Julia L. Bricks

Syntheses and photophysical properties of a series of cation-sensitive polymethine and styryl dyes

The syntheses and photophysical properties of 20 cation-sensitive fluoroionophores carrying the tetraoxa monoaza 15-crown-5 receptor are described and discussed. Whereas complexation induces only weak effects for the positively charged hemicyanine probes, the closely related styryl dyes show stronger changes in their photophysical properties upon cation binding in the analytically advantageous near-infrared (NIR) region. The strongest effects in both cation-induced spectral effects and complex stability constants are observed for the uncharged probes of styryl base-type, but these probes usually absorb and emit at shorter wavelengths in the UV/VIS region. For both styryl dyes and styryl bases, in some cases cation-induced fluorescence enhancement or quenching is found.

Cation-triggered ‘switching on’ of the red/near infra-red (NIR) fluorescence of rigid fluorophore–spacer–receptor ionophores

Fluorophore–spacer–receptor ionophores 1 and 2 show a strong cation-induced enhancement of the fluorescence at λ > 650 nm in the presence of HgII and AgI (1) or PbII, alkaline-earth and alkali metal ions (2).

A charge transfer-type fluorescent molecular sensor that ?lights up? in the visible upon hydrogen bond-assisted complexation of anionsElectronic Supplementary Information (ESI) available: details on synthesis, X-ray structure analysis, NMR and competition studies. See http://www.rsc.org/suppdata/cc/b4/b405207b/

A charge transfer-type fluorescent molecular sensor consisting of a bisamidopyridine receptor and two styryl base chromophores shows H(2)PO(4)(-) and acetate-enhanced fluorescence due to the conversion of weak intramolecular hydrogen bonds into strong ones in the host-guest ensemble.

Cation Coordination of Bisamidopyridine-derived Receptors as Investigated in the Solid-state and in Solution

A bisamidopyridine-type receptor, N,N′-bis(6-methyl-2-pyridyl)pyridine-2,6-dicarboxamide (1), and its CoIII complex were prepared and their X-ray structures were compared to those of N,N′-diphenylpyridine-2,6-dicarboxamide (2) and CoIII(2)2. Introduction of the two additional coordinative groups resulted in second-order interactions between the central ion and the nitrogen atoms of the terminal pyridine moieties in the crystalline state. Solution studies in acetonitrile revealed the importance of these interactions for the ligands metal ion recognition ability. Whereas 2 only binds to PbII and CuII, 1 yields complexes with a majority of the heavy and transition metal ions studied, CoII, NiII, CuII, ZnII, FeIII, FeII, HgII, and PbII, respectively. The cation binding properties in solution were investigated by absorption spectroscopy and in the case of 1–MII/III, the formation of two spectroscopically distinguishable types of complexes was found. Protonation experiments and theoretical considerations helped to gain further insight into possible modes of coordination in solution.

CT-Operated Bifunctional Fluorescent Probe Based on a Pretwisted Donor–Donor–Biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)–donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D–D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)–acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D – A biphenyls.

Model Systems for the Investigation of the Opsin Shift in Bacteriorhodopsin

Donor-acceptor substituted styrenes and phenylbutadienes with substituents varying in donor and acceptor strength and as reconstituted chromophore-protein complexes were investigated as model compounds for the protonated Schiff base chromophore in bacteriorhodopsin (bR) both experimentally and theoretically. Charge distribution, donor-acceptor strength, and the shift of the absorption energy are correlated. The effect of the external electrostatic field was tested with a compound carrying an additional nonconjugated charge. The concept of overpolarization by the external charge, that is, the reversal of the relative importance of the two main resonance structures in S(0) and S(1), has been emphasized and related to a simple qualitative 2 x 2 interaction model. The variable donor approach is a new way for a better understanding of the Opsin shift in Bacteriorhodopsin.

Long Wavelength Emitting Fluorescence Probes for Metal Ions

Here, three different fluorescence probes for the fluorometric determination of metal ions are presented which emit in the long wavelength spectral region. The spectroscopic behavior of the uncomplexed molecules and their complexes with various metal ions is studied in acetonitrile and compared. The influence of the receptor on both the optical as well as the complexation properties of these modular systems is discussed with respect to the development of design principles for fluorescence probes for heavy and transition metal ions.

Reaction of a N-anthrylcarbonylthiourea derivative with Cu2+ or H+: unusual rearrangement to a highly fluorescent S-(9-anthryl)isothiouronium salt

For the fluorescent ligand 1-(9-anthrylcarbonyl)-3,3-tetramethylenethiourea with Cu(ClO4)2 or strong acids an unusual rearrangement reaction occurred yielding a highly emissive S-(9-anthryl)isothiouronium salt. This rearrangement product was characterised by NMR spectroscopy and X-ray analysis as well as absorption and fluorescence spectroscopy. Additionally, the chemical and complexation behaviour of the N-anthrylcarbonylthiourea derivative is compared to that of its naphthyl and phenyl analogues.