Boron Dipyrromethene Dyes Bearing Ancillary 2,2′:6′,2″‐Terpyridine Coordination Sites

Abstract

AbstractTwo new boron‐dipyrromethene dyes have been synthesised and their photophysical properties have been investigated by steady‐state and time‐resolved fluorescence spectroscopy. These dyes are equipped with ancillary 2,2′:6′,2″‐terpyridine (terpy) residues, attached either at the B centre or at the meso position of the organic framework; in this latter case two ethynylated pyrene units are bound to the B atom. Under most experimental conditions, the absorption and emission spectral properties are typical of this class of dye. Complexation of zinc(II) cations to the terpy units attached at the B centre causes complete extinction of the fluorescence due to intramolecular electron transfer from the excited state dye to the resultant zinc(II) bis‐terpy complex. Similar behaviour is noted when the terpy is attached at the meso site, although the rate of electron transfer is slower due to the weaker driving force. A most unusual feature of the pyrene‐substituted dye is its facile self association in acetonitrile solution. This results in the reversible formation of a fluorescent associate, believed to be a symmetric dimer, that absorbs and emits to the red of the monomer. Self association is considered to be driven by a solvophobic effect in which the pyrene units seek to minimize surface contact with the surrounding solvent molecules.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)