Photo, thermal and chemical degradation of riboflavin

• Muhammad Ali Sheraz,
• Sadia Hafeez Kazi,
• Sofia Ahmed,
• Zubair Anwar and
• Iqbal Ahmad

Beilstein J. Org. Chem. 2014, 10, 1999–2012, doi:10.3762/bjoc.10.208

• photodegraded to LC whereas in alkaline media it forms LC along with LF. Both these major photoproducts are formed via the triplet excited state through the mediation of FMF, which serves as an intermediate in the photolysis of RF [10][11][18][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][59][78

Synthesis of new, highly luminescent bis(2,2’-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole

• Anastasia S. Kostyuchenko,
• Vyacheslav L.Yurpalov,
• Aleksandra Kurowska,
• Wojciech Domagala,
• Adam Pron and
• Alexander S. Fisyuk

Beilstein J. Org. Chem. 2014, 10, 1596–1602, doi:10.3762/bjoc.10.165

• (Figure 1). This fine structure appears to be a manifestation of enhanced vibronic coupling, which clearly suggests rigidification of the excited state molecular geometry of the compounds. This can be anticipated, considering the quinoid bond configuration of the excited state populated LUMO energy level

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

• Nathan J. Gesmundo and
• David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

• irradiation in the presence of oxygen, bicyclic endoperoxides were obtained [12]. Formation of the 1,2-dioxanes was presumed to occur via single electron oxidation of the diene by the excited state DCA followed by either 6-endo or 7-endo cyclization modes to generate a fleeting distonic cation radical species

• triarylpyrylium salts, as they have excited state reduction potentials in excess of +1.7 V vs SCE (Scheme 2) [20]. In addition, prior work demonstrates that these catalysts are productive in cation radical mediated [4 + 2], [2 + 2], oxygenation, and rearrangement chemistry [21][22]. We also sought to delineate

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

• semiconductor particles that absorb in the UV-A and near visible reagion. The widely used TiO2 has found numerous applications in photochemical water detoxification or surface purification because of its favourable excited-state redox properties [11]. In synthetic applications of semiconductor photocatalysis

• titanium species, photolysis at 254 and 300 nm, respectively, led only to trace amounts of the hydroxymethylation product 4 via a (triplet carbonyl) excited-state hydrogen-transfer process, obviously a sluggish process under these conditions (Table 1). In the presence of titanium complexes TiCln(OiPr)4−n

• conditions for route I are fulfilled for TiCl2(OR)2, a species that is capable of oxidizing methanol in the excited state and simultaneously acting as a ground-state Lewis acid that complexes the carbonyl compound. A much weaker Lewis acid such as Ti(OR)4 is capable of methanol oxidation but prefers hydrogen

The Ugi four-component reaction as a concise modular synthetic tool for photo-induced electron transfer donor-anthraquinone dyads

• Sarah Bay,
• Gamall Makhloufi,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 1006–1016, doi:10.3762/bjoc.10.100

• . These novel donor–acceptor dyads are electronically decoupled in the electronic ground state according to UV–vis spectroscopy and cyclic voltammetry. However, in the excited state the inherent donor luminescence is efficiently quenched. Previously performed femtosecond spectroscopic measurements account

• –anthraquinone dyads 8 the donor and anthraquinone moieties are electronically decoupled in the electronic ground state. Fluorescence is an excited-state phenomenon and, therefore, steady-state emission spectra of the donor-only reference systems 2 (Figure 7) and 10 and the donor–anthraquinone dyads 8 were

• nonradiative depopulation of the excited state can be assumed by an electron transfer. This rationale is additionally supported by our previous transient absorption spectroscopic study of the dyad 1 [56]. According to the Weller approximation [87] the driving force for a photo-induced electron transfer leading

Visible light mediated intermolecular [3 + 2] annulation of cyclopropylanilines with alkynes

• Theresa H. Nguyen,
• Soumitra Maity and
• Nan Zheng

Beilstein J. Org. Chem. 2014, 10, 975–980, doi:10.3762/bjoc.10.96

• compounds [21][22][23][24][25][26]. Amines have been used as an electron donor to reduce the excited state of photocatalysts, while they are oxidized to amine radical cations. Our group and others have taken advantage of this facile redox process and developed a number of synthetic methods that harness the

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• a dye (PS) with an electron acceptor (A) is depicted. After absorption of actinic light (hν), the PS reaches its singlet excited state (1PS*) and after intersystem crossing (kISC), its triplet excited state (3PS*). From both these excited states, an electron transfer can occur from the PS to A (with

• possible. The values of the Gibbs free energy change for photoinduced electron transfer is given by the Rehm–Weller equation [56]: , where E* stands for the energy of the excited state. The Coulombic term C is usually neglected in polar solvent. will determine the rate of electron transfer and the dye

• rate constants of singlet and triplet state deactivation to the ground state, respectively; kISC the rate constant of the intersystem crossing from 1PS to 3PS; 1kq/A, 3kq/A, (1kq/D, 3kq/D) the bimolecular electron transfer rate constant of the singlet and triplet excited state of the PS by the acceptor

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• proposed by us in the photopolymerization reactions are depicted in Figure 1 and Figure 2 (for metal based PICs and metal free PICs, respectively) [45][46][47][48][49][50][51][52][53][54][55]. Their reactivity parameters (redox potentials, excited state lifetimes) are given in the associated references

• the encountered mechanisms in various PIC based photoinitiating systems, iv) highlight some examples of high performance PISs and v) present the efficiency of a novel PIC in photopolymerization reactions as well as the excited state processes involved in the photoinitiating systems used. Experimental

Rapid pseudo five-component synthesis of intensively blue luminescent 2,5-di(hetero)arylfurans via a Sonogashira–Glaser cyclization sequence

• Fabian Klukas,
• Alexander Grunwald,
• Franziska Menschel and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 672–679, doi:10.3762/bjoc.10.60

• excited state caused by significant distortion of the aryl substituents from coplanarity in the ground state [42]. Therefore, the geometries of the ground state structures of the compounds 2a,2b,2i,2j, and 2n were optimized on the DFT level of theory (B3LYP functional [43][44][45][46] and the Pople 6-311G

• quantum yield Φf. The same holds true for the comparison of the constitutional isomers 2i and 2j. Therefore, the twisted structure of 2j causes a larger Stokes shift and a much lower fluorescence quantum yield Φf. The huge Stokes shift originates from a considerable planarization in the excited state [42

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

• Christian Muschelknautz,
• Robin Visse,
• Jan Nordmann and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

• witnessed for the film absorption maxima of the 4-amino-prop-3-enylideneindolones 4 [30][32] the J-aggregation results in an induced emission [46][47] by Davydov splitting of the vibrationally relaxed lowest excited-state energy level [48][49] and causes a significant red shift of the sharp emission bands

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

• Dae Won Cho,
• Patrick S. Mariano and
• Ung Chan Yoon

Beilstein J. Org. Chem. 2014, 10, 514–527, doi:10.3762/bjoc.10.47

• reactions as a part of pathways leading to product formation. Thus, photochemical reactions promoted by excited state SET are governed by the chemical properties of charged and neutral radical intermediates [11][12][13][14][15][16][17]. A common pathway followed in reactions of ion radicals involves an α

• ][26][27][28][29][30][31][32][33][34]. In intensive early investigations, Kanaoka [35][36][37][38][39][40] and Colye [41][42][43][44] demonstrated the participation of phthalimides in several different kinds of interesting SET-promoted photochemical reactions. Since phthalimides have high excited state

• coupling (Scheme 3). Allyl- and enolsilanes serve as important substrates in numerous synthetically useful ground and excited state reactions [53][54]. The most common roles of these substances are to act as the respective equivalents of allylic anions and enolate ions. When coupled with strong

Studies on the photodegradation of red, green and blue phosphorescent OLED emitters

• Susanna Schmidbauer,
• Andreas Hohenleutner and
• Burkhard König

Beilstein J. Org. Chem. 2013, 9, 2088–2096, doi:10.3762/bjoc.9.245

• , possibly competing with the above mentioned reactive oxygen species-induced degradation route may proceed via the excited state of the emitter molecule. This might be due to instability of the excited molecule itself, via interaction of the excited molecule with its local environment or even other excited

• states [14][16][21]. Supposed the molecule is not susceptible to an attack of 1O2, it would be expected that the presence of oxygen in this case actually increases the photostability of the material. This is due to the very fast quenching of the excited state by O2 [22], leading to a significantly

• these two products could not be elucidated so far. Ir(ppy)3 In contrast, for the green emitting Ir(ppy)3 the presence of oxygen in benzene has a beneficial effect on the compound’s stability. This is likely due to the ability of oxygen to quench the triplet excited state of the complex, thus preventing

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• established that reductive quenching of the triplet excited state of Eosin Y by N-phenyltetrahydroisoquinoline 13 produced the Eosin Y radical anion. An ESR study on the irradiated solution of DMPO (5,5-dimethyl-1-pyrroline-N-oxide), Eosin Y, and N-phenyltetrahydroisoquinoline in air-saturated CH3CN detected

Topochemical control of the photodimerization of aromatic compounds by γ-cyclodextrin thioethers in aqueous solution

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2013, 9, 1858–1866, doi:10.3762/bjoc.9.217

• atom effect of the S-atoms of CD derivatives 1–7 should facilitate intersystem crossing to the triplet state and therefore support the formation of the anti-HH dimer. Because this preference does not hold true in this case, especially for host 2, the multiplicity of the excited state seems not to be

• the dominant factor, but rather the pre-organization of the guest molecules in the CD cavity prior to excitation has the greatest effect. The distribution of the stereoisomers appears to be mainly topochemically [5] controlled because of the short lifetime of the excited state of COU. Quantum

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• instant electron return and thereby maximize the number of radical pairs available for generating polarizations, a triplet sensitizer should be used [11]; the long life of a triplet excited state is also the only way to meet the conflicting requirements of bringing the self-exchange rates into the

• ], The fast component k0 in Equation 4 is the decay rate of the excited state whereas the slow component κ, comprises the effects of self-exchange (rate constant, kex; donor concentration, D0) and nuclear spin relaxation in the free radicals (relaxation time, T1). The latter spoils a perfect cancelation

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• medium-band-gap semiconductor and has proved to be an efficient photocatalyst for synthetic purposes [66][67]. It has been demonstrated that the excited state of g-C3N4, obtained by irradiation with visible light, is able to activate O2 to the corresponding superoxide radical. The latter could undergo

Incorporation of perfluorohexyl-functionalised thiophenes into oligofluorene-truxenes: synthesis and physical properties

• Neil Thomson,
• Alexander L. Kanibolotsky,
• Joseph Cameron,
• Tell Tuttle,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2013, 9, 1243–1251, doi:10.3762/bjoc.9.141

• that the excited state of T1-3FTh undergoes a greater conformational change before emission than that of T1-4FTh, which is further evidence of the greater planarity in the T1-4FTh ground state compared to that of its isomer. The optical HOMO–LUMO gaps were estimated from the onset of absorption and

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• (wavelengths λ, molar extinction coefficients ε), the excited-state processes, the reactivity of the produced radicals, and the characteristics of the light sources (emission spectra, available luminous power density) govern the polymerization efficiency (rate of polymerization, final monomer conversion). The

• potential of the donor, the reduction potential of the acceptor, the excited state energy and the coulombic term for the initially formed ion pair, respectively. C is neglected as usually done in polar solvents. Fluorescence experiments The fluorescence properties of the different Co_Pys were studied by

• wavelengths λmax,em), excited-state energy levels (ES), oxidation potentials (Eox) and free-energy changes ΔG (see text) [1]. Supporting Information Supporting Information File 2: Experimental procedures, characterization data, and additional spectra. Acknowledgements This work was partly supported by the

Synthesis, photophysical and electrochemical characterization of terpyridine-functionalized dendritic oligothiophenes and their Ru(II) complexes

• Amaresh Mishra,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2013, 9, 866–876, doi:10.3762/bjoc.9.100

• stabilities, and tunability of the excited-state energies [9]. Additionally, they can be employed as energy donor or acceptor units in electronic energy transfer processes [10]. In particular, ruthenium(II) polypyridine complexes have been extensively studied and represent an area of widespread interest that

• that arise from the population of a triplet luminescent level as the lowest excited-state after photoexcitation [14][15][16], and their derived multinuclear complexes are topologically interesting species including rods, wires, helicates, and dendrimer scaffolds [16][17][18][19][20][21][22]. In the

• (Φf ~ 10−3 to 10−4), the bands were attributed to the radiative deactivation of the lowest 3MLCT excited state of the Ru-based moieties [18][25][50]. It is interesting to note that for both metallodendrimers, 1 and 2, the emission bands are significantly red-shifted compared to the parent [Ru(tpy)2]2

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• reduced and an oxidized product is formed. As an example, the largely positive reduction potential of aromatic nitriles [5][8][9] and cyanophthalimides [10] in the singlet excited state or of aromatic esters in the triplet state [5][11] makes PET a common occurrence upon irradiation of such substrates in

• electrochemical measurements were carried out by a BASi computer-controlled electrochemical analyzer. The potentials measured were then referred to SCE, applying the equation E (versus SCE) = E (versus Ag/AgCl; 3 M NaCl) − 35 mV. The redox potential of the excited state of compounds TCB [8][9], DCN [8][9], DCA [8

• ][9], DCP [10] and DCP-ME [10] were taken from the literature, whereas the redox potentials of the excited state of 1,3,5-TrCB [21], 1,2,4-TrCB [21], ME [58] and PME [28] were determined by the Rehm–Weller equation [63]. Reduction potential (versus SCE) of the ground and excited state of acceptors and

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

• Sergei V. Chapyshev,
• Denis V. Korchagin,
• Patrik Neuhaus and
• Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

• triplet nitrenes 12–14 at the PBE/DZ level of theory. UB3LYP/6-311+G* orbital density in the LUMO of triazide 11 and CIS/6-311+G* orbital density in the highest singly occupied orbital of excited state 11a-S1*. Examples of selective photolysis of the azido groups. Possible photoproducts of triazide 11

Photoionisation of the tropyl radical

• Kathrin H. Fischer,
• Patrick Hemberger,
• Andras Bodi and
• Ingo Fischer

Beilstein J. Org. Chem. 2013, 9, 681–688, doi:10.3762/bjoc.9.77

• eV photon energy, i.e., 200 meV higher, which may correspond to either vibrational excitation of the first electronic excited state or to the next electronic state. A noisy feature appears at 10.7 eV, and is followed by the highest intensity peak at 11.6 eV. The most stable triplet state has been

• vertical excitation energies. The shoulder at 9.85 eV may thus either be due to the second triplet state, or to a vibrational fundamental of the excited state. For example a C–C stretching mode may be responsible for this peak, 1600 cm–1 further to the blue with respect to the first one. The electronic

• . The shoulder at around 10.7 eV in Figure 4 might be tentatively assigned to this state. However, previous calculations predicted the first singlet excited state at photon energies of 11.3 [9] and 11.74 eV [45]. Our EOM-CCSD result at 11.07 and TD-DFT results at 11.09, 11.24 and 10.95 eV with the B3LYP

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• substrates but must not be a strong UV absorber itself. Other factors to consider are that the solvent should not undergo quenching or hydrogen-atom abstraction or other reactions with the excited state (although some solvents can be useful sensitisers, e.g., acetone). Acetonitrile has proved to be a

Palladium-catalyzed C–N and C–O bond formation of N-substituted 4-bromo-7-azaindoles with amides, amines, amino acid esters and phenols

• Rajendra Surasani,
• Dipak Kalita,
• A. V. Dhanunjaya Rao and
• K. B. Chandrasekhar

Beilstein J. Org. Chem. 2012, 8, 2004–2018, doi:10.3762/bjoc.8.227

• -deficient pyridine ring. The pKa value of 7-azaindole is ~4.9, and it undergoes self-association through hydrogen-bonding to form a dimer in solution and phototautomerizes by an excited-state double-proton-transfer (ESDPT) process [1][48]. In the presence of copper or palladium catalysts azaindole undergoes

Cyclodextrin nanosponge-sensitized enantiodifferentiating photoisomerization of cyclooctene and 1,3-cyclooctadiene

• Wenting Liang,
• Cheng Yang,
• Masaki Nishijima,
• Gaku Fukuhara,
• Tadashi Mori,
• Andrea Mele,
• Franca Castiglione,
• Fabrizio Caldera,
• Francesco Trotta and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2012, 8, 1305–1311, doi:10.3762/bjoc.8.149

• intermolecular interactions, short lifetime and high reactivity of the excited-state substrate are the major causes that prevent efficient asymmetric induction in chiral photochemistry. A supramolecular approach to photochirogenesis provides a convenient and also promising tool to facilitate the excited-state