Styryl dyes have been among the most widely used probes for mapping membrane potential changes in excitable cells. However, their utility has been somewhat limited because their excitation wavelengths have been restricted to the 450–550 nm range. Longer wavelength probes can minimize interference from endogenous chromophores and, because of decreased light scattering, improve recording from deep within tissue. In this paper we report on our efforts to develop new potentiometric styryl dyes that have excitation wavelengths ranging above 700 nm and emission spectra out to 900 nm. We have prepared and characterized dyes based on 47 variants of the styryl chromophores. Voltage-dependent spectral changes have been recorded for these dyes in a model lipid bilayer and from lobster nerves. The voltage sensitivities of the fluorescence of many of these new potentiometric indicators are as good as those of the widely used ANEP series of probes. In addition, because some of the dyes are often poorly water soluble, we have developed cyclodextrin complexes of the dyes to serve as efficient delivery vehicles. These dyes promise to enable new experimental paradigms for in vivo imaging of membrane potential.

Cu(I)-catalyzed intramolecular photocycloadditions of diesters made of endo-dicyclopentadiene derivatives linked by the ester bonds with tethers are highly regio- and stereoselective and complete within hours, and the tethers can be easily cleaved afterward upon reduction with LiAlH4-Irradiation of the diesters afforded a 1:1 mixture of the heretofore unknown exo-cis-exo dimer, originating from the (R,S/S,R) diastereomer of the diester and the exo-trans-exo, deriving from the (R,R/S,S) diastereomer. The intermolecular photodimerization yielded, instead, only exo-trans-exo isomers and side products after irradiation for several days. The role of the tether's length and structure on the course of the photocycloadditions was investigated, and it was observed that short tethers introduce considerable strain in the products' framework. Adamantyl-containing tethers provided the shortest reaction times and highest yields. X-ray diffraction analysis of an exo-cis-exo stereoisomer containing adamantane in the tether exhibited an unusually close approach between H atoms on the methylene bridges and a long C-C distance in the cyclobutane ring. A rearrangement induced by X-ray irradiation was observed in this molecule.

Cu(I)-catalyzed intramolecular [2+2] photocycloadditions of two dicyclopentadiene derivatives linked by an alkyl chain have been studied. These reactions are regio- and stereoselective and proceed considerably faster than the corresponding intermolecular reactions. (C) 2000 Elsevier Science Ltd. All rights reserved.