jean-Marc Vincent

Beilstein J. Org. Chem. 2015, 11, 1950–1959, doi:10.3762/bjoc.11.211

• efficient photoinduced electron transfer process leading to a fast Cu(II) to Cu(I) reduction, the final electron source being the solvent. The photoreduction process was extremely efficient, photoreduction quantum yields (Фred) ranging from 0.17 up to around 1 being measured in good H-atom donating solvents

Synthesis and spectroscopic properties of β-triazoloporphyrin–xanthone dyads

• Dileep Kumar Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2015, 11, 1434–1440, doi:10.3762/bjoc.11.155

• synthesized and evaluated for their photophysical properties. These compounds have successfully demonstrated the occurrence of an excited electron transfer from the porphyrin subunit to the attached acceptor moieties. On the other hand, some photoinduced electron transfer systems such as porphyrin

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

• Diego Cortizo-Lacalle,
• Calvyn T. Howells,
• Upendra K. Pandey,
• Joseph Cameron,
• Neil J. Findlay,
• Anto Regis Inigo,
• Tell Tuttle,
• Peter J. Skabara and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2683–2695, doi:10.3762/bjoc.10.283

• the triads, theoretical DFT and TDDFT calculations were performed. Keywords: BODIPY; diketopyrrolopyrrole; organic semiconductors; organic solar cells; thiophene; Introduction The discovery of photoinduced electron transfer from conjugated polymers to fullerene (C60), and the favourable

An integrated photocatalytic/enzymatic system for the reduction of CO₂ to methanol in bioglycerol–water

• Michele Aresta,
• Angela Dibenedetto,
• Tomasz Baran,
• Antonella Angelini,
• Przemysław Łabuz and
• Wojciech Macyk

Beilstein J. Org. Chem. 2014, 10, 2556–2565, doi:10.3762/bjoc.10.267

• generates a photocurrent upon visible light irradiation, proving a photoinduced electron transfer from the excited chromium(III) complex to the conduction band of TiO2 (Figure 6). The following step, that is, the transfer of electrons from the conduction band of the photocatalyst to the oxidized form of the

• photoinduced electron transfer from Cr(III) to the conduction band of TiO2 and further to the adsorbed rhodium complex. A hindered back electron transfer from the Rh species to the photocatalyst can also be responsible for the overall efficiency of the process. Substitution of Rh with Ir and of bipyridine with

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• ; photocatalysis; photoredox catalysis; redox; semiconductor; Introduction Stimulated by the principles of sustainable chemical synthesis and the progress in our understanding of catalytic and photoinduced electron-transfer processes, in recent years photoredox catalysis emerged as a new and powerful area for