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Search for "push–pull systems" in Full Text gives 7 result(s) in Beilstein Journal of Organic Chemistry.
Photoswitches beyond azobenzene: a beginner’s guide
- Michela Marcon,
- Christoph Haag and
- Burkhard König
Beilstein J. Org. Chem. 2025, 21, 1808–1853, doi:10.3762/bjoc.21.143
- photophysical properties. Push–pull systems, where a combination of an electron-donating group on one side of the azo bond (push) and an electron-withdrawing one on the other side (pull) decreases the double bond character of the N=N motif, are characterised by rotational thermal relaxation (Scheme 3) [16]. Due
Graphical Abstract
Figure 1: Energy diagram of a two-state photoswitch. Figure 1 was redrawn from [2].
Figure 2: Example of the absorption spectra of the isomers of a photoswitch with most efficient irradiation w...
Scheme 1: Photoswitch classes described in this review.
Figure 3: Azoheteroarenes.
Scheme 2: E–Z Isomerisation (top) and mechanisms of thermal Z–E isomerisation (bottom).
Scheme 3: Rotation mechanism favoured by the electron displacement in push–pull systems. Selected examples of...
Figure 4: A) T-shaped and twisted Z-isomers determine the thermal stability and the Z–E-PSS (selected example...
Figure 5: Effect of di-ortho-substitution on thermal half-life and PSS.
Figure 6: Selected thermal lifetimes of azoindoles in different solvents and concentrations. aConcentration o...
Figure 7: Aryliminopyrazoles: N-pyrazoles (top) and N-phenyl (bottom).
Scheme 4: Synthesis of symmetrical heteroarenes through oxidation (A), reduction (B), and the Bayer–Mills rea...
Scheme 5: Synthesis of diazonium salt (A); different strategies of azo-coupling: with a nucleophilic ring (B)...
Scheme 6: Synthesis of arylazothiazoles 25 (A) and heteroaryltriazoles 28 (B).
Scheme 7: Synthesis of heteroarylimines 31a,b [36-38].
Figure 8: Push–pull non-ionic azo dye developed by Velasco and co-workers [45].
Scheme 8: Azopyridine reported by Herges and co-workers [46].
Scheme 9: Photoinduced phase transitioning azobispyrazoles [47].
Figure 9: Diazocines.
Scheme 10: Isomers, conformers and enantiomers of diazocine.
Scheme 11: Partial overlap of the ππ* band with electron-donating substituents and effect on the PSS. Scheme 11 was ada...
Figure 10: Main properties of diazocines with different bridges. aMeasured in n-hexane [56]. bMeasured in THF. cMe...
Scheme 12: Synthesis of symmetric diazocines.
Scheme 13: Synthesis of asymmetric diazocines.
Scheme 14: Synthesis of O- and S-heterodiazocines.
Scheme 15: Synthesis of N-heterodiazocines.
Scheme 16: Puromycin diazocine photoswitch [60].
Figure 11: Indigoids.
Figure 12: The main representatives of the indigoid photoswitch class.
Scheme 17: Deactivation process that prevents Z-isomerisation of indigo.
Figure 13: Stable Z-indigo derivative synthesised by Wyman and Zenhäusern [67].
Figure 14: Selected examples of indigos with aliphatic and aromatic substituents [68]. Dashed box: proposed π–π in...
Scheme 18: Resonance structures of indigo and thioindigo involving the phenyl ring.
Scheme 19: Possible deactivation mechanism for 4,4'-dihydroxythioindigo [76].
Scheme 20: Effect of different heteroaryl rings on the stability and the photophysical properties of hemiindig...
Figure 15: Thermal half-lives of red-shifted hemithioindigos in toluene [79]. aMeasured in toluene-d8.
Scheme 21: Structures of pyrrole [81] and imidazole hemithioindigo [64].
Figure 16: Examples of fully substituted double bond hemithioindigo (left), oxidised hemithioindigos (centre),...
Scheme 22: Structure of iminothioindoxyl 72 (top) and acylated phenyliminoindolinone photoswitch 73 (bottom). ...
Scheme 23: (top) Transition states of iminothioindoxyl 72. The planar transition state is associated with a lo...
Scheme 24: Baeyer–Drewsen synthesis of indigo (top) and N-functionalisation strategies (bottom).
Scheme 25: Synthesis of hemiindigo.
Scheme 26: Synthesis of hemithioindigo and iminothioindoxyl.
Scheme 27: Synthesis of double-bond-substituted hemithioindigos.
Scheme 28: Synthesis of phenyliminoindolinone.
Scheme 29: Hemithioindigo molecular motor [85].
Figure 17: Arylhydrazones.
Scheme 30: Switching of arylhydrazones. Note: The definitions of stator and rotor are arbitrary.
Scheme 31: Photo- and acidochromism of pyridine-based phenylhydrazones.
Scheme 32: A) E–Z thermal inversion of a thermally stable push–pull hydrazone [109]. B) Rotation mechanism favoured...
Scheme 33: Effect of planarisation on the half-life.
Scheme 34: The longest thermally stable hydrazone switches reported so far (left). Modulation of thermal half-...
Figure 18: Dependency of t1/2 on concentration and hypothesised aggregation-induced isomerisation.
Figure 19: Structure–property relationship of acylhydrazones.
Scheme 35: Synthesis of arylhydrazones.
Scheme 36: Synthesis of acylhydrazones.
Scheme 37: Photoswitchable fluorophore by Aprahamian et al. [115].
Scheme 38: The four-state photoswitch synthesised by the Cigáň group [116].
Figure 20: Diarylethenes.
Scheme 39: Isomerisation and oxidation pathway of E-stilbene to phenanthrene.
Scheme 40: Strategies adapted to avoid E–Z isomerisation and oxidation.
Scheme 41: Molecular orbitals and mechanism of electrocyclisation for a 6π system.
Figure 21: Aromatic stabilisation energy correlated with the thermal stability of the diarylethenes [127,129].
Figure 22: Half-lives of diarylethenes with increasing electron-withdrawing groups [128,129].
Scheme 42: Photochemical degradation pathway promoted by electron-donating groups [130].
Figure 23: The diarylethenes studied by Hanazawa et al. [134]. Increased rigidity leads to bathochromic shift.
Scheme 43: The dithienylethene synthesised by Nakatani's group [135].
Scheme 44: Synthesis of perfluoroalkylated diarylethenes.
Scheme 45: Synthesis of 139 and 142 via McMurry coupling.
Scheme 46: Synthesis of symmetrical derivatives 145 via Suzuki–Miyaura coupling.
Scheme 47: Synthesis of acyclic 148, malonic anhydride 149, and maleimide derivatives 154.
Figure 24: Gramicidin S (top left) and two of the modified diarylethene derivatives: first generation (bottom ...
Scheme 48: Pyridoxal 5'-phosphate and its reaction with an amino acid (top). The analogous dithienylethene der...
Figure 25: Fulgides.
Scheme 49: The three isomers of fulgides.
Scheme 50: Thermal and photochemical side products of unsubstituted fulgide [150].
Figure 26: Maximum absorption λc of the closed isomer compared with the nature of the aromatic ring and the su...
Scheme 51: Possible rearrangement of the excited state of 5-dimethylaminoindolylfulgide [153].
Figure 27: Quantum yields of ring closure (ΦE→C) and E–Z isomerisation (ΦE→Z) correlated with the increasing s...
Scheme 52: Active (Eα) and inactive (Eβ) conformers (left) and the bicyclic sterically blocked fulgide 169 (ri...
Scheme 53: Quantum yield of ring-opening (ΦC→E) and E–Z isomerisation (ΦE→Z) for different substitution patter...
Scheme 54: Stobbe condensation pathway for the synthesis of fulgides 179, fulgimides 181 and fulgenates 178.
Scheme 55: Alternative synthesis of fulgides through Pd-catalysed carbonylation.
Scheme 56: Optimised synthesis of fulgimides [166].
Scheme 57: Photoswitchable FRET with a fulgimide photoswitch [167].
Scheme 58: Three-state fulgimide strategy by Slanina's group.
Figure 28: Spiropyrans.
Scheme 59: Photochemical (left) and thermal (right) ring-opening mechanisms for an exemplary spiropyran with a...
Figure 29: Eight possible isomers of the open merocyanine according to the E/Z configurations of the bonds hig...
Scheme 60: pH-Controlled photoisomerisation between the closed spiropyran 191-SP and the open E-merocyanine 19...
Scheme 61: Behaviour of spiropyran in water buffer according to Andréasson and co-workers [180]. 192-SP in an aqueo...
Scheme 62: (left box) Proposed mechanism of basic hydrolysis of MC [184]. (right box) Introduction of electron-dona...
Scheme 63: Photochemical interconversion of naphthopyran 194 (top) and spirooxazine 195 (bottom) photoswitches...
Scheme 64: Synthesis of spiropyrans and spirooxazines 198 and the dicondensation by-product 199.
Scheme 65: Alternative synthesis of spiropyrans and spirooxazines with indolenylium salt 200.
Scheme 66: Synthesis of 4’-substituted spiropyrans 203 by condensation of an acylated methylene indoline 201 w...
Scheme 67: Synthesis of spironaphthopyrans 210 by acid-catalysed condensation of naphthols and diarylpropargyl...
Scheme 68: Photoswitchable surface wettability [194].
Figure 30: Some guiding principles for the choice of the most suitable photoswitch. Note that this guide is ve...
Substituent effects in N-acetylated phenylazopyrazole photoswitches
- Radek Tovtik,
- Dennis Marzin,
- Pia Weigel,
- Stefano Crespi and
- Nadja A. Simeth
Beilstein J. Org. Chem. 2025, 21, 830–838, doi:10.3762/bjoc.21.66
- relative position of the absorption bands in the azobenzene derivatives depends on the substitution pattern on the aromatic rings, which can act as a handle to affect the absorption properties of the compound class [3]. For instance, push–pull systems or the introduction of tetra-ortho substituents were
Graphical Abstract
Scheme 1: Reaction pathway for synthesizing NH-substituted, methylated-, and acetylated arylazopyrazoles. Con...
Figure 1: UV–vis absorption spectra of selected NAc-PAP derivatives in CH3CN. The strong π→π* can be observed...
Figure 2: A) Time-resolved UV–vis absorption spectra of NAc-PAP-CN upon 365 nm irradiation (12.5 µM in CH3CN,...
Figure 3: Hammett plot of NAc-PAP derivatives.
Figure 4: Eyring plots for NAc-PAP-CN and NAc-PAP-OMe.
Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines
- Andrejs Šišuļins,
- Jonas Bucevičius,
- Yu-Ting Tseng,
- Irina Novosjolova,
- Kaspars Traskovskis,
- Ērika Bizdēna,
- Huan-Tsung Chang,
- Sigitas Tumkevičius and
- Māris Turks
Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41
- transformed into the title compounds by CuAAC reaction. The designed compounds belong to the push–pull systems and possess promising fluorescence properties with quantum yields in the range from 28% to 60% in acetonitrile solution. Due to electron-withdrawing properties of purine and 7-deazapurine
- to increased fluorescence quantum yield (74%) in THF solution. The compounds exhibit low cytotoxicity and as such are useful for the cell labelling studies in the future. Keywords: 7-deazapurines; fluorescence; nucleophilic aromatic substitution; purines; push–pull systems; pyrrolo[2,3-d]pyrimidines
- ; Introduction Purine [1][2][3][4][5][6][7] and 7-deazapurine (IUPAC name: pyrrolo[2,3-d]pyrimidine) [8][9][10][11] derivatives have been progressively studied for decades due to their wide range of biological activities and photophysical properties. Currently, the synthesis of push–pull systems is a promising
Graphical Abstract
Figure 1: Examples of fluorescent purine/7-deazapurine derivatives.
Scheme 1: General synthetic routes for the compounds 5, 7–9, 10 and 11. Method A: alkyl halogenide, MeCN or D...
Figure 2: 1H NMR spectra of compound 6b in CD3CN at different temperatures (300 MHz, c = 12.5 mg/mL); a, b, c...
Figure 3: Comparison of 1H NMR spectra of compounds 8a and 5 (300 MHz, CDCl3).
Figure 4: a) Experimental UV–vis absorption spectra (lines) with computed theoretical absorption bands (colum...
Figure 5: Photos of compound 8c (A and B) and compound 11c (C and D) in THF, CHCl3, DMSO, MeCN and MeOH befor...
Figure 6: a) Fluorescence spectra of compounds 8c (λexc = 360 nm) and 11c (λexc = 370 nm) in solvents of diff...
Figure 7: Energy diagram for the frontier molecular orbitals of compounds 8a, 8c, 11a and 11c.
Figure 8: Labeled MCF-7 cells using compound 9 (C,D) and unlabeled MCF-7 cells (A,B) in microscope (2 h, c(9)...
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
- particular, the electrophilic enyne intermediate [32][40], which is trespassed in the three-component synthesis of solid-state luminescent push–pull indolones 4, intrigued our interest for accessing even triene push–pull systems and to study their electronic properties. Here we report our findings on the
Graphical Abstract
Figure 1: Linear push–pull solid-state diene lumophores with conformationally flexible and fixed acceptor moi...
Scheme 1: Three-component synthesis of 1-styryleth-2-enylideneindolones 8.
Figure 2: DFT-computed energy differences of the stereoisomers of 2Z,4Z-8a and 2Z,4E-8a.
Scheme 2: Three-component synthesis of 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones 10.
Figure 3: DFT-computed energy differences of the stereoisomers of 10a and 10h.
Scheme 3: Mechanistic rationale of the three-component sequence furnishing the 1-styryleth-2-enylideneindolon...
Figure 4: DFT-computed (B3LYP functional, 6-31G* basis set) HOMO (left) and LUMO (right) of merocyanine 8a.
Figure 5: Absorption and emission spectrum of the dropcasted film of compound 8a (recorded at room temperatur...
Figure 6: Absorption spectrum of the dropcasted film of compound 10d (recorded at room temperature, normalize...
Figure 7: Absorption spectra of compound 10h in dichloromethane (right trace) and of the dropcasted film (lef...
Figure 8: DFT-computed (B3LYP functional, 6-311G(d,p) basis set) FMOs (HOMO, bottom; LUMO (center), and LUMO+...
Recent advances towards azobenzene-based light-driven real-time information-transmitting materials
- Jaume García-Amorós and
- Dolores Velasco
Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113
- and 1.3 ms in ethanol, respectively, which decrease further down to 1.1 ms and 644 µs in the presence of phenol (Figure 23). This demonstrates that the generation of push–pull systems by the establishment of hydrogen bonds between phenol groups and the pyridinic nitrogen, with the subsequent
Graphical Abstract
Figure 1: Some important families of photochromic compounds and their photochromic reactions.
Figure 2: Photochromism of azobenzene derivatives and energetic profile for the switching process.
Figure 3: General overview of the different types of azoderivatives presented in this review.
Figure 4: Changes in the electronic spectrum of a 3 cis-to-trans isomerising ethanol solution at 45 °C (Δt = ...
Figure 5: Chemical structure and thermal relaxation time in ethanol at 298 K, τ, for the slow thermally-isome...
Figure 6: Rotation and inversion mechanisms proposed for the thermal cis-to-trans isomerisation processes of ...
Figure 7: Effect of the presence of the electron-withdrawing cyano and nitro groups on the thermal relaxation...
Figure 8: Transient absorption generated by UV irradiation (λ = 355 nm) for azo-dyes 8 (right) and 9 (left) i...
Figure 9: Effect of the presence of a positively charged nitrogen as an electron-withdrawing group on the the...
Figure 10: Mechanism proposed for the thermal cis-to-trans isomerisation process for the push–pull azopyridini...
Figure 11: Comparison between the thermal relaxation time at 298 K, τ, for the azoderivative 4 (type-I) and th...
Figure 12: Solvent effect on the thermal relaxation time at 298 K, τ, for the type-II azophenols 11–13.
Figure 13: Transient generated by irradiation with UV-light (λ = 355 nm) for the type-II azophenol 12 in ethan...
Figure 14: Proposed isomerisation mechanisms for the thermal cis-to-trans isomerisation of the alkoxy-substitu...
Figure 15: Solvent effect on the thermal relaxation time at 298 K, τ, for the type-II ortho-substituted azophe...
Figure 16: Cooperative effect of the para- and ortho-hydroxyl groups in azophenol 17.
Figure 17: Effect of the poly-hydroxylation of the azobenzene core on the thermal relaxation time at 298 K, τ,...
Figure 18: Transients generated by irradiation with UV-light (λ = 355 nm) for the poly-substituted azophenol 18...
Figure 19: Effect of the introduction of electron-withdrawing groups in the position 4’ of the azophenol struc...
Figure 20: Transient absorptions generated by UV irradiation (λ = 355 nm) of azo-dyes 11 (type-II), 19 (type-I...
Figure 21: Effect of the introduction of the hydroxyl group in the position 2’ of the push–pull azo-dye on the...
Figure 22: Effect of the substitution of a benzene ring by a pyridine one on the thermal relaxation time in et...
Figure 23: Influence of the introduction of additional electron-withdrawing nitro groups in the pyridine ring ...
Figure 24: Chemical structure and thermal relaxation time in ethanol at 298 K, τ, for the type-III azoderivati...
Figure 25: Oscillation of the optical density of an ethanol solution of azo-dye 26 generated by UV-light irrad...
Imidazole as a parent π-conjugated backbone in charge-transfer chromophores
- Jiří Kulhánek and
- Filip Bureš
Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4
- Jiri Kulhanek Filip Bures Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice, CZ-53210, Czech Republic 10.3762/bjoc.8.4 Abstract Research activities in the field of imidazole-derived push–pull systems featuring
- made in the development and the investigation of new organic push–pull systems. In contrast to inorganic materials, the advent of dipolar (hetero)organic materials with readily polarizable structure was stimulated by their relative ease of synthesis, well-defined structure, chemical and thermal
- electronic behavior of the appended donors and acceptors and the character and length of the π-conjugated linker [4][5][6][7]. Recently, it was also recognized that push–pull systems applicable as organic materials should possess high chemical and thermal robustness, good solubility in common organic
Graphical Abstract
Figure 1: Schematic representation of organic D-π-A system featuring ICT.
Figure 2: Two principal orientations of the imidazole-derived charge-transfer chromophores.
Scheme 1: Common synthetic approach to triarylimidazole-, diimidazole-, and benzimidazole-derived CT chromoph...
Scheme 2: Syntheses of important 4,5-dicyanoimidazole derivatives 1–3 [27-30].
Figure 3: Donor–acceptor triaryl push–pull azoles 4a–h [31,32].
Figure 4: Y-shaped CT chromophores with an extended π-conjugated pathway and various donor and acceptor subst...
Figure 5: Molecular structures of chromophores 9–14 [13,15,37-41].
Figure 6: General structure of 4,5-bis(4-aminophenyl)imidazole-derived chromophores 15a–g with various π-link...
Figure 7: Various orientations of the substituents on the parent lophine π-conjugated backbone (16–19) and th...
Figure 8: Structure and electronic absorption spectra of chromophores 21–26 [12].
Figure 9: Typical D-π-A diimidazole CT chromophore [16-18,50-53].
Figure 10: Typical D-π-D diimidazoles 28–31 [19,54-56] and photochromic diimidazoles 32,33 [57,58].
Scheme 3: Oxidation of 1H-diimidazoles to 2H-diimidazoles (quinoids).
Figure 11: Typical benzimidazoles-derived D-π-A push–pull systems 35–43 [25,62-66].
Figure 12: Structure of benzimidazoles (44–47), imidazophenanthrolines (48–57), imidazophenanthrenes (58–60), ...
Scheme 4: Acidoswitchable NLO-phores 64,65 and ESIPT mechanism [72-74].
Figure 13: General structures of bis(benzimidazole) chromophores 67–71 and pyridinium betaines 72 [75-79].
Figure 14: Overview of 4,5-dicyanoimidazole derivatives investigated by Rasmussen et al. [29,81-94].
Figure 15: 4,5-Dicyanoimidazole-derived chromophores 84–87 [103-106].
Figure 16: Push–pull chromophores 88–93 with systematically extended π-linker [30].
Figure 17: pH-triggered NLO switches 88c–93c [109].
Figure 18: Dibromoolefin 94 and branched chromophores 95–100 [112,113].
Figure 19: Imidazole as a donor–acceptor unit in CT-chromophores 101–111 [20].
Figure 20: Diimidazoles 112–115 used as small electron acceptors in organic solar cells [115,116].
Figure 21: Amino- and hydroxy-functionalized chromophores incorporated into a polymer backbone Rpol [18,50-53,122-124].
Figure 22: Structure of polyphosphazene polymers bearing NLO-phores [125-127] and some other recent examples of nonline...
Figure 23: Epoxy- and silica-based polymers functionalized with 4,5-dicyanoimidazole unit [105,130].
Convenient methods for preparing π-conjugated linkers as building blocks for modular chemistry
- Jiří Kulhánek,
- Filip Bureš and
- Miroslav Ludwig
Beilstein J. Org. Chem. 2009, 5, No. 11, doi:10.3762/bjoc.5.11
- most important goals of modern material chemistry. Organic chemists steadily attempt to design and synthesize novel and well-defined organic push-pull systems with prospective applications as chromophores for nonlinear optics (NLO) [1][2][3][4][5], dyes [6], electronic and photonic devices [7][8
- formation of the target molecule [19][20] or a separate preparation of the donor as well as the acceptor moieties and their final combination [21][22]. It is already well known that the HOMO/LUMO gap and polarizability of the push-pull systems with the given donors and acceptors can be finely tailored by
Graphical Abstract
Figure 1: Basic and newly proposed π-conjugated linkers designed for the Suzuki–Miyaura and Sonogashira cross...
Scheme 1: Convenient synthetic methods leading to π-linkers 3–6.
Scheme 2: Sonogashira cross-coupling leading to π-linkers 7c–9c.
