Rotaxanes with integrated photoswitches: design principles, functional behavior, and emerging applications

• Jullyane Emi Matsushima,
• Khushbu,
• Zuliah Abdulsalam,
• Udyogi Navodya Kulathilaka Conthagamage and
• Víctor García-López

Beilstein J. Org. Chem. 2025, 21, 2345–2366, doi:10.3762/bjoc.21.179

• of the C–O bond “opens” the molecule, generating the corresponding merocyanine (Figure 2). The reverse photocyclization can occur upon exposure to visible light. Remarkably, the two isomers differ in their chemical and physical properties such as polarity, molecular volume, dipole moment

• the naphthalimide. Specifically, red fluorescence was observed when the merocyanine formed, and green fluorescence when the spiropyran was generated. Notably, this rotaxane was employed for the detection of sulfite, where the addition of sulfite led to the deactivation of FRET. This occurs due to a

• Michael addition taking place at the active site (C=C−C=N+) in the merocyanine unit in the presence of sulfite ions, resulting in color changes from red to green. This work represents a substantial advancement in the development of rotaxane-based fluorescent probes, providing highly sensitive and

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

Synthesis of photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline group

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Irina V. Dubonosova,
• Olga Yu. Karlutova,
• Oleg P. Demidov,
• Alexander D. Dubonosov and
• Vladimir A. Bren

Beilstein J. Org. Chem. 2024, 20, 552–560, doi:10.3762/bjoc.20.47

• inverse photochromism), such as merocyanine forms of spiropyrans and spirooxazines, azomethine imines, thioindigoid dyes and N→O acylotropic systems [12][13][14][15]. Recently, they have been actively used to create next-generation molecular switches, materials with new properties (in particular, color

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• involved in the main indigo chromophore comprising a C=C double bond substituted by two acceptors and two donor groups (Figure 4) [18]. Notably, the benzene rings make just a small contribution to the chromophore. In other words, the primary chromophore of indigo consists of two intersecting merocyanine

Selected peptide-based fluorescent probes for biological applications

• Debabrata Maity

Beilstein J. Org. Chem. 2020, 16, 2971–2982, doi:10.3762/bjoc.16.247

• nonfluorescent and colored ring-opened merocyanine (MCH+), fluorescent and colored ring-opened merocyanine (MC) and nonfluorescent and colorless ring-closed SP forms. Tian et al. in collaboration with the Schmuck group developed a bis-SP functionalized peptide 14 for pH monitoring in lysosomes and subsequent

• after incubation with the PDA liposomes. Reprinted with permission from [59]. Copyright (2011) American Chemical Society. a) Molecular structure of peptide 14; b) the coordinate represents the states of sensor at different pH values, purple sphere: protonated merocyanine (McH+), red sphere: normal

• merocyanine (Mc), and gray sphere: spiropyran at a ring-closed state (Sp); colocalization experiments using peptide 14, LysoTracker Green DND-26 (LTG) and Hoechst 33258 in A549 cells. Cells were stained with c) 10 µM peptide 14 (channel 1: excitation: 515 nm, emission collected: 600–650 nm), d) 0.1 µM LTG

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

• merocyanine formation, and the irradiation with light mainly led to photodegradation of the substrates. However, it was shown by colorimetric and fluorimetric screening assays as well as by detailed NMR spectroscopic and mass spectrometric studies that the addition of particular metal ions (Cu2+, Fe3+, and to

• photoreaction [12][15][16]. The photochromism is based on a reversible electrocyclic reaction that proceeds through the UV light-induced cleavage of the C2’–O bond of the closed, colorless form to give the colored, metastable merocyanine form, whereas the back reaction can be initiated thermally or by the

• irradiation with visible light, as is exemplarily shown for the spiroindolinonaphthoxazine 1a (Scheme 1) [15]. The merocyanine form 1aMC essentially possesses a planar structure, and because of the extended π system, the absorption maximum is significantly red-shifted in comparison to the closed form (e.g

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

• Alexis Perry and
• Christina J. Kousseff

Beilstein J. Org. Chem. 2017, 13, 1542–1550, doi:10.3762/bjoc.13.154

• for binding divalent metal cations and a modest increase in M2+ binding affinity correlated with increased alkycarboxylate tether length. Keywords: carboxylate ligand; merocyanine; metal binding; photochromism; spiropyran; Introduction Spiropyrans are a class of spiro-fused indolochromene (e.g

• ., C4SP, Scheme 1) which exist in photo-controlled equilibrium with their zwitterionic, fully-conjugated merocyanine isomer [1] (e.g., C4MC, Scheme 1). The controllable nature of this isomerisation and the dramatic differences in physical and chemical properties displayed by the isomeric forms, coupled

• with the facile elaboration of the spiropyran core, have made spiropyran–merocyanine systems a common motif in molecular switch and sensing applications [2]. In this respect, the difference in optical properties between colourless, non-fluorescent spiropyran and coloured, fluorescent merocyanine has

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

• ]quinolizinium was synthesized by cyclodehydration route and its optical properties in different media were investigated. The absorption and emission spectra of this compound depend on the pH of the solution. Thus, at higher pH values the deprotonation yields a merocyanine-type dye that exhibits significantly

• in a merocyanine-type conjugation (Scheme 2). A similar effect was postulated for the structurally resembling hydroxystyrylquinolizinium derivatives, such as 6 (Figure 8), that also show a red shift of the absorption upon deprotonation, although to a larger extent (from 405 to 472 nm) [50][51][52

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

• are slightly red-shifted and appear between 519 and 532 nm as a result of a J-aggregation [45]. Apparently, the aryl substitution on the triene moiety only affects the absorption bands to a minor extent. The merocyanine character of the 1-styryleth-2-enylideneindolones 8 is additionally supported by

• -aggregation the absorption bands of the films are red-shifted and appear between 599 and 623 nm (Table 4, Figure 6). The benzothiazol-terminated merocyanine 10h displays in dichloromethane solution a hypsochromically shifted absorption band at 563 nm with the highest molar extinction coefficient (Table 4

• , entry 13), yet for the amorphous film the most pronounced bathochromic shift in the series of the merocyanines 10 (Figure 7). In the solid state a merocyanine characteristic metallic green luster can be seen. Again, the aryl substitution on the triene moiety only affects the absorption bands to a minor

Diarylethene-modified nucleotides for switching optical properties in DNA

• Sebastian Barrois and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2012, 8, 905–914, doi:10.3762/bjoc.8.103

• only is a structural change observed but a large change in polarity is yielded additionally [10][22]. It is expected that the ring-closed spiropyran form of this molecular switch does not insert into the base stack due to its twisted structure, but the open merocyanine form could intercalate based on

• its planarity and polarity. This assumption was experimentally verified by synthetic spiropyrans as noncovalent DNA and RNA binders [23][24][25]. As expected, ground-state interactions between the noncovalently bound molecular switch and the DNA bases were detected in the case of the merocyanine form

A perfluorocyclopentene based diarylethene bearing two terpyridine moieties – synthesis, photochemical properties and influence of transition metal ions

• Falk Wehmeier and
• Jochen Mattay

Beilstein J. Org. Chem. 2010, 6, No. 53, doi:10.3762/bjoc.6.53

• processes between the ruthenium nuclei. On the other hand the closed isomer 10aC might act as an acceptor; a similar effect has been observed with a spiropyran moiety bridging two terpyridine units, whose (closed) merocyanine form inhibits the energy transfer between metal centres and thus acts as a T

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• (closed forms), also referred to as chromenes, leads to the formation of interconverting photoisomers of the open merocyanine-type (quinoidal, zwitterionic and hybrid forms and their stereoisomers), depending upon the substitution pattern of the parent pyrans and the conditions employed (Scheme 1

• ). Typically the thermal reversion of the open forms is very fast [17][18][19][20]. Quite recently, the formation of allene intermediates at low temperatures was also reported in the literature. They originate from open merocyanine isomers and are formed via a 1,5-hydrogen shift reaction [21][22]. However

• generates a flexible C3–C4 single bond within the open merocyanine forms in place of the former double bond of the pyran ring (Scheme 1), resulting in a significant structural alteration of the β-turn scaffold. Herein we describe the synthesis of functionalized photochromic pyrans by palladium-catalyzed