Fluorescent phenanthroimidazoles functionalized with heterocyclic spacers: synthesis, optical chemosensory ability and two-photon absorption (TPA) properties

Abstract

Three series of fluorescent phenanthroimidazoles bearing heterocyclic spacers were synthesized in moderate to excellent yields and evaluated as optical chemosensors for ions as well as two-photon absorbing chromophores. Interaction of compounds 5-7 with anions and cations in acetonitrile and acetonitrile/H2O (95 : 5) showed them to be selective receptors for several anions (AcO-, CN- and F-) and cations (Fe3+, Cu2+ and Pd2+), with compound 7a being the most sensitive receptor for Fe3+ and Cu2+. On the other hand, compounds 5a, 7b and 7c were the most sensitive receptors for AcO-, CN- and F-. The binding stoichiometry between the receptors and the anions and cations was found to be 1 : 2 (ligand to anion/metal cation). The binding process was also followed by H-1 NMR titrations. The evaluation of the TPA properties of chosen phenanthroimidazoles 7a-c by the two-photon induced fluorescence method revealed that compound 7c, which contains a bithienyl spacer, exhibited the highest TPA cross-section (sigma(2)) value.Thanks are due to Fundação para a Ciência e Tecnologia (FCT) for a PhD grant to R. C. M. Ferreira (SFRH/BD/86408/2012), and FEDER (European Fund for Regional Development)-COMPETE-QREN-EU for financial support through the Chemistry Research Centre of the University of Minho (Ref. UID/QUI/00686/2013 and UID/QUI/0686/2016). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. The femto-second laser system was acquired within the framework of the grant REEQ/25/FIS/2005 from the Portuguese Foundation for Science and Technology (FCT).info:eu-repo/semantics/publishedVersio