No abstract

New tetrazines substituted by heteroatoms have been synthesized and their electrochemical and photochemical properties investigated. All compounds are reversibly electroactive with standard potentials shifting cathodically according to the donor character of the substituent. The tetrazine derivatives are also fluorescent with maximum emission wavelengths in the range 550-575 nm. Some of them show very long fluorescence lifetimes (several tens of ns) and remain fluorescent in the solid state without major changes in the spectral features. The fluorescence of one of the derivatives can be efficiently quenched by the presence of electron-rich compounds such as triphenylamines, phenol or anisole, which make them very promising compounds for sensor applications.

New fluorescent tetrazines have been prepared and their electrochemistry and fluorescence efficiency evaluated. The occurrence of fluorescence as well as the wavelength were found to be strongly dependent on the substituents, which have to be electronegative heteroatoms. This has been rationalized through a computational study that showed that the crucial factor is the nature of the HOMO, which determines the existence or not of fluorescence. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Several new supramolecular s-tetrazines have been prepared and studied. Their electrochemical and spectroscopic properties have been investigated, especially in the presence of quenchers. Fluorescence quenching has been shown to occur as expected through a charge transfer mechanism and the cyclophane structure has been shown to lead to an acceleration of the quenching process.Scheme 1 Formula of the s-tetrazines.

Synthesis general. Solvents were obtained from SDS and are synthetic grade. Reagents were bought form Aldrich Chemical Co. or AlfaAesar Chemical Co. NMR spectra were measured from CDCl 3 solutions of the samples using a Bruker DPX 400 spectrometer or a JEOL ECS400 spectrometer, with TMS as an internal standard. Syntheses of compounds 5 24b , 6, 10 and 14 31 have been published elsewhere. Scheme S1. Synthesis of ketoximes 10-13 from [2.2]paracyclophane. General procedure for the synthesis of ketones 7-9 [2.2]Paracyclophane (1 eq.) is dissolved in dichloromethane (c=0.1 mol.L-1), stirred and cooled at 0° in an salt-ice bath. The acid chloride (2.1 eq.) and aluminum chloride (1.75 eq.) are suspended in dichloromethane (c=1 mol.L-1), cooled at 0°C and added quickly to the [2.2]paracyclophane solution under rapid stirring. Reaction mixture is maintained at 0°C for 15 min, pored onto ice and vigorously stirred until the organic layer becomes colorless. Diethyl ether is added until the organic layer becomes less dense than water. The organic layer is separated, washed twice with a saturated NaHCO 3 aqueous solution and finally with a a saturated NaCl aqueous solution. The organic layer is dried on MgSO 4 and the solvents are removed under reduced pressure. The crude product is purified by column chromatography on SiO 2. Elution petroleum ether/dichloromethane 3:2 v/v to remove the unreacted

No abstract

The fluorescence photoswitching of photochrome-fluorophore (PF) mixtures based on 1,2-bis(5′-ethoxy-2′-(2”-pyridyl) thiazolyl) perfluorocyclopentene (P) and pyrromethene 597 (F) were studied. Polymethylmethracrylate (PMMA) films were fabricated with respective concentrations of 1.0 × 10−2 mol L−1 for P, and 9.2 × 10−4 and 9.2 × 10−3 mol L−1 for F. By alternate UV (λOF = 334 nm) and visible (λCF = 547 nm) irradiations, inducing the reaction between the opened (P-OF) and closed (P-CF) forms of P, both fluorescence intensity and lifetime can be reversibly modified and visualized in the micrometer scale by fluorescence imaging. Switching (writing/erasing) and reading functions are respectively borne by P and F. The interaction between the two units owes to an energy transfer based quenching of fluorescence, which operates in the P-CF state but not P-OF. The reading process alters only very weakly the state of P. During the writing process, the presence of F accelerates the P-CF to P-OF reaction, as evidenced by following the absorption spectrum change. The efficiency of the energy transfer was determined by Gösele’s model for the two concentrations of F and for concentrations of P-CF from 0 to 1.0 × 10−2 mol L−1. This model fits well with the experimental fluorescence intensity change during the photoreaction and can account for the origin of the above-mentioned acceleration. In addition, we demonstrated that switching one molecule of P-OF to P-CF could quench up to eight molecules of F. This “amplification” of the fluorescence signal was modeled as a function of the concentrations of both species, providing a tool to optimize the PF system composition.

No abstract