Photoreversible Zn2+Ion Transportation Across an Interface Using Ion-Chelating Substituted Photochromic 3,3′-Indolospirobenzopyrans: Steric and Electronic Controlling Effects

Modular Counter-Fischer-Indole Synthesis through Radical-Enolate Coupling

A single-electron transfer mediated modular indole formation reaction from a 2-iodoaniline derivative and a ketone has been developed. This transition-metal-free reaction shows a broad substrate scope and unconventional regioselectivity trends. Moreover, important functional groups for further transformation are tolerated under the reaction conditions. Density functional theory studies reveal that the reaction proceeds by metal coordination, which converts a disfavored 5-endo-trig cyclization to an accessible 7-endo-trig process.

A coloring tool for spiropyrans: solid state metal–organic complexation versus salification

Controlling the type of merocyanine metal interaction for broad solid-state coloration.

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

Spiropyrans bearing an N-alkylcarboxylate tether are a common structure in dynamic, photoactive materials and serve as colourimetric/fluorimetric cation receptors. In this study, we describe an efficient synthesis of spiropyrans with 2-12 carbon atom alkylcarboxylate substituents, and a systematic analysis of their interactions with metal cations using 1H NMR and UV-visible spectroscopy. All N-alkylcarboxyspiropyrans in this study displayed a strong preference for binding divalent metal cations and a modest increase in M2+ binding affinity correlated with increased alkycarboxylate tether length.

Quantitative investigations of cation complexation of photochromic 8-benzothiazole-substituted benzopyran: towards metal-ion sensors

The photochromic, thermochromic and metallochromic behaviour of a series of three spiro[indoline-8-(benzothiazol-2-yl)-benzopyrans] has been investigated. The thermodynamic and kinetic parameters of their thermal equilibrium between the ring-closed (spiro) and ring-opened (merocyanine) isomeric forms have been determined using UV-Vis absorption and (1)H NMR spectroscopies. By adding Co(ii) and Ni(ii) ions in acetonitrile solution, 1 : 1 and 1 : 2 metal : merocyanine complexes are formed simultaneously. Using appropriate numerical methods, the kinetic analysis of the complexation allowed us to determine accurately key thermodynamic and spectroscopic parameters of the metal complexes. Results showed that the complexation strength is very sensitive to the size of the indoline nitrogen substituent. Complexation can be reversed by shining white light on the coloured complexes which regenerates the inactive spiropyran form, and releases the metallic ion; hence, these systems display fully reversible negative photochromism. The Zn(ii) complexes exhibit intense fluorescence in the 600-800 nm wavelength range. All these behaviours make these spiropyrans bearing benzothiazole heterocycles promising building blocks for the future construction of photodynamic chemosensors for transition metal ions.