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

• excited state energy and redox potentials to interact with additives [13]. Parallel to this, the environmental issues impose the use of new polymerization methods that are safer for the manipulator, contribute to lower the amount of released volatile organic compounds and can reduce the energy consumption

• electronically excited state which significantly changes the distribution of electrons in the molecule. Thus, chemical properties such as reactivity, oxidation potential or reduction potential change drastically. With appropriate donors or acceptors, electron charge transfer is possible via this excited state

• photoredox catalyst in the visible range, several parameters have to be fulfilled: [17] i) The molecule should strongly absorb in the near UV or visible range with high molar extinction coefficients. ii) The redox potentials of the excited state of photoredox catalysts must be in appropriateness to those of

Photocatalyic Appel reaction enabled by copper-based complexes in continuous flow

• Clémentine Minozzi,
• Jean-Christophe Grenier-Petel,
• Shawn Parisien-Collette and
• Shawn K. Collins

Beilstein J. Org. Chem. 2018, 14, 2730–2736, doi:10.3762/bjoc.14.251

• providing 2 (54–87% yield, not including dppf-based complexes). Interestingly, the best catalyst for the transformation (Cu(tmp)(BINAP)BF4, 99% of 2) was a poor catalyst for a previously reported photoredox reaction [27]. It should be noted that Cu(tmp)(BINAP)+ possesses an excited state reduction potential

• of −1.93 V vs. SCE, much greater than that of Ru(bpy)3+2 (−0.81 V vs SCE), albeit the copper complex has a much shorter excited state lifetime (≈4 ns vs ≈1100 ns for Ru(bpy)3+2). The excited state reduction potential should match favorably with CBr4 (E½ = 0.30 V vs SCE) in DMF [29]. Note that many of

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• with time-resolved photoluminescence spectroscopy revealed that the oxidative quenching of the excited state of Irdfppy favorably proceeds over the reductive quenching mechanism. The combination of 1 and Irdfppy offers the best choice for the dechlorination of DDT among our light-driven systems in

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• (dtbpy)]PF6 as the photocatalyst. The reaction was carried out under nitrogen under visible-light irradiation at 455 nm. The oxidation potential of this test arene is 1.02 V vs SCE, which allows oxidation by [Ir(dF(CF3)ppy)2(dtbpy)]PF6 having an estimated excited state oxidation potential of 1.21 V vs

• addition of 1,2,4-trimethoxybenzene (oxidation potential 1.02 V vs SCE, Figure 3a). The values are similar to the estimated excited state oxidation potential of [Ir(dF(CF3)ppy)2(dtbpy)]PF6 ( +1.21 V vs SCE in acetonitrile). On the other hand, the luminescence was quenched negligible on addition of diphenyl

• )]PF6 and also did not give a sulfenylated product under our photocatalytic conditions. This is rationalized by the oxidation potential of anisole of 1.76 V vs SCE, which is higher than the estimated excited state oxidation potential of the photocatalyst. To elucidate, if the 1,3,5-TMB radical cation

Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

• Liudmila L. Rodina,
• Xenia V. Azarova,
• Jury J. Medvedev,
• Dmitrij V. Semenok and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2018, 14, 2250–2258, doi:10.3762/bjoc.14.200

• with up to 90–97% yield. Keywords: C–H insertion; diazo compounds; excited state; photochemistry; Wolff rearrangement; Introduction Photochemical reactions of diazocarbonyl compounds are well-known transformations in the synthesis of the diversified acyclic, carbo- and heterocyclic structures [1][2

• long wavelength bands are most likely caused by n–π* transitions. Based on the position of the long wavelength bands (363–367 nm) the energy of the singlet excited state 1S1 of diazodiketones 1 can be estimated at about 78–79 kcal/mol [41]. The characteristics of the absorption bands of the sensitizers

• energy of the triplet excited state 3T1 of this sensitizer (64 kcal/mol) is somewhat lower than the corresponding energy of the diazodiketones 1 making it inadequate to initiate the C–H insertion reaction. On the other hand, the triplet excited state energy of benzophenone (69 kcal/mol) renders it a

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

• photophysical overview. There are several factors that affect the ability of an organic molecule to act as a photocatalyst. In a typical organocatalysed photoredox reaction, the photocatalyst transitions from a singlet ground state (S0) to a long-lived and relatively stable excited state, either a singlet

• 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

• energy of the excited state of the catalyst. Catalysts with a λmax at a longer wavelength have excited states at relatively low energy and therefore do not have very strong oxidising or reducing capabilities. A good balance is achieved by molecules which have λmax in the visible region. Many organic

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

• shift in CHCl3. This effect is presumably caused by a charge shift (CS) or, more likely, by a charge transfer (CT) in the excited state from the electron-donating aryl unit to the excited quinolizinium (Scheme 3) [57], which has been proposed also to take place in structurally resembling excited biaryl

• 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

• ct DNA with the methoxy-substituted derivative 2b led to an increase of the low emission intensity by a factor of 3 (Figure 8B). Although this effect is rather small, it indicates the suppression of a deactivation pathway in the excited state upon the accommodation of 2b in a constrained binding site

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

• excited state lifetime of conjugate 9 as function of the concentration of guanosine monophosphate (GMP, Figure 4). Stern–Volmer analyses indicate that a dynamic quenching is occurring, with a quenching rate close to the diffusion limit (kQ = 5.6 108 M−1s−1 in intensity and kQ = 5.3 108 M−1s−1 in lifetime

• of GMP, the transient absorption spectrum of conjugate 9 is dominated by the luminescence, the ground state bleaching and some excited state absorption around 340 nm whereas in the presence of GMP a positive transient signal can be observed around 500 nm on a long time scale. This transient is

• -calix[4]arene-[c-(RGDfK)]4 conjugate 9 in water. Luminescence intensity and excited state lifetime of conjugate 9 in the presence of GMP measured in 10 mM Tris·HCl buffer at pH 7.0. Transient absorption spectra of RuII-calix[4]arene-[c-(RGDfK)]4 conjugate 9 (in 10 mM Tris·HCl buffer at pH 7.0) measured

The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking

• Dominic Bernhard,
• Fabian Dietrich,
• Mariyam Fatima,
• Cristóbal Pérez,
• Hannes C. Gottschalk,
• Axel Wuttke,
• Ricardo A. Mata,
• Martin A. Suhm,
• Melanie Schnell and
• Markus Gerhards

Beilstein J. Org. Chem. 2018, 14, 1642–1654, doi:10.3762/bjoc.14.140

• this level of theory for the similar diphenyl ether–methanol system [19]. Furthermore, the obtained structures were re-optimized with the SCS-CC2 method using the def2-TZVP basis set, both in the electronic ground (S0) and first excited state (S1). The ricc2 module in Turbomole 7.0 requires an

• somewhat underestimate the stability of OH∙∙∙O contacts. Electronically excited state spectrum For the investigation of the electronically excited state by using the UV/IR/UV technique, a two-color R2PI signal is required. For this reason, the one-color R2PI signal was suppressed by attenuating the laser

• temporally overlapping laser pulses, the spectrum contains transitions from the S0 state, the electronically excited (S1, at 3637 cm−1) and also the ionic D0 state (at 3667 cm−1). This could not be avoided, as the lifetime of the excited state, which is estimated to be in the order of 5–7 ns, is shorter than

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• phosphorescent organic light-emitting diodes (PhOLEDs) and light-emitting electrochemical cells (LEECs). This interest is driven by the fact that luminescent TMCs with long-lived excited state lifetimes are able to efficiently harvest both singlet and triplet electro-generated excitons, thus opening the

• strategy to obtain luminescent platinum(II) complexes has been the use of π-conjugated chelating ligands with a bidentate motif bearing π-accepting (hetero)aromatic units. Compared to monodentate ligands, the more rigid structure of the bidentate motif is expected to reduce excited-state molecular

• solution. On the contrary, they became strong emitters in the solid state owing to the switching of the nature of the excited state that becomes 3MMLCT in nature. Their EL properties were evaluated by fabrication of non-doped OLEDs. Compound 10 was embedded into an OLED device with the following

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• (299) in good yield as a major product. The formation of this product has been described either by the initial formation of 298 followed by rearrangement or by a mechanism with 241B as an intermediate. Also, Aihara’s group reported excited-state intramolecular proton transfer (ESIPT) and aromaticity

An uracil-linked hydroxyflavone probe for the recognition of ATP

• Márton Bojtár,
• Péter Zoltán Janzsó-Berend,
• Dávid Mester,
• Dóra Hessz,
• Mihály Kállay,
• Miklós Kubinyi and
• István Bitter

Beilstein J. Org. Chem. 2018, 14, 747–755, doi:10.3762/bjoc.14.63

• electric fields generated by ions and molecules in solution. This property along the ESIPT process (excited state intramolecular proton transfer) [35] makes them ideal for ratiometric environment-sensitive probes and sensors [36][37][38][39][40][41][42][43]. Among them the 4’-dimethylamino derivative (DMHF

D–A–D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies

• Lin Gan,
• Xianglong Li,
• Xinyi Cai,
• Kunkun Liu,
• Wei Li and
• Shi-Jian Su

Beilstein J. Org. Chem. 2018, 14, 672–681, doi:10.3762/bjoc.14.55

• different configurations have a serious effect on the photoluminescence and electroluminescence performance according to the change in singlet–triplet splitting energy (ΔEST) and excited state geometry. This indicates that a better configuration design can reduce internal conversion and improve triplet

• basis of the previous considerations, for TADF materials, the energy difference (ΔEST) between the first singlet excited state (S1) and the first triplet excited state (T1) must be small enough to enable the RISC process with the activation of environmental thermal energy [5]. To achieve this, electron

• energy levels, are calculated from Ered and Eox. Compounds 1 and 2 have similar HOMO and LUMO energy levels due to the same donor and acceptor in the molecules (Table 1). The molecular geometry of 1 and 2 in the ground state and excited state were simulated by density functional theory (DFT) and time

Polarization spectroscopy methods in the determination of interactions of small molecules with nucleic acids – tutorial

• Tamara Šmidlehner,
• Ivo Piantanida and
• Gennaro Pescitelli

Beilstein J. Org. Chem. 2018, 14, 84–105, doi:10.3762/bjoc.14.5

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• authors propose that the photo-excited state of the organic dye Eosin Y is reductively quenched by the aryl thiol to form the Eosin Y radical anion and the respective aryl thiyl radical cation. Neutral Eosin Y is regenerated through oxidation of the radical anion by dioxygen. The resulting superoxide

• steps. Applying the organic dye Eosin Y as photocatalyst avoids this problem. The single-electron oxidation of aryl thiols by the excited state of Eosin Y is thermodynamically feasible and forms a thiyl radical cation, which subsequently can be deprotonated by pyridine to the respective thiyl radical

• different strategy for the photoredox-catalyzed preparation of diaryl sulfides was reported in 2013, applying [Ru(bpy)3]Cl2 as photocatalyst (Scheme 16) [47]. The authors propose a mechanism where in situ generated aryl diazonium salts are cleaved by reduction of the excited state of the photocatalyst to

Halogen-containing thiazole orange analogues – new fluorogenic DNA stains

• Aleksey A. Vasilev,
• Meglena I. Kandinska,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• David Sucunza,
• Juan J. Vaquero,
• Obis D. Castaño,
• Stanislav Baluschev and
• Silvia E. Angelova

Beilstein J. Org. Chem. 2017, 13, 2902–2914, doi:10.3762/bjoc.13.283

• it is not sensitive to the type of substituent in the series, thus suggesting similar transition type and geometry of the Franck–Condon excited state. It can be seen from the results in Table 1 that the replacement of a hydrogen atom with an electron-withdrawing group at the C-7 position in the

• for deactivation of the excited state [43]. The replacement of the hydrogen atom at the C-5 position in the benzothiazole side of the molecules with a bromo substituent does not have any significant influence on the fluorescence of dyes 5c and 5d, which is similar to its effect on the absorption

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• reduction potential of Cu(dap)2Cl in the excited state, and its important ability to mediate the transfer of the Cl atom. Consequently, a variety of electron-deficient alkenes, such as N-arylacrylamides, acrylonitrile, acrylate and enone derivatives furnished their chlorotrifluoromethylated analogues in

Development of a fluorogenic small substrate for dipeptidyl peptidase-4

• Futa Ogawa,
• Masanori Takeda,
• Kanae Miyanaga,
• Keita Tani,
• Ryuji Yamazawa,
• Kiyoshi Ito,
• Atsushi Tarui,
• Kazuyuki Sato and
• Masaaki Omote

Beilstein J. Org. Chem. 2017, 13, 2690–2697, doi:10.3762/bjoc.13.267

• from THF to H2O/DMSO (9:1) as shown in Figure 2 and Table 3. The fluorescence quantum yield of a fluorophore generally decreases significantly in an aqueous solvent because of release of energy in the excited state of the fluorophore by forming hydrogen bonds with water. However, in the cases of 1 and

Pyrene–nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies

• Artur Jabłoński,
• Yannic Fritz,
• Hans-Achim Wagenknecht,
• Rafał Czerwieniec,
• Tytus Bernaś,
• Damian Trzybiński,
• Krzysztof Woźniak and
• Konrad Kowalski

Beilstein J. Org. Chem. 2017, 13, 2521–2534, doi:10.3762/bjoc.13.249

• carbonyl compound 3 as compared to the hydroxy compound 5. The computations reveal several triplet states below the lowest singlet excited state. In particular, the carbonyl pyrene derivative 3 displays a triplet state of nπ* character being lower in energy than the emissive singlet state S1 (being a

• level. “Holes” (starting orbitals) and “electrons” (final orbitals) represent natural transition orbitals [32][33] describing each excited state. Self-assembly ratios of 3 and 5 with single-stranded templates (dA)10, T10 and double strand (dA)10-T10 under pure aqueous (no salts) and buffer conditions

One-pot syntheses of blue-luminescent 4-aryl-1H-benzo[f]isoindole-1,3(2H)-diones by T3P^® activation of 3-arylpropiolic acids

• Melanie Denißen,
• Alexander Kraus,
• Guido J. Reiss and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2017, 13, 2340–2351, doi:10.3762/bjoc.13.231

• can be detected and monitored by absorption and emission spectroscopy. Furthermore, the investigation of a substance library of various 2,3- and 1,8-naphthalene imides has shown that the electronic nature of the ground and the excited state is decisively influenced by variation of the substitution

• vibrationally relaxed excited state. This is even more the case in the nearly perfect linear correlation of the Stokes shift with σR (r2 = 0.989) and can be interpreted as a significant structural change upon photonic excitation and excited state relaxation resulting from a considerable charge transfer

New electroactive asymmetrical chalcones and therefrom derived 2-amino- / 2-(1H-pyrrol-1-yl)pyrimidines, containing an N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment: synthesis, optical and electrochemical properties

• Daria G. Selivanova,
• Alexei A. Gorbunov,
• Olga A. Mayorova,
• Alexander N. Vasyanin,
• Igor V. Lunegov,
• Elena V. Shklyaeva and
• Georgii G. Abashev

Beilstein J. Org. Chem. 2017, 13, 1583–1595, doi:10.3762/bjoc.13.158

• ], which exhibit the redshift of a longwave absorption/emission maxima along with the increase of a solvent polarity. Maybe this is a result of a molecule symmetry breaking in its excited state [27]. Taking into account all the factors mentioned above, we have started the investigation of solvatochromic

• absorption maxima and of fluorescence maxima as well, and in the last case this shift is more pronounced. This indicates that the excited state of the molecule is more polar than the ground state, and, therefore, when a solvent is replaced by a more polar one, a large stabilization of the excited state in

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

• carbohydrate-derived CD to date. Interestingly, it was observed that the fluorescence of these N/P-CDs was strongly dependent on the local concentration of Fe3+. With increasing concentrations of the metal leading to fluorescence decay of the CDs, which was attributed to the interception of an excited state on

Synthesis and optical properties of new 5'-aryl-substituted 2,5-bis(3-decyl-2,2'-bithiophen-5-yl)-1,3,4-oxadiazoles

• Anastasia S. Kostyuchenko,
• Tatyana Yu. Zheleznova,
• Anton J. Stasyuk,
• Aleksandra Kurowska,
• Wojciech Domagala,
• Adam Pron and
• Alexander S. Fisyuk

Beilstein J. Org. Chem. 2017, 13, 313–322, doi:10.3762/bjoc.13.34

• ). Moderate to large values of Stokes shifts are observed for compounds 15b–g originating from bond order switching (benzenoid to quinoid) in the excited state. Moderate values of Stokes shifts (0.52–0.63 eV) are observed for 15b–e and the Stokes shift increases with an increase of the aryl substituent size

• tools for the investigation of both ground and excited-state properties of various organic and inorganic compounds [30][31]. However, it has been shown that the description of π–π* transitions for bithiophene derivatives of 1,3,4-oxadiazoles still remains challenging. Grimme and Dierksen [32] have

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• excited state is very low and is strongly dependent on the permanent magnetic field (B0) applied. This limitation is compensated by using stronger magnetic fields, which results in more complex, large and expensive NMR instruments and/or the development of specialized probes. Although the low sensitivity

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

• Jonas Becher,
• Daria V. Berdnikova,
• Darinka Dzubiel,
• Heiko Ihmels and
• Phil M. Pithan

Beilstein J. Org. Chem. 2017, 13, 203–212, doi:10.3762/bjoc.13.23

• red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pKa = 7.9), it has a strongly increased acidity in the excited state (pKa* = 0.4). As a result

• observed for the excited-state proton transfer (ESPT) of so-called photoacids. The latter are weak acids in the ground state, whereas their acidity in the excited state increases significantly [25][26][27]. As the activity of photoacids is triggered by light, they have a great potential to be employed as

• proton sources with high local and temporal control. In this context, it was shown that the excited state acidity of organic photoacids such as topotecan, pyrrolylphenylpyridine, hydroxyacetonaphthone, or hydroxybenzimidazole changes considerably on complexation with cucurbiturils [28][29][30][31][32][33