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Luminescent Excited‐State Intramolecular Proton‐Transfer (ESIPT) Dyes Based on 4‐Alkyne‐Functionalized [2,2′‐Bipyridine]‐3,3′‐diol Dyes
Author(s) -
Ulrich Gilles,
Nastasi Francesco,
Retailleau Pascal,
Puntoriero Fausto,
Ziessel Raymond,
Campagna Sebastiano
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701803
Subject(s) - photochemistry , chemistry , intramolecular force , excited state , luminescence , terpyridine , bipyridine , singlet state , crystallography , materials science , stereochemistry , crystal structure , organic chemistry , physics , optoelectronics , nuclear physics , metal
Functionalized 6,6′‐dimethyl‐3,3′‐dihydroxy‐2,2′‐bipyridine dyes (BP(OH) 2 ) exhibit relatively intense fluorescence from the relaxed excited state formed by excited‐state intramolecular proton transfer (ESIPT). Bromo functionalization of (BP(OH) 2 ) species followed by palladium(0)‐catalyzed reactions allows the connection (via alkyne tethers) of functional groups, such as the singlet‐emitter diazaboraindacene (bodipy) group or a chelating module (terpyridine; terpy). The X‐ray structure of the terpy‐based compound confirms the planarity of the 3,3′‐dihydroxy‐bipyridine unit. The new dyes exhibit relatively intense emission on the nanosecond timescale when in fluid solution, in the solid state at 298 K, and in rigid glasses at 77 K. In some cases, the excitation wavelength luminescence was observed and attributed to 1) inefficiency of the ESIPT process in particular compounds when not enough vibrational energy is introduced in the Franck–Condon state, which is populated by direct light excitation or 2) the presence of an additional excited state that deactivates to the ground state without undergoing the ESIPT process. For some selected species, the effect of the addition of zinc salts on the absorption and luminescence spectra was investigated. In particular, significant fluorescence changes were observed as a consequence of probable consecutive formation of a 1:1 and 1:2 molecular ratio of ligand/zinc adducts owing to coordination of Zn II ions by the bipyridyldiol moieties, except when an additional terpyridine subunit is present. In fact, this latter species preferentially coordinates to the Zn II ion in a 1:1 molecular ratio and further inhibits Zn II interaction. In the hybrid Bodipy/BP(OH) 2 species, complete energy transfer from the BP(OH) 2 to the bodipy fluorophore occurs, leading to exclusive emission from the lowest‐lying bodipy subunit.