Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• of ICT for electronic state modification in the excited state of the molecules [45]. In this state, all dyes have a notably higher dipole moment and a lower LUMO energy level as compared to their ground state [46][47][48][49]. Increasing the electron-donating strength of the various heterocyclic

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• cleavage reactions [80] and 1,5-HAT [81] and iii) the excited state of the simple organic molecule target can possess an ultrashort lifetime [82] that precludes photochemistry in favor of photophysical or nonradiative deactivation, e.g., fluorescence or internal conversion (IC). Instead of direct UV

• ). An unfortunate consequence of this is that there are many organic molecules with redox potentials that lie beyond the range of those of the excited photocatalyst [87]. The transiently generated (ultralow concentration of) the excited-state catalyst does not persist long enough even for slightly

• which the excited state photocatalyst participates directly in HAT with the substrate (Scheme 2B), herein termed PHAT [88]. iii) Photochemical reactions where the photosensitization catalyst (PSCat) engages in Dexter energy transfer (typically TTET) with the substrate (or fluorinating reagent) to induce

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• , the obtained fulgides/fulgimides after exposure to light of 365 nm irreversibly rearrange into the colorless closed isomers, 3a,4-dihydronaphtho[2,3-c]furan-1,3-diones 9 and 10 and 3a,4-dihydro-1H-benzo[f]isoindol-1,3(2H)-diones 11 and 12. These are formed due to the symmetry-allowed excited state

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• activation step to produce a palladacyclic intermediate. In parallel, the oxidative decarboxylation of the α-ketoacid induced by the photocatalyst in its excited state generates the corresponding acyl radical. The latter is intercepted by the palladacycle, leading to a Pd(III) species. Remarkably, the

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• measurements, TRPL spectroscopy, and density functional theory (DFT) calculations. They found that the HER efficiency correlated to the excited state lifetime and exciton binding energy. The FSO-BP and FSO-FSz hindered the charge transfer and mobility due to the phenyl–phenyl dihedral angle or sharp bends in

• the polymer chain, whereas the FSO-F and FSO-FS polymers had ridged planar chains that facilitated the charge transfer [129]. The FSO-FS dibenzothiophene unit had an extended conjugation onto the sulphur atom in the excited state, which improved the charge delocalisation [129]. This demonstrated that

• shown by Ji, Zhao, Jacquemin, and co-workers [130], and may have contributed to extending the excited state lifetime and reducing the binding energy of excitons in FSO-FS relative to FSO-F. 2.3 Immobilised molecular photocatalysts A strategy that combines many of the benefits of homogenous and

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• -Diphenylsilacyclopentadiene (324) underwent a photo-induced [2 + 2] cycloaddition with CS2 to afford two regioisomeric fused thietane-2-thiones 325 and 326. The electron transfer from the singlet-excited state of silacyclopentadiene to CS2 was shown to play an important role in the cycloaddition [90] (Scheme 61). 3.1.2

• to proceed via an n–π* triplet-excited state [96] (Scheme 70). In 1993, the same group first attempted to prepare a chiral thietane-fused β-lactam 356a from an achiral monothioimide 355a using a chiral crystal environment through a topochemically controlled intramolecular photochemical [2 + 2

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• case (Scheme 1, box 2), the excited photocatalyst can engage in an EnT mechanism. Upon the excitation and intersystem crossing, the triplet state photocatalyst 3PC* can interact directly with a ground state species Sub and transfer the triplet energy to generate an excited state Sub* and the ground

• state PC. In most cases, Sub* is in the triplet state if it is an organic molecule. A common exception to this is molecular oxygen, which upon excitation attains a more reactive singlet state. In the third mode of activation, atom transfer (AT, Scheme 1, box 3), the excited state photocatalyst PC* can

• difficult to be directly activated by the excited state photocatalyst. For these reasons, the photocatalyzed decarboxylation often proceeds on the corresponding carboxylates, which are easier to be oxidized. This photoinduced SET, followed by the loss of CO2 as the sole byproduct, gives access to the

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• deactivation process from the lowest singlet (S1) excited state to the ground (S0) state [9]. Interestingly, for such π-conjugated molecules, suitable structural modifications can switch the radiative S1→S0 process to another radiative deactivation process from the triplet (T1) excited state to S0 via an S1→T1

• fluorescence via radiative deactivation from the S1 excited state to the S0 state and phosphorescence via electronic transition from the T1 excited state to the S0 state, respectively. Accordingly, fluorinated benzils and bisbenzils show room-temperature phosphorescence in the solution state. To understand the

• being conducted to better understand the photophysical mechanisms of the excited-state dynamics of these benzil and bisbenzil derivatives. Conclusion In this article, we described the design and synthesis of benzil- or bisbenzil-based room-temperature phosphorescent molecules via a simple oxidation

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds

• Rasa Keruckiene,
• Simona Vekteryte,
• Ervinas Urbonas,
• Matas Guzauskas,
• Eigirdas Skuodis,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 1142–1153, doi:10.3762/bjoc.16.101

•  5a). To assist in the analysis of the spectra, natural transition orbitals (NTO) for the S1 state were generated. Figure 6 shows the pairs of electron–hole NTOs for the relaxed S1 excited-state geometry. These orbitals indicate which changes in electronic density occur upon relaxation. For all three

• energy values at the corresponding excited-state geometry. The time-dependent DFT (TD-DFT) calculations were carried out with the Gaussian 16 software package and molecular orbitals were visualized by using Gaussview. Photoelectron emission spectroscopy measurement was performed according to the

• thin films of compounds 1–3 (λexc = 350 nm and PL decay curves (b) of thin films of derivatives 1–3 recorded at different emission wavelengths. Electron and hole NTOs of compounds 1–3 in the S1 excited state (vacuum). Chemical structures of exciplex-forming materials used, and visualization of white

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

• Nuray Altinolcek,
• Ahmet Battal,
• Mustafa Tavasli,
• William J. Peveler,
• Holly A. Yu and
• Peter J. Skabara

Beilstein J. Org. Chem. 2020, 16, 1066–1074, doi:10.3762/bjoc.16.93

• solvents are shown in Figure 6. Upon excitation at π–π*/n–π* bands (λexc= 245–349 nm for 7a and 248–356 nm for 7b), the PL spectra of compound 7a in most solvents depicted dual emission bands, one from the locally excited state and one from ICT. On the other hand, the PL spectra of compound 7b in most

• . This indicates that the excited state dipole moment is much greater than the ground state dipole moment. Quantum yields The relative fluorescent quantum yields (ϕFL) of compounds 7a and 7b were determined in dichloromethane by using rhodamine B (ϕFL = 49% at λexc=355 nm) in ethanol as reference [45

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• porphyrin is in the triplet excited state, two distinct processes can be observed: a) single electron transfer (SET); and b) energy transfer (Figure 2) [12][13][14]. The first involves the exchange of electrons between the porphyrin and the substrate by an oxidative or reductive process, and the second

• , respectively (both vs saturated calomel electrode (SCE)). These data indicate that the excited state of TPP is a more efficient electron donor than its ground state. At the same time, the reduction potential value suggests that the excited state of TPP (E1/2(TPP*/TPP−•) = +0.42 V vs SCE) is a more efficient

• this transformation involves the formation of an aryl radical by SET between the diazo compound and the porphyrin in its excited state (Scheme 3). The authors demonstrated that meso-arylated porphyrins can efficiently act by an oxidative quenching. However, issues about why an electron-poor porphyrin

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• up to 67%, while their bandgaps and chiroptical responses could be tuned by twisting the bipyrrole chromophore. The solvatochromism and apparent superradiance of these chromophores indicated a potential involvement of solvent-induced symmetry-breaking charge transfer in the excited state [34]. Here

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• , which were more stable than the undeuterated ones upon irradiation and subsequent excitation [27][28]. The excited triplet state T1 (n,π*) of carbonyl compounds tends to be the most reactive state (compared to the singlet state). Furthermore, this excited state is easily accessible, as the quantum yield

• Norrish type I reactions, forming two radicals, 47 and 48 (reaction (1) in Scheme 12), or abstracted a hydrogen atom from a ketone/aldehyde monomer, forming a monomeric radical and an alcohol radical 49 (reaction (2) in Scheme 12). The excited state of the hydrates 45 and 46, in an aqueous solution may

• -anisaldehyde (52), 4-cyanobenzaldehyde (53), and 2,4-dimethoxybenzaldehyde (54), all three of which showed strong absorption bands below 340 nm. As shown in Scheme 14, the excited state 55 of the benzaldehyde derivatives 52–54, respectively, that occurred after irradiation could reduce perfluoro-1-iodohexane

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• fluorescence quantum yields of 3a and 4a remain high (Φf = 0.95 and 0.56, respectively) and are comparable to that of 1a (Table 1). The smaller Stokes shift values of ≈178 cm−1 and longer emission lifetimes of ≈7.83 ns indicate the rigid scaffolds of α,α-disubstituted 4a in the excited state. In the case of β

• . The mesomeric effect on the ethynyl substituents at the β-position of the BODIPY core is thus different from the α-substituted ones. Furthermore, to understand the excited-state properties (e.g., Stokes shifts) of the substituted BODIPYs, the S1-state geometries for 4a and 6a were obtained by the time

• -dependent (TD) DFT methods. As a result, the excited-state structure of 6a exhibits a remarkably bent distortion of the core with a plane angle of 16.1°, whereas the structure of 4a remains coplanar (Figure S25, Supporting Information File 1). The corresponding energy gap between the HOMO and LUMO of 6a is

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• suggested a possible mechanism based on the measured and reported redox potential (Scheme 1). Upon irradiation at 530 nm using green light, the Cu(I) catalyst transitions to an excited state. Then, the excited copper complex transfers an electron to the alkyl halide, which can generate an alkyl radical that

• green light, the Cu(I) catalyst transitions to the excited state. Then, the excited copper complex undergoes an electron transfer to CF3SO2Cl, allowing the formation of the CF3 radical, and the resulting Cu(II) species binds to the SO2Cl anion, known to be unstable when free. Then, the CF3 radical adds

• examples. Indeed, they usually possess an increased lifetime of the triplet excited state due to a particular geometry that prevents the reorganization from a tetrahedral geometry in the ground state to a square planar geometry [31]. Moreover, the synthesis of these compounds is usually facile, and they

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

• 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

• excited state possesses several competitive reaction pathways for deactivation. This is a photochemical reaction such as photoinduced electron transfer serving as source to generate reactive intermediates such as initiating radicals or conjugate acid [5]. Photophysical events of S1 occurring after one

• . Furthermore, chain extension and block copolymerization experiments confirmed the chain end fidelity and therefore the living character of polymerization (Table 3, Figure 4). On/Off experiments demonstrated the light dependency of polymerization [81]. The proposed mechanism (Figure 5) involves the excited

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• their oxidized/reduced forms) can perform both opposed redox events before returning to their original oxidation state for re-excitation. If no substrate is encountered during the lifetime of the excited state the ground state is typically regenerated. Such photogenerated radical intermediates can be

• voltammetry to determine the oxidation potential (EOx) of monochloroacetic acid in acetonitrile (Figure 2). This way it could be verified, if monochloroacetic acid can quench the excited state of one of the common photoredox catalysts. In Figure 1 the cyclic voltammogram of monochloroacetic acid is shown. One

• in its excited state [35]). The weak C–H bond of acetonitrile (93.0 kcal mol−1) compared to the C–H bond strength of a carbonyl α-C–H bond (94.1 kcal mol−1) resulted in formation of 2 (2,2,6,6-tetramethylpiperidin-1-yl)oxyacetonitrile (compound 2; Scheme 3) [36]. Hence, to avoid the reaction with the

Six-fold C–H borylation of hexa-peri-hexabenzocoronene

• Mai Nagase,
• Kenta Kato,
• Akiko Yagi,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2020, 16, 391–397, doi:10.3762/bjoc.16.37

• from the singlet excited state were determined (kr = 2.0 × 106 s−1; knr = 7.9 × 107 s−1). The frontier molecular orbitals of 1 calculated by DFT calculations at the B3LYP/6-31G(d) level of theory are shown in Figure 4b. Owing to the highly symmetrical structure of 1, both its HOMO and HOMO−1 as well as

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• the radical τ = 1ps. This is in complete agreement with the prediction made by McBurney and Walton [51] for the decarboxylation of N-arylcarbamoyloxyl radicals where they were expected to decarboxylate with great rapidity having almost no finite lives. Excitation of 12 to the singlet excited state (S1

• ) forces the molecule to pass over an energy barrier of approximately 7 kcal/mol dissociating further and giving ground state radicals again. For the photodissociation of 11 from either electronic excited state (T1, S1) calculations show that this is not possible since in this case the intervening energy

• triplet state energy activators are compounds that have the ability to be efficiently excited to their triplet excited state. TPSs may be used, among others, to transfer their triplet energy to other molecules that have a low yield of intersystem crossing (ISC) and inefficient production of triplet state

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• into chemical energy via the generation of reactive intermediates through electron transfer reactions. A photochemical reaction is directed by the photophysical properties of an electronically excited molecule. The first vibrational equilibrated singlet excited state is S1, and it depends on both

• hand, S1 can also transition to the spin-forbidden T1 through intersystem crossing (ISC), which then decays by (longer) radiative processes to S0 (phosphorescence. Figure 3) [41][42][43]. The triplet excited state is oxygen-sensitive as O2 carries out quenching in solution, thereby leading to the

• . Furthermore, it has also been observed that the excited-state species are more oxidizing or reducing than the species in the ground state. This is due to the availability of the half-empty low-energy orbital and the presence of an electron in a high-energy orbital, respectively [49][50]. Review Why photoredox

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• restricted conformational flexibility. As a result, conformational changes of the styryl substituent in the excited state that lead to radiationless deactivation in solution were significantly suppressed within the binding site so that emission became competitive. The DNA-binding properties of the ligands 3a

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• the donor and the acceptor. Compounds 2, 4, and 5 were very poorly luminescent and so their emission could not be quantified. Compound 3 exhibited a broad and unstructured emission in a degassed DCM solution (λPL = 550 nm), characteristic of an excited state with significant CT character. The

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• the differences observed, differences in the excited-state profiles and quantum yields for the photoisomerization pathway may also contribute to the lack of correlation between band overlap and photoisomerization efficiency [35]. Conclusion We aimed to combine two features now known to significantly

• the lowest-lying singlet excited state and the ground state at the transition state geometry for 4pzH and 4pzMe. Theoretical calculations at the PBE0-D3/6-31G** level indicate that the lowest-lying S1 state lies >1 eV above in energy with respect to the ground state, and therefore the DFT approach is

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• excited state [59]. Plotting Stokes shifts Δν̃ against the orientation polarizabilities Δƒ of the respective solvents (Lippert plot) [60] gives a reasonable linear correlation with a moderate fit of r2 = 0.970 (Figure 13). The orientation polarizabilities Δƒ were calculated according to Equation 1 where

• εr is the relative permittivity and n the optical refractive index of the respective solvent. The change in dipole from the ground to the excited state can be calculated according to the Lippert–Mataga equation (Equation 2) where ν̃abs represents the absorption and ν̃em the emission maxima (in m−1

• the solid state. This finding suggests that by restricting intramolecular motion and vibration, which enables radiation-less deactivation of the excited state [61], an AIE (aggregation‐induced emission) or AIEE (aggregation-induced enhanced emission), might become operative [62][63][64]. The AIE or

Plasma membrane imaging with a fluorescent benzothiadiazole derivative

• Pedro H. P. R. Carvalho,
• Jose R. Correa,
• Karen L. R. Paiva,
• Daniel F. S. Machado,
• Jackson D. Scholten and
• Brenno A. D. Neto

Beilstein J. Org. Chem. 2019, 15, 2644–2654, doi:10.3762/bjoc.15.257

• agreement with the experimental data and helped to understand the stabilizing intramolecular charge-transfer process from the first excited state. The new fluorescent derivative could be applied as selective bioprobe in several cell lines and displayed plasma-membrane affinity during the imaging experiments

• and first excited state S1 (∆ρ = ρS1 − ρS0), as shown in Figure 4D, highlights the directionality of the electron density transfer with a great deal of ICT between the cationic heterocycle and the BTD core, which stabilizes the excited state of the synthesized chromophore. These theoretical results