Photophysical, photostability, and ROS generation properties of new trifluoromethylated quinoline-phenol Schiff bases

• Inaiá O. Rocha,
• Yuri G. Kappenberg,
• Wilian C. Rosa,
• Clarissa P. Frizzo,
• Nilo Zanatta,
• Marcos A. P. Martins,
• Isadora Tisoco,
• Bernardo A. Iglesias and
• Helio G. Bonacorso

Beilstein J. Org. Chem. 2021, 17, 2799–2811, doi:10.3762/bjoc.17.191

• the 400–550 nm region depending on the solvent polarity (CHCl3, DMSO, and MeOH). Therefore, it is possible to infer that the polarity of the solvents directly influences the electronic transitions in the excited state, with significant changes for the compound in more polar and protic solvents, by

• = Ph, R1 = 4-NO2) were analyzed, a significant difference was observed compared to the other compounds in the series 3. Thus, we can say that these characteristics exist because there is more stabilization of the excited state in a polar environment (DMSO and MeOH), adding to a possible push–pull

• effect of the diethylamino group (donor group) [14][28][29]. Moreover, these results should indicate a negative possibility of excited state intramolecular proton transfer (ESIPT) phenomena occurring (in protic MeOH solvent and low values of Stokes shifts), being only a direct influence of the

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• ; however, they suffer from relatively poor photostability [14][15][16]. Transition-metal-photoredox catalysts, such as ruthenium and iridium polypyridyl complexes, exhibit high redox potentials, long excited state lifetimes, and strong absorption [17][18][19][20]. However, high cost and their scarcity

• oxidized RuIII, which subsequently accepts an electron from an external donor (D) to form the ground-state catalyst RuII. This type of reaction mechanism is an oxidative quenching cycle (OQC). Alternatively, the lower energy SOMO of the excited state RuII* can accept an electron from an external donor

• , which is referred to as a reductive quenching cycle (RQC; Scheme 1). Compared with the photoredox mechanism of ruthenium-based catalysts, copper complexes show unique features [22][28]. Under irradiation, the copper complex CuI is converted to the excited state CuI*, which transfers electrons to an

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• through oxidative quenching of the excited substrate. While an excited state of 1 could react in a similar fashion, the absorption maximum of 1 is centered around 280 nm, which is outside the emission spectrum of green LEDs. A recent study by Hashmi et al. [44], however, shed a completely different light

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• ) resulting in a relatively small electron repulsion energy in the first singlet excited state and thus, a small HOMO–LUMO (S0–S1) gap compared to naphthalene. The large energy gap between its S2 and S1 states (up to 15000 cm−1) makes internal conversion less probable, making azulene emit from the S2 state

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Synthesis of 10-O-aryl-substituted berberine derivatives by Chan–Evans–Lam coupling and investigation of their DNA-binding properties

• Peter Jonas Wickhorst,
• Mathilda Blachnik,
• Denisa Lagumdzija and
• Heiko Ihmels

Beilstein J. Org. Chem. 2021, 17, 991–1000, doi:10.3762/bjoc.17.81

• low fluorescence quantum yields are caused by conformational changes in the excited state, the fluorescence was recorded in media with different viscosity, namely in glycerol at different temperatures (Figure 2, Figure S2, Supporting Information File 1). It was observed that the derivatives 5a–e have

• deactivation of the excited state by conformational changes, e.g., torsional relaxation [42][43]. Since the fluorescence quantum yield of the parent berberine (1a) does not correlate well with the viscosity of the medium [40], it was concluded that the weak light-up effect in glycerol is mainly caused by the

• suppressed rotation about the Ar–O bond. Nevertheless, as the emission quantum yield of the derivatives 5a–e still remained low, even at high viscosity of the medium, there obviously exist additional relaxation pathways in the excited state, most likely a photo-induced electron transfer (PET) from the 10

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• the excited state, causing an electron transfer to give radicals and to initiate subsequent reactions. Besides light as an external energy source, reactions involving the participation of EDA complexes are mild, obviating transition metal catalysts or photosensitizers in the majority of cases and are

• the fact that diamine can condense with the enol substrate, forming an imine-ion intermediate absorbing in the visible region. The direct excitation of the intermediate leads to a charge-transfer excited state, completing the stereocontrolled intermolecular cycloaddition reaction with a good ratio of

• enantiomer to diastereomer. A plausible mechanism is shown in Scheme 19. In the presence of acid, EDA complex 52 is formed by ketene 48 and diamine 51. Then, the ground state 52 transforms into excited state 53 or into unproductive charge-transfer excited state 54 that can restore ground state 52 by BET

Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• strong blue shift, observed in methanol and water solution. So, in the ground state, the N5 atom of 8a has a large negative charge (Figure 5) and strongly interacts with polar solvents. Therefore, polar solvents significantly decrease the ground state energy. When the excited state emerges, the strong CT

• from the =N5–H group to the tetrazole ring (Figure 6c and d) leads to a decrease in the electronic density on the N5 atom. The solvent molecules do not have time to rearrange in order to stabilize the excited state. This results in a lower ground state energy, but not the excited state. Therefore, the

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

• Dongyang Chen and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 210–223, doi:10.3762/bjoc.17.21

• phase [30][31]. The lowest energy structures from these DFT calculations were used as input geometries for excited-state calculations using the Tamm–Dancoff approximation (TDA) to TD-DFT, which provide computed energies of the excited singlet and triplet states [32][33]. The nature of the lowest singlet

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to

• molecules in aqueous solution. The building blocks pelargonidin chloride (Flavy), 1-naphthol-3,6-disulfonate (1N36S), and poly(allylamine) are depicted in Scheme 2. The aim was to exploit the photoacid's unique capability to undergo photoinduced intermolecular excited state proton transfer reactions, both

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• system. Based on the above-mentioned approaches, organic and inorganic template-assisted diverse supramolecular assemblies have been constructed to optimize the photochemical reactivity as well as regio- and enantioselectivity [5][6]. In addition, to understand the excited-state properties of the guest

• photochemical reactions, including photoisomerization, photocyclodimerization, and H2 evolution [7][23]. Chirality induction in a prochiral guest via photochemical reactions is a delightful approach. This can not only transfer the chirality of the host cavity to the molecular photoproduct via excited-state

• occupancy 95%) in MeOH/H2O solutions (0.25:0.75, 0.5:0.5, and 0:1, respectively). This may be due to fact that the CD-functionalized sensitizing group could increase the product yield through excited-state supramolecular interactions within the cavity. In addition, the spacer attached to the primary hydroxy

Circularly polarized luminescent systems fabricated by Tröger's base derivatives through two different strategies

• Cheng Qian,
• Yuan Chen,
• Qian Zhao,
• Ming Cheng,
• Chen Lin,
• Juli Jiang and
• Leyong Wang

Beilstein J. Org. Chem. 2021, 17, 52–57, doi:10.3762/bjoc.17.6

• centers make it and its derivatives useful building blocks to construct CPL-active materials and to develop chiral phosphorescent materials in future. Ground-state and excited-state chirality of R2N-TBPP and S2N-TBPP. (a) CD spectra of R2N-TBPP and S2N-TBPP. (b) CPL spectra of R2N-TBPP and S2N-TBPP

Control over size, shape, and photonics of self-assembled organic nanocrystals

• Chen Shahar,
• Yaron Tidhar,
• Yunmin Jung,
• Haim Weissman,
• Sidney R. Cohen,
• Ronit Bitton,
• Iddo Pinkas,
• Gilad Haran and
• Boris Rybtchinski

Beilstein J. Org. Chem. 2021, 17, 42–51, doi:10.3762/bjoc.17.5

• excited state dynamics of the nanocrystals. Femtosecond transient absorption spectra of all assemblies displayed typical PDI excited state absorption peaks in the range of 600–770 nm [50], matching PDI bleaching represented by negative features at 550–600 nm. In the disaggregated state, almost no power

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• results and of the reported literature [58][61], to the singlet monomeric excited state and to the exciplex, respectively. While aryl phosphates have been only sparsely used as substrates in thermal cross-coupling reactions [65][66][67], their photochemical behavior has been the subject of various

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• environment responsiveness is based on having variable substituents at the para-position of the two phenyl moieties. The excited state properties were fully investigated in tetrahydrofuran (THF) solutions and in THF/H2O mixtures. The size of the aggregates in aqueous media were measured by dynamic light

• , the π-donor nature of the substituents on the phenyl ring constitutes the main parameter that influences the photophysical properties, such as excited state lifetimes and photoluminescence quantum yields. Hence, a series of highly luminescent materials from deep blue to red emission depending on

• ) character (n–π*) of the excited state. Due to sterical hindrance, the two adjacent phenyl rotors restrict their molecular rotation in solution. The increasing push–pull (D–A) character progressively enhances the coupling with solvent molecules and sensitivity to changes in the dielectric constant when going

UV resonance Raman spectroscopy of the supramolecular ligand guanidiniocarbonyl indole (GCI) with 244 nm laser excitation

• Tim Holtum,
• Vikas Kumar,
• Daniel Sebena,
• Jens Voskuhl and
• Sebastian Schlücker

Beilstein J. Org. Chem. 2020, 16, 2911–2919, doi:10.3762/bjoc.16.240

• to conformational changes and/or increased transition polarizabilities due to minor changes of the ground and excited state potential. The difference spectrum (Figure 8, middle) shows strong peaks at 1033 cm−1, 1120 cm−1, 1225 cm−1, 1310 cm−1, 1355 cm−1, 1405 cm−1, 1450 cm−1, 1501 cm−1, 1616 cm−1

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• , cyclodextrins or micelles [55][56][57][58]. Presumably the radiationless deactivation of the excited state by conformational changes, that leads to the low emission intensity in aqueous solution, is suppressed in the sterically restricted binding site. Therefore, it can be deduced that the increased emission of

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• photocatalysts (PCs) generate excited state substrates that can then undergo reactions that would be impossible in the ground state [4]. A challenge for enantioselective catalysis is stifling the racemic background reaction, which is generally achieved through a lower activation energy for the catalysed process

• photocatalysts used for this reaction, it is proposed the excited state of 9 is sufficiently reducing to initiate the chain mechanism through an oxidative quench. Moving away from electronically activated halides, MacMillan et al. investigated a tricatalytic system, utilising enamine, photoredox, and HAT

• on their observation of similar reactivity when using bromomalonates 42 as substrates (direct excitation route) [35]. As no aryl ring is present, no EDA complex is formed, and thus direct excitation of the photoactive enamine intermediate affords an excited state enamine 41* that can reduce 42 to

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

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