dipyrromethene and thiophenol

Discrimination between chemically related benzenethiols and aliphatic thiols represents a big problem. In this paper, a fluorescent probe, Bodipy-1, containing an indole-based Bodipy as a fluorophore and a 2,4-dinitrobenzenesulfonyl group as a recognition unit was constructed to achieve the selectivity between them. The Bodipy group in the prepared probe was selectively released through aromatic nucleophilic substitution by thiolate anions from benzenethiols, resulting in blue-red switching in the emission spectra in buffer solutions; that is, two new peaks of the phenol/phenolate state of Bodipy-2 at 565 and 629 nm appeared in emission spectra. By varying the pH value from 6.6 to 8.8, the intensity ratio of I(565)/I(629) varies from 2.0 to 0.3 after complete conversion to Bodipy-2, a ca. 7-fold emission ratio change. This ratiometric emission property by varying the pH value makes Bodipy-1 a promising probe to discriminate benzenethiols from aliphatic thiols by careful selection of the reaction pH.

Topics: Boron Compounds; Buffers; Fluorescent Dyes; Hydrogen-Ion Concentration; Indoles; Molecular Structure; Phenols; Porphobilinogen; Spectrometry, Fluorescence; Sulfhydryl Compounds

A luminescent molecular switch in which the active thiol/disulfide switching element is attached to a meso-phenyl-substituted boron-dipyrromethene (BDP) chromophore as the signalling unit is presented. The combination of these two functional units offers great versatility for multimodal switching of luminescence: 1) deprotonation/protonation of the thiol/thiolate moiety allows the highly fluorescent meso-p-thiophenol-BDP and its nonfluorescent thiolate analogue to be chemically and reversibly interconverted, 2) electrochemical oxidation of the monomeric dyes yields the fluorescent disulfide-bridged bichromophoric dimer, also in a fully reversible process, and 3) besides conventional photoexcitation, the well separated redox potentials of the BDP also allow the excited BDP state to be generated electrochemically (i.e., processes 1) and 2) can be employed to control both photo- and electrochemiluminescence (ECL) of the BDP). The paper introduces and characterizes the various states of the switch and discusses the underlying mechanisms. Investigation of the ortho analogue of the dimer provided insight into potential chromophore-chromophore interactions in such bichromophoric architectures in both the ground and the excited state. Comparison of the optical and redox properties of the two disulfide dimers further revealed structural requirements both for redox switches and for ECL-active molecular ensembles. By employing thiol/disulfide switching chemistry and BDP luminescence features, it was possible to create a prototype molecular ensemble that shows both fully reversible proton- and redox-gated electrochemiluminescence.

Topics: Boron Compounds; Electrochemistry; Fluorescent Dyes; Heterocyclic Compounds, 2-Ring; Luminescent Measurements; Phenols; Porphobilinogen; Sulfhydryl Compounds