Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• radical mechanism in which the iminoxyl radical is generated from the oxime anion under the action of perfluorobutyl iodide through the formation of an EDA complex (electron donor–acceptor complex, which is also called charge-transfer complex). The perfluorobutyl radical formed at this step served for the

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

• to a quasi-orthogonal geometry of the donor part on the acceptor core, and the charge-transfer (CT) character [16]. On the other hand, not adapting the vertical dihedral angle enabled a slight HOMO and LUMO overlap in the geometry of compound 1. This resulted in a higher oscillator strength of 0.0109

• moieties, respectively [19]. Additionally, a weak absorption band (shoulder) at ca. 348 nm was detected for compound 2, evidencing an intramolecular charge transfer (ICT) between the phenothiazine and quinazoline units. The energy band gap values determined from the edges of the experimental UV spectra of

• compounds, the transition took place between orbitals delocalized over both donor fragments and the quinazoline moiety indicating a charge transfer in vacuum. Considering the experimental data, it could be presumed that this 1CT state is very sensitive and easily quenched in polar solvents as it competes

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

• distinctive absorption bands: high and mid energy bands due to locally excited (LE) transitions and low energy bands due to intramolecular charge transfer (ICT) transitions. In dichloromethane solutions compounds 7a and 7b gave emission maxima at 561 nm and 482 nm with quantum efficiencies of 5.4% and 97.4

• Fluorescence and Absorbance Spectrometer. Each compound (7a/7b) displayed three distinctive absorption bands in the UV–vis spectra: high energy bands and mid energy bands were assigned to π–π* and n–π* transitions, whereas the low energy bands were assigned to an intramolecular charge transfer (ICT) transition

• dependent on the excitation wavelength chosen and the solvent used. It is believed that the dual emission was due to mixed locally excited (LE) and intramolecular charge transfer (ICT) states and the single emission was due to the ICT state. Photoluminescence (PL) spectra of compounds 7a and 7b in different

Aryl-substituted acridanes as hosts for TADF-based OLEDs

• Naveen Masimukku,
• Dalius Gudeika,
• Oleksandr Bezvikonnyi,
• Ihor Syvorotka,
• Rasa Keruckiene,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 989–1000, doi:10.3762/bjoc.16.88

• to polarity and aggregation effects. Despite these observations, emission of compounds 3–6 can mainly be assigned to π–π* transitions of local excited states. However, a slight contribution of charge transfer (CT) can be also recognized in the emission of the studied compounds 3–6 (Figure 3a). The

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

• chemical transformations come from this process, whose crucial step involves the formation of a charge-transfer complex between singlet oxygen and the amine. Subsequently, hydrogen-atom abstraction leads to the radical intermediate, which can undergo SET with a hydroperoxyl radical to afforded an iminium

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• extended π system or an intramolecular charge transfer (ICT). This property may allow to use visible light with longer wavelength to induce the ring-opening reaction, which would be favorable, e.g., for biological applications. The stilbene etheno bridge, however, may also lead to an intricate photochromic

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

• extinction coefficients and charge transfer states as well as relatively long-lived triplet states in solution, making them suitable as photoinitiators [36][37]. The irradiation and excitation of DEABP (27) to the singlet state is followed by intersystem crossing to the triplet state 29, which then leads to

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• -membered ring B. The large difference between the LUMO and HOMO leads to an intramolecular charge transfer, resulting in broad absorption bands in the UV–vis spectrum (Figure 3a) [36]. In addition, the LUMO energy of 1 (−2.98 eV) is significantly lower than that of 6 (−2.38 eV), which is responsible for

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

• could also play a role. For every lactone product that is formed, HCl is generated and in the case of fac-[Ir(ppy)3], the acid could potentially cause protodemetalation. This protodemetalation could be even more pronounced in the excited state (which is after all a metal-to-ligand charge-transfer 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

• seen in Figure 8, the mechanism of the reaction commences with the deprotonation of the biphenyl carboxylic acid 36, followed by the reaction of 38 with dimethyl dicarbonate (DMDC) to generate compound 39. On the other hand, the photocatalyst is excited by metal–ligand charge transfer, which produces

Synthesis, liquid crystalline behaviour and structure–property relationships of 1,3-bis(5-substituted-1,3,4-oxadiazol-2-yl)benzenes

• Afef Mabrouki,
• Malek Fouzai,
• Armand Soldera,
• Abdelkader Kriaa and
• Ahmed Hedhli

Beilstein J. Org. Chem. 2020, 16, 149–158, doi:10.3762/bjoc.16.17

• electron D–A concept may be regarded as Lewis base–Lewis acid type or charge-transfer. Based upon the above considerations, we could attribute the close proximity of fluorinated chains in conformation B to a throw space electron D–A intramolecular interaction between the perfluoroalkyl chains (electron

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

• , the strong donor–acceptor system in 3a led to an intramolecular charge-transfer (ICT) state that did not lead to a subsequent photoreaction [77]. In contrast, the absorption bands of the substrates 3b–d decreased relatively fast upon irradiation, but the maxima did not disappear completely (Figure 5B

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

• benzoquinone (BQ)-based charge-transfer (CT) derivatives in good yields. The optoelectronic properties of these compounds were explored both theoretically and experimentally and correlations to their structures were identified as a function of the nature and position of the donor group (meta and para) attached

• arylboronic acids are readily accessible, we envisaged that our Pd-catalyzed direct C–H functionalization method would be ideal for attempting a facile and direct route to a series of novel substituted benzoquinone-based charge-transfer derivatives, with the aim of exploring their electroluminescent (EL

• is difficult to realize highly efficient TADF emitters, which is especially the case for red emitters where nonradiative rates are high due to the well-known energy gap law [28]. While anthraquinone-based charge-transfer compounds have recently been shown to exhibit TADF that then translated to their

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

• Nadezhda S. Demina,
• Nikita A. Kazin,
• Nikolay A. Rasputin,
• Roman A. Irgashev and
• Gennady L. Rusinov

Beilstein J. Org. Chem. 2019, 15, 2678–2683, doi:10.3762/bjoc.15.261

• used to architect various ring-fused S-heteroacenes, which have been studied extensively [8][9][10] due to their better characteristics compared to heteroatom-free acenes. For instance, S-heteroacenes have a better oxidation stability due to lower-lying HOMO levels, as well as more efficient charge

• transfer because of their tendency to π-stack, with non-bonded sulfur–sulfur interactions in the solid state, which results in large intermolecular orbital coupling of HOMOs and, as a consequence, enhanced carrier transport properties [10]. However, there is a problem of poor solubility of a number of S

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

• noted in all tested solvents (134–173 nm), thus pointing to efficient stabilizations through intramolecular charge-transfer (ICT) processes from the excited states. The largest Stokes shift was noted in the aqueous solution, indicating the dye’s stability in this solvent. The solvatochromic analyses of

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

• , 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

• these dyes such as intramolecular charge-transfer processes and tunable red-shifted emission bands. Generally, the so far investigated borylated arylisoquinoline dyes show principally fluorescence quenching (on-off switching) on the formation of the corresponding fluoroboronate complexes [37]. Herein

• situated in between. These trends support that for the herein investigated dyes intramolecular charge-transfer (ICT) phenomena might play a role in the observation of the LW emission features. According to our previous observations the electron-acceptor moiety is likely constituted by the isoquinolinyl

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• films on a glass support was probed by the energy of the charge transfer transition in the oxazine dye Nile red (NR) at 25 °C. The absorption and fluorescence spectra of NR were observed to shift to the red with increasing solvent polarity, because of the intramolecular charge transfer character of the

• NR molecules in the ground state and slow sub-glass transition (Tg) relaxations in PMMA. Keywords: charge transfer; dipole moment; fluorescence; inhomogeneous broadening; oxazine dye; polarity probe; polymer permittivity; Introduction The chain and segment mobility as well as the permittivity of

• the phenomenon is still far from accurate. Fortunately, a contribution of solute to the large amplitude motion of the diethylamino group (twisting) in intramolecular charge transfer excited state of NR, postulated in references [21][24][25] was later associated with an artefact [26]. However, the

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the

• PSHD system was of interest to us as a potential photochromic photooxidant that would add an additional level of gating to photoinduced charge transfer (PICT) initiated processes (Figure 1). PSHDs were promising for this, as their photochromic reversion of LW back to SW proceeds purely thermally

• , and thus it makes sense that any thermal or solvatochromic LW is the eLW isomer. Conclusion While moving from PSHD (7) to QSHD (3) increased ΔEored between SW and pLW isomers, and therefore capacity to gate photoinduced charge transfer, by about 130 mV, the excited state reduction potential E*red of

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• isomerization occurs on a fast <1 ps timescale in both toluene and acetonitrile, while the excited state lifetime of the Z-form depends on solvent polarity, suggesting a partial charge transfer nature of its low lying excited state. Time-resolved luminescence measurements evidence the presence of a main

• solvent polarity. On the contrary, the excited state lifetime of the Z-isomer depends on the solvent properties and is especially short in MeOH, suggesting that the excited state of the molecule could have a partial charge transfer nature. Finally, transient absorption spectroscopy was employed as an

• further decreases in methanol. As shown in Supporting Information File 1 (Figure S3) the bleaching recovery of the not isomerized population fraction follows the same kinetics. The observed solvent dependence of the ESA decay could indicate that the excited state of the Z-form has a partial charge

Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

• Andrey G. Lvov,
• Max Mörtel,
• Anton V. Yadykov,
• Frank W. Heinemann,
• Valerii Z. Shirinian and
• Marat M. Khusniyarov

Beilstein J. Org. Chem. 2019, 15, 2428–2437, doi:10.3762/bjoc.15.235

• complex 8 shows a single major absorption band in the low energy UV region at 346 nm (ε = 6.22 × 104 M−1·cm−1), which appears bathochromically shifted compared to the free ligand. No charge transfer (CT) bands are visible in the spectrum. The low intensity broad shoulder, which spans almost the entire

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• intervalence charge transfer characteristics of the zwitterionic MV state. Keywords: anion binding; electrochemistry; hydrogen bonding; triarylamine; urea; zwitterionic mixed valency; Introduction Mixed-valence (MV) compounds have received increasing attention from the viewpoint of fundamental research on

• on evaluating the intervalence charge transfer (IVCT) transition near-infrared (NIR) absorption from NAr3 to NAr3•+ units [1][2][3][4][5]. The IVCT absorptions of MV compounds are generally more pronounced in organic species [19][20] than in their inorganic counterparts. The strong IVCT

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

• helped to increase the ability of complexation of 12 with iodide [56]. 2.7. Functional molecular crystal and materials Combining anion–arene interactions and controlling the electron-transfer or charge-transfer process concerning an anionic guest by using a cyclophane is uncommon [57] but can be realized

• between anions and the NDI motif [59]. NDI was chosen due to its excellent photochemical and electrochemical properties. In addition, the electron deficiency and aromatic nature of NDI is important for anion–π interactions [60] to control the charge-transfer properties. It also has been observed that in

• the solid state the movement of the molecules is restricted because of charge-transfer complexes between NDI and Cl−, Br− or I−. Because macrocycle 13 precipitated in less polar organic solvents upon addition of halides, the binding affinities were studied in DMSO in which the binding constants for Cl

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• rhodamines [43][44]. The weak tails on the red side of these bands are tentatively assigned to internal charge-transfer transitions from the perpendicularly [19][42] arranged ethylthio(dimethoxy)phenyl group to the xanthenium/acridinium systems polarized along the y-axes (Figure 4, inset). This

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• combinatorial chemistry. This highlight article discusses the unusual properties of fulvenes and their varied cycloaddition chemistry, focussing on applications in organic and natural synthesis, dynamic combinatorial chemistry and materials chemistry, including dynamers, hydrogels and charge transfer complexes

• the formation of several materials, including dynamic polymers (dynamers) [190], hydrogels [191], and precursors to charge-transfer complexes [181][234][235]. Dynamers, referred to as dynamers, are a class of adaptive polymers formed through reversible covalent bonds or noncovalent interactions

• fuelled advances in organic and natural product synthesis, dynamic combinatorial chemistry and materials science, including dynamers, hydrogels and charge transfer complexes. The recent advances show that potential applications for fulvene cycloaddition reactions are varied and wide in scope. We believe