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1.
J Org Chem ; 76(12): 4859-73, 2011 Jun 17.
Article in English | MEDLINE | ID: mdl-21506604

ABSTRACT

Four azulene dyads have been synthesized and studied by spectroscopic and electrochemical methods. A triarylamine, a boron-dipyrromethene (BDP or BODIPY), a porphyrin, and an isoalloxazine moiety have been linked to an extended π electron system at the 2-position of azulene, leading to the dyads 1-4, respectively. For the synthesis of 1-4, first 2-(4-ethynyl-phenyl)azulene (EPA) was prepared, which was further reacted with the halogenated chromophores by Pd-catalyzed cross-coupling reactions. The dyads 1-4 exhibit strong absorption bands in the visible range, which are dominated by the absorption spectra of the individual subchromophores. Fluorometric studies of 2-4 revealed that after excitation of the subchromophoric unit attached to the parent azulene moiety, quenching mainly through energy transfer to azulene is effective, whereas possible charge-transfer interactions play only a minor role. Potentiodynamic oxidation of the dyads 1-4 leads to the formation of polymer films, which are deposited at the electrode. The polymer film derived from 1 was further characterized by spectroelectrochemistry. During positive doping of poly-1, a strong absorption band appears at 13,200 cm(-1), which is typical for triarylamine radical cations. This band is overlapping with a broad absorption band in the low-energy region that might be caused by charge-transfer interactions within the polymer.

2.
Chemistry ; 13(32): 8998-9003, 2007.
Article in English | MEDLINE | ID: mdl-17705328

ABSTRACT

An asymmetrically core-extended boron-dipyrromethene (BDP) dye was equipped with two electron-donating macrocyclic binding units with different metal ion preferences to operate as an ionically driven molecular IMPLICATION gate. A Na(+)-responsive tetraoxa-aza crown ether (R(2)) was integrated into the extended pi system of the BDP chromophore to trigger strong intramolecular charge transfer (ICT(2)) fluorescence and guarantee cation-induced spectral shifts in absorption. A dithia-oxa-aza crown (R(1)) that responds to Ag(+) was attached to the meso position of BDP in an electronically decoupled fashion to independently control a second ICT(1) process of a quenching nature. The bifunctional molecule is designed in such a way that in the absence of both inputs, ICT(1) does not compete with ICT(2) and a high fluorescence output is obtained (In(A)=In(B)=0-->Out=1). Accordingly, binding of only Ag(+) at R(1) (In(A)=1, In(B)=0) as well as complexation of both receptors (In(A)=In(B)=1) also yields Out=1. Only for the case in which Na(+) is bound at R(2) and R(1) is in its free state does quenching occur, which is the distinguishing characteristic for the In(A)=0 and In(B)=1-->Out=0 state that is required for a logic IMPLICATION gate and Boolean operations such as IF-THEN or NOT.


Subject(s)
Boron Compounds/chemistry , Fluorescent Dyes/chemistry , Porphobilinogen/analogs & derivatives , Boron Compounds/chemical synthesis , Fluorescence , Ions/chemistry , Molecular Structure , Porphobilinogen/chemistry , Quantum Theory
3.
Langmuir ; 22(5): 2378-83, 2006 Feb 28.
Article in English | MEDLINE | ID: mdl-16489832

ABSTRACT

A flavin-modified gold electrode was developed in order to catalyze the electrochemical oxidoreduction of flavoproteins. Surface modification was carried out by a two-step procedure. In the first step a mixed self-assembled monolayer obtained by adsorption of activated and nonactivated 3,3'-dithiopropionic acid (free acid and N-succinimidyl ester) was formed, followed by the covalent attachment of a N(10)-hexylamino-alkylated flavin derivative via an amide bond in the second step. The electrochemical properties of the flavin-modified electrode are presented and discussed. The redox potential of the attached flavin was measured at various pH values and the electron-transfer rate constant between electrode and flavin was determined as k0 = 5 s(-1) independent of pH. The flavin-modified electrode was successfully applied to the electrochemical and spectroelectrochemical investigation of the flavoprotein WrbA from Escherichia coli that shows some structural similarities to flavodoxins. It is concluded that the electron transfer "electrode --> flavin --> flavoprotein" occurs by a two-step hopping mechanism where the first step is rate determining. Kinetic details are discussed. Furthermore, it turned out that, in contrast to flavodoxins, where the semiquinone state is stabilized, WrbA rapidly takes up two electrons, directly leading to the fully reduced form. The presented electrode surface modification may generally lend itself for spectroelectrochemical investigations of flavoproteins.


Subject(s)
Flavoproteins/chemistry , Adsorption , Coated Materials, Biocompatible , DNA-Binding Proteins/chemistry , Electrochemistry , Electrodes , Escherichia coli Proteins/chemistry , Flavins/chemistry , Gold , Hydrogen-Ion Concentration , Repressor Proteins/chemistry , Surface Properties
4.
Chemistry ; 12(3): 689-700, 2006 Jan 11.
Article in English | MEDLINE | ID: mdl-16231292

ABSTRACT

A luminescent molecular switch in which the active thiol/disulfide switching element is attached to a meso-phenyl-substituted boron-dipyrromethene (BDP) chromophore as the signalling unit is presented. The combination of these two functional units offers great versatility for multimodal switching of luminescence: 1) deprotonation/protonation of the thiol/thiolate moiety allows the highly fluorescent meso-p-thiophenol-BDP and its nonfluorescent thiolate analogue to be chemically and reversibly interconverted, 2) electrochemical oxidation of the monomeric dyes yields the fluorescent disulfide-bridged bichromophoric dimer, also in a fully reversible process, and 3) besides conventional photoexcitation, the well separated redox potentials of the BDP also allow the excited BDP state to be generated electrochemically (i.e., processes 1) and 2) can be employed to control both photo- and electrochemiluminescence (ECL) of the BDP). The paper introduces and characterizes the various states of the switch and discusses the underlying mechanisms. Investigation of the ortho analogue of the dimer provided insight into potential chromophore-chromophore interactions in such bichromophoric architectures in both the ground and the excited state. Comparison of the optical and redox properties of the two disulfide dimers further revealed structural requirements both for redox switches and for ECL-active molecular ensembles. By employing thiol/disulfide switching chemistry and BDP luminescence features, it was possible to create a prototype molecular ensemble that shows both fully reversible proton- and redox-gated electrochemiluminescence.


Subject(s)
Boron Compounds/chemistry , Fluorescent Dyes/chemistry , Heterocyclic Compounds, 2-Ring/chemistry , Phenols/chemistry , Porphobilinogen/analogs & derivatives , Sulfhydryl Compounds/chemistry , Electrochemistry , Luminescent Measurements , Porphobilinogen/chemistry
6.
J Am Chem Soc ; 127(39): 13522-9, 2005 Oct 05.
Article in English | MEDLINE | ID: mdl-16190715

ABSTRACT

Incorporation of a tailor-made size-restricted dithia-aza-oxa macrocycle, 1-oxa-4,10-dithia-7-aza-cyclododecane, via a phenyl linker into two fluorescent sensor molecules with electronically decoupled, rigidly fixed, and sterically preoriented architectures, a 1,3,5-triaryl-Delta2-pyrazoline and a meso-substituted boron-dipyrromethene (BDP), yields amplified fluorescence in the red-visible spectral range upon binding of Fe(III) ions. The response to Fe(III) and potentially interfering metal ions is studied in highly polar aprotic and protic solvents for both probes as well as in neat and buffered aqueous solution for one of the sensor molecules, the BDP derivative. In organic solvents, the fluorescence of both indicators is quenched by an intramolecular charge or electron transfer in the excited state and coordination of Fe(III) leads to a revival of their fluorescence without pronounced spectral shifts. Most remarkably, the unbound BDP derivative shows dual emission in water and can be employed for the selective ratiometric signaling of Fe(III) in buffered aqueous solutions.

7.
Chemistry ; 11(20): 5843-8, 2005 Oct 07.
Article in English | MEDLINE | ID: mdl-16041808

ABSTRACT

In a one-pot reaction of N-(5-methylthiazole-2-yl)-thiazole-2-carboxamide HL2 (3) with iron(II) acetate in air, the homotrinuclear heteroleptic mixed-valent oxo-centered iron cluster [Fe(II)Fe(III)O(L2)3(OAc)3] (4) was formed. Exchange of iron(II) in 4 by nickel(II) afforded the heteronuclear cluster [Ni(II)Fe(III)O(L2)3(OAc)3] (6). To obtain crystals suitable for X-ray structure analyses, in 4 and 6, the OAc- co-ligands were exchanged by OBz- ligands to give [Fe(II)Fe2(III)O(L2)3(OBz)3] (5) and [Ni(II)Fe(III)O(L2)3(OBz)3] (7). The complexes 5 and 7 are isostructural and made up of three ditopic, tridentate ligands (L2)- and three bridging benzoate co-ligands, which fix the three metal ions in the corners of a triangle with an mu3-O2- ion in the center. The mixed-valent character of 4-7, their intramolecular electron-exchange processes, and their redox properties were studied by variable-temperature Mössbauer spectroscopy and cyclic voltammetry.

8.
J Am Chem Soc ; 127(9): 3156-64, 2005 Mar 09.
Article in English | MEDLINE | ID: mdl-15740155

ABSTRACT

Several squaraine tethered bichromophoric podand systems 1a-d and a monochromophoric analogue 2 were prepared and characterized. Among these, the bichromophore, 1b, containing five oxygen atoms in the flexible podand moiety was found to specifically bind Ca(2+) in the presence of other metal ions such as K(+), Na(+), and Mg(2+). The selective binding of Ca(2+) is clear from the absorption and emission spectral changes as well as by the visual color change of 1b from light-blue to an intense purple-blue. Benesi-Hildebrand and Job plots confirmed a 1:1 binding between 1b and Ca(2+). Signaling of the binding event is achieved by the cation-induced folding of the bichromophore and the resultant exciton coupling between the squaraine chromophores. The monochromophoric squaraine dye 2 failed to give optical signals upon Ca(2+) binding, due to the absence of exciton interaction in the bound complex. Titration of the folded complex 9 with EDTA released the metal ion from the complex, thereby regaining the original absorption and emission properties of the bichromophore. The squaraine foldamer 1b reported here is the first example of a selective chromogenic Ca(2+) sensor, which works on the principle of exciton interaction in the folded Ca(2+) complex of a bichromophore, the optical properties of which are similar to those of the "H"-type aggregates of analogous squaraine dyes.


Subject(s)
Biosensing Techniques/methods , Calcium/analysis , Cyclobutanes/chemistry , Phenols/chemistry , Calcium/chemistry , Cations, Monovalent , Edetic Acid/chemistry , Electrochemistry , Magnetic Resonance Spectroscopy , Metals/chemistry , Spectrophotometry , Substrate Specificity
10.
Org Lett ; 5(17): 2975-8, 2003 Aug 21.
Article in English | MEDLINE | ID: mdl-12916959

ABSTRACT

[reaction: see text] The redox chemistry of pi-extended squaraines is investigated using cyclic voltammetry, in-situ spectroelectrochemistry and quantum chemical calculations. Squaraine 1 is reversibly oxidized to the radical cation and dication whereas reduction shows limited electrochemical but fully chemical reversibility. The radical cation of 1 reveals absorption bands at 1000 nm and a "two-band feature" at 1600 nm. Their implications on the intramolecular electron transfer are discussed.

11.
Chemistry ; 8(17): 4008-16, 2002 Sep 02.
Article in English | MEDLINE | ID: mdl-12360942

ABSTRACT

The photoreactions of the 1,1-dicyano-2,2-diphenyl-1,2-dihydronaphthalene (DHN-1) have been studied by photochemical techniques under various conditions at room temperature. A transient species, T(C), with a major maximum at 545 nm in the UV-visible spectrum, detected in small yield in polar aprotic solvents and in large yield in trifluoroethanol (TFE) and hexafluoropropan-2-ol (HFP), is assigned as a carbocation (1-cyano-2,2-diphenylnaphthalenium), which is generated photochemically by elimination of CN(-). The decay of T(C) was found to be a first-order process in HFP, in which the longest lifetime of 0.4 s was observed; in TFE, the carbocation decays on the ms timescale, while the shortest lifetime of 1 micros was found in ethanol. The yield of T(C) increases strongly upon addition of water to alcohols or acetonitrile, and remains substantial in the presence of large amounts of water (1-20 M). On addition of water to TFE or HFP, the lifetime of the carbocation becomes much shorter. This is supported by pulse-induced charge formation due to the carbocation and release of CN(-); the conductivity decay is related to the lifetime of the carbocation under selected conditions. In addition, a major irreversible and a minor thermally reversible photoprocess were spectroscopically observed in solvents of low as well as high polarity. The former photoproduct, absorbing below 300 nm, is tentatively ascribed to benzobicyclohexenes A produced by phenyl-vinylmethane rearrangement. In the latter process, a longer-lived benzoquinodimethane derivative B, having a maximum at 400-430 nm, is formed; this is related to ring opening and closure and represents a new example of photochromic ten-electron electrocyclisation. The distinct differences between the photochromism of DHN and that of dihydroazulene (DHA) stem mainly from stereoelectronic effects. This study, however, has also revealed that photochemically induced bond heterolysis and photochemical/thermal electrocyclisation, representing two basic processes of photochromism, may occur in one molecular unit.

12.
Chemistry ; 8(16): 3614-9, 2002 Aug 16.
Article in English | MEDLINE | ID: mdl-12203287

ABSTRACT

Starting from closely related metal-ligand combinations, completely different oligomeric metal clusters are synthesized. Whereas, picoline-tetrazolylamide HL(1) (1) and zinc or nickel acetate afforded [2x2] grids [M(4)(L(1))(8)] (2), slightly different N-(2-methylthiazole-5-yl)-thiazole-2-carboxamide HL(2) (5 a) and nickel acetate yielded the monometallic complex [Ni(L(2))(2)(OH(2))(2)] (6). In contrast, reaction of 5 a with zinc acetate produced the tetrametallic zinc cluster [Zn(4)O(L(2))(4)(OAc)(2)] (7). Even more surprising, when 3-methyl-substituted HL(3) (5 b) instead of 2-methyl-substituted HL(2) (5 a) was allowed to react under identical conditions with zinc acetate, the cluster [Zn(4)O(L(3))(4)Cl(2)] (8) crystallized from dichloromethane. Clusters 7 and 8 are isostructural. As for 7, in 8 two of the edges of the tetrahedron of zinc ions are doubly bridged, two are singly bridged, and the other two are nonbridged. On the other hand, when iron(II) acetate under aerobic conditions was allowed to react with 5 a, the unprecedented complex [[Fe(3)O(L(2))(2)(OAc)(4)](2)O] (9) was isolated. Cluster 9 is composed of two trimetallic, triangular mu(3)-O(2-)-centered [Fe(3)O(L(2))(2)(OAc)(4)](+) modules, linked by an almost linear mu(2)-O(2-) bridge. The Mössbauer spectrum together with cyclic voltammetric and square-wave voltammetric measurements of 9 are reported, and 6-9 were characterized unequivocally by single-crystal X-ray structure analyses.

13.
J Am Chem Soc ; 124(11): 2438-9, 2002 Mar 20.
Article in English | MEDLINE | ID: mdl-11890783

ABSTRACT

The photochromic couple dihydroazulene/vinylheptafulvene (DHA/VHF) is an established system for molecular switching. The photoinduced ring opening of the thermally stable dihydroazulene proceeds in the picosecond time regime with subsequent rapid relaxation to the electronic ground state. So far it was not possible to reverse the reaction photochemically. It was always found that the back reaction proceeds thermally on a longer time scale. In the case of the cyanophenyl-DHA derivative utilized in the present study, this is accounted to s-cis/s-trans isomerization of the primarily formed s-cis VHF. Since this particular isomerization takes much longer than nanoseconds, we now successfully applied a second visible femtosecond pulse subsequent to the initial UV pulse (25 ps delay) achieving ring closure of the primarily formed s-cis VHF. The now bidirectional photoswitching was monitored by the changes in the cw spectrum. As a result, the DHA/VHF system is found to be a multifold switchable system by itself: it is both a very fast photoreversible switch and a photochemical/thermal switch with a thermal lock mode.


Subject(s)
Cycloheptanes/chemistry , Cyclopentanes/chemistry , Vinyl Compounds/chemistry , Azulenes , Photochemistry , Spectrophotometry, Ultraviolet
14.
Org Lett ; 4(5): 683-6, 2002 Mar 07.
Article in English | MEDLINE | ID: mdl-11869101

ABSTRACT

[structure: see text] The synthesis of two optically active pyrene-modified cyclic hexapetides and their selectivity toward the complexation of alkaline earth metal ions are reported. Complexation was studied by optical and chiroptical methods. The cyclic peptides are forming 2:1 sandwich complexes with the metal ions.


Subject(s)
Peptides, Cyclic/chemistry , Pyrenes/chemistry , Calcium/analysis , Calcium/chemistry , Calcium/metabolism , Fluorescent Dyes/chemistry , Metals, Alkaline Earth/analysis , Metals, Alkaline Earth/chemistry , Metals, Alkaline Earth/metabolism , Models, Molecular , Molecular Probes/chemistry , Oligopeptides/chemistry , Oligopeptides/metabolism , Optical Rotation , Peptides, Cyclic/metabolism , Spectrometry, Fluorescence , Titrimetry
17.
Angew Chem Int Ed Engl ; 40(2): 385-387, 2001 Jan 19.
Article in English | MEDLINE | ID: mdl-29712397

ABSTRACT

The highly fluorescent, unsymmetrically substituted boron-dipyrromethene dye 1 shows emission features that are strongly dependent on the solvent polarity. Thus, 1 can be used for highly sensitive fluorometric probing of solvent polarity and acidity and furthermore can be switched chemically or electrochemically in the near infrared.

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