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The non-fluorescent 9-nitrobenzo[b]quinolizinium is readily reduced by nitroreductase to a fluorescent reaction product. The resulting light-up effect enables the selective detection of nitro-reductase activity in vitro and in Escherichia coli bacterial cultures.

The 9‐ and 12‐dimethylaminophenyl‐substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki‐Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4‐DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA‐melting analysis. Both ligands bind to duplex DNA by intercalation and to G4‐DNA by terminal π stacking. At neutral conditions, they bind with higher affinity (K b=105−106 M−1) to representative quadruplex forming oligonucleotides 22AG, c‐myc, c‐kit, and a2, than to duplex calf thymus (ct) DNA (K b=5‐7×104 M−1). At pH 5, however, the affinity of 3 a towards G4‐DNA 22AG is higher (K b=1.2×106 M−1), whereas the binding constant towards ct DNA is lower (K b=3.9×103 M−1) than under neutral conditions. Notably, the association of the ligand with DNA results in characteristic changes of the absorption and emission properties under specific conditions, which may be used for optical DNA detection. Other than the parent berberine, the ligands do not show a noticeable increase of their very low intrinsic emission intensity upon association with DNA at neutral conditions. In contrast, a fluorescence light‐up effect was observed upon association to duplex (Φ fl=0.01) and quadruplex DNA (Φ fl=0.04) at pH 5. This fluorimetric response to G4‐DNA association in combination with the distinct, red‐shifted absorption under these conditions provides a simple and conclusive optical detection of G4‐DNA at lower pH., The very weak fluorescence of 4‐dimethylaminophenyl‐substituted berberines only increases significantly if both their conformational flexibility is strongly restricted, i. e. in viscous medium or when bound to quadruplex DNA, and the amino group is protonated at low pH. This requirement of a dual stimulation to cause a light‐up effect enables the spectrometric detection of quadruplex DNA at pH 5.

The suitability of 3-hydroxy-4-pyridylisoquinoline to operate as fluorescent chemosensor for the detection of metal ions was investigated. For that purpose, the interactions of the title compound with selected metal ions were investigated by absorption and emission spectroscopy. The complexation of Zn2+, Fe2+, Mg2+ with 1:1 and 2:1 stoichiometry leads to characteristic optical responses that depend significantly on the employed solvents, thus allowing for the fluorimetric identification and detection of particular metal cations in a matrix-based pattern analysis or by fluorimetric titrations. Graphical abstract

A novel type of azoniahetarene, namely, benzo[

The combination of styryl dye properties with the acidity and strong photoacidity of the 2,2′‐[(1′′‐hydroxy‐4′′‐methyl‐(E)‐2′′,6′′‐phenylene)]‐bisquinolizinium enables the detection of DNA by distinct absorption and emission color changes and the fluorimetric detection of DNA in cells with epifluorescence and confocal fluorescence microscopy.

A phosphate-substituted, zwitterionic berberine derivative was synthesized and its binding properties with duplex DNA and G4-DNA were studied using photometric, fluorimetric and polarimetric titrations and thermal DNA denaturation experiments. The ligand binds with high affinity toward both DNA forms (Kb = 2–7 × 105 M−1) and induces a slight stabilization of G4-DNA toward thermally induced unfolding, mostly pronounced for the telomeric quadruplex 22AG. The ligand likely binds by aggregation and intercalation with ct DNA and by terminal stacking with G4-DNA. Thus, this compound represents one of the rare examples of phosphate-substituted DNA binders. In an aqueous solution, the title compound has a very weak fluorescence intensity (Φfl &lt, 0.01) that increases significantly upon binding to G4-DNA (Φfl = 0.01). In contrast, the association with duplex DNA was not accompanied by such a strong fluorescence light-up effect (Φfl &lt, 0.01). These different fluorimetric responses upon binding to particular DNA forms are proposed to be caused by the different binding modes and may be used for the selective fluorimetric detection of G4-DNA.

Quadruplex DNA, which is a relevant target for anticancer therapies, may alter its conformation because of interactions with interfaces. In pursuit of a versatile methodology to probe adsorption-induced conformational changes, the interaction between a fluorescent [2.2.2]heptamethinecyanine dye and quadruplex DNA (G4-DNA) was studied in solution and on surfaces. In solution, the cyanine dye exhibits a strong light-up effect upon the association with G4-DNA without interference from double-stranded DNA. In addition, a terminal π-stacking as a binding mode between the cyanine dye and G4-DNA is concluded using NMR spectroscopy. To unravel the effects of adsorption on the conformation of quadruplex-DNA, G4-DNA, and double-stranded and single-stranded DNA were adsorbed to positively charged poly(allylamine) hydrochloride (PAH) surfaces, both in planar and in constrained 55 nm diameter aluminum oxide nanopore formats. All DNA forms showed a very strong affinity to the PAH surfaces as shown by surface plasmon resonance and reflectometric interference spectroscopy. The significant increase of the fluorescence emission intensity of the cyanine light-up probe observed exclusively for surface immobilized G4-DNA affords evidence for the adsorption of G4-DNA on PAH with retained quadruplex conformation.

9-Arylbenzo[b]quinolizinium derivatives were prepared with base-free Suzuki–Miyaura coupling reactions between benzo[b]quinolizinium-9-trifluoroborate and selected benzenediazonium salts. In addition, the Sonogashira coupling reaction between 9-iodobenzo[b]quinolizinium and the arylalkyne derivatives yielded four novel 9-(arylethynyl)benzo[b]quinolizinium derivatives under relatively mild reaction conditions. The 9-(N,N-dimethylaminophenylethynyl)benzo[b]quinolizinium is only very weakly emitting, but the emission intensity increases by a factor >200 upon protonation, so that this derivative may operate as pH-sensitive light-up probe. Photometric and fluorimetric titrations of duplex and quadruplex DNA to 9-(arylethynyl)benzo[b]quinolizinium derivatives revealed a significant binding affinity of these compounds towards both DNA forms with binding constants of Kb = 0.2–2.2 × 105 M−1.

3-Hydroxynaphtho[1,2-b]quinolizinium was synthesized by cyclodehydration route and its optical properties in different media were investigated. The absorption and emission spectra of this compound depend on the pH of the solution. Thus, at higher pH values the deprotonation yields a merocyanine-type dye that exhibits significantly red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pKa = 7.9), it has a strongly increased acidity in the excited state (pKa* = 0.4). As a result, the blue-shifted fluorescence of the hydroxyquinolizinium becomes dominant only under strongly acidic conditions. In addition, it is shown that 3-hydroxynaphtho[1,2-b]quinolizinium binds to cucurbit[7]uril (CB[7]) with moderate affinity (Kb = 1.8 × 104 M−1, pH 5) and that the pKa and pKa* values of this ligand increase by about two to three orders of magnitude, respectively, when bound to CB[7].

Six new 8-styryl-substituted coralyne derivatives 4a–f were synthesized from coralyne (2) by a base catalysed Knoevenagel type reaction. It was shown by photometric and fluorimetric titrations of double stranded and quadruplex DNA to 4b–d as well as by fluorimetric DNA denaturation experiments that these ligands bind to DNA with different binding modes at varying ligand-DNA ratios (LDR). Specifically, the addition of DNA caused initially a hypochromic effect in absorbance and, at a particular LDR, the development of a new red shifted absorption band with a hyperchromic effect. Furthermore, 4b–d induced a significant and selective stabilization of quadruplex DNA towards unfolding (ΔTm = 31.6–32.9 °C at LDR = 5), which is even more pronounced as compared to the parent compound coralyne (2). Most notably, the addition of DNA to the dimethylamino-substituted derivative 4b leads to a new, strongly red-shifted emission band at 695 nm. Hence, this derivative is a fluorescent probe that changes its fluorescence colour from green to red in the presence of DNA and even allows the fluorimetric analysis of living cells by staining of the nucleoli.

(E)-2-[1′-((Diphenylamino)styryl)quinolizinium (3a) and 2,2′-{(phenylimino)-bis[(E)-1′′,1′′′-styryl]}-bis[quinolizinium] (3b) were synthesized, and their interactions with duplex DNA and quadruplex DNA were investigated with a particular focus on their ability to operate as DNA-sensitive fluorescent probes. Due to the significantly different size and steric demand of these quinolizinium derivatives they exhibit different binding modes. Thus, 3a intercalates into duplex DNA and binds through π stacking to quadruplex DNA, whereas 3b favours groove binding to both DNA forms. The emission intensity of these compounds is very low in aqueous solution, but it increases drastically upon association with duplex DNA by a factor of 11 (3a) and >100 (3b) and with quadruplex DNA by a factor of >100 (3a) and 10 (3b), with emission bands between 600 and 750 nm.

It is shown by photometric and fluorimetric analysis, along with supporting theoretical calculations, that hydroxy-substituted benzo[b]quinolizinium derivatives display the characteristic features of organic photoacids. Specifically, the experimental and theoretical results confirm the strong acidity of these compounds in the excited state (pKa* < 0). The combination of the prototropic properties of 8- and 9-hydroxybenzo[b]quinolizinium with the particular solvent–solute interactions of the excited acid and its conjugate base leads to a pronounced fluorosolvatochromism, hence the emission maxima shift from 468 nm (8-hydroxybenzo[b]quinolizinium) or 460 nm (9-hydroxybenzo[b]quinolizinium) in CH3CN to 507 and 553 nm in DMF, respectively. This novel type of photoacid represents several features that may be used for applications as water-soluble fluorescent probes or as a source for the photoinduced supply of acidity.

In this Account our efforts are described to establish the benzo(b)quinolizinium ion, also known as acridizinium or 4a-azoniaanthracene, as a water-soluble surrogate of anthracene for the development of selective fluorescent probes. It is demonstrated with selected examples that especially the 9-aminobenzo(b)quinolizinium is a donor-acceptor dye with favorable absorption and emission properties and may be used as a versatile building block for fluorescent light-up probes and ratiometric probes.

A series of new fluorescent arylstyrylimidazo[1,2-a]pyridines was synthesized and fully characterized. It is observed that the E isomers are stable in the solid state and in solutions. The absorption and emission properties of the compounds changed drastically upon acidification. The compounds showed good thermal stability for practical applications. In addition, antimicrobial, antioxidant, and DNA-cleavage activity of the compounds were examined. The results indicate that the compounds did not show any antimicrobial and antioxidant activity. However, they caused decreased mobility of form I DNA and also showed DNA cleavage activity. (C) 2015 Elsevier B.V. All rights reserved.

A series of novel fluorescent arylstyrylimidazo[1,2-a]pyridines was synthesized and fully characterized. All styryl derivatives have an E-configuration of the vinyl double bond as unequivocally shown by H-1 NMR spectroscopy. It was observed that the E isomers are stable in the solid state; however, the derivatives with strong electron donating dialkylamino substituents underwent partial E-Z isomerization in solution at room temperature. The styryl derivatives absorb in the UV or visible region and emit light with moderate Stokes shifts. These compounds exhibit fluorosolvatochromism, namely the emission band is red shifted with increasing solvent polarity. Moreover, the absorption and emission properties of the styryl derivatives change drastically upon acidification, as the protonation of the nitrogen atoms of the imidazo[1,2-a]pyridine ring increases the donor-acceptor interplay of the pi system. (C) 2014 Elsevier Ltd. All rights reserved.

A series of monomeric and homodimeric 4-alkoxystyryl(pyridinium) dyes was synthesized and their DNA-binding properties were investigated. We found that the length of the alkyl substituent has a crucial influence on the binding mode of the dyes, although the structure of the DNA-binding unit is the same for all compounds. Remarkably, mono- and bis-styryl derivatives comprising an oxodecyl chain represent the rare examples of small molecules that bind to the major groove of DNA. We have also demonstrated that the dyes, except the monostyryl dye with a bromopropyl substituent, form chiral aggregates in the presence of double-stranded DNA.

The solvatochromic 9-hydroxybenzo[b]quinolizinium ion is shown to operate as fluorescent probe for the detection of water in acetonitrile. The dual fluorescence of this photoacid and its dependence on the content of water in the medium enable the ratiometric analysis of the fluorescence data. Graphical Abstract ᅟ.

The visualization of cell components or processes within cells is an essential task in bioanalytical chemistry. Specifically, the fluorimetric detection of biomacromolecules has developed as a key technique in this research area, mainly because emission spectroscopy is a highly sensitive and straightforward method with relatively few demands on the equipment. As a consequence, several fluorescent probes have been established that enable the selective detection of cells or cellular components. For example, DNA–fluorophore conjugates, peptide-based molecular beacons, groove-binding cyanine dyes, and light-cleavable caged dyes were shown to operate as DNA stains in live cells. Similarly, it was demonstrated that appropriately substituted metallointercalators have a high propensity to bind to cellular DNA and thus enable its fluorimetric detection, or, in some cases, the detection of other cell components. 11] The same principle was applied to detect RNA in nucleoli and the cytoplasm with a 2,7-carbazole derivative. Furthermore, exciton-controlled hybridization-sensitive fluorescent oligonucleotide (ECHO) probes allow multicolor RNA imaging in cells. Recently, a chemosensor has been presented that enables the fluorimetric differentiation of quadruplex DNA from other nucleic acids in cells. Moreover, it has been shown that the fluorimetric discrimination of regions with different polarities may be accomplished in cells with quinoxaline derivatives. Along these lines, the use of near-infrared (NIR, 650–900 nm) fluorescent probes is advantageous for biological applications, because NIR fluorophores exhibit low or almost no phototoxicity, relatively deep penetration into tissue, and negligible interference with the autofluorescence of cells. We have shown recently that benzo[b]quinolizinium derivatives may be functionalized such that the fluorescence is quenched by different independent deactivation pathways and that the association with biomacromolecules results in light-up effects and shifts in the emission energy. In some cases, separate deactivation channels enable the indepenACHTUNGTRENNUNGdent or even simultaneous detection of DNA and metal ions with one chemosensor. In this context, we synthesized 9-(4-dimethylamino)benzo[b]quinolizinium (1a), which exhibits a very low emission quantum yield, presumably caused by deactivation of the excited state by torsional relaxation and photoinduced electron transfer (PET) or charge shift (CS). Notably, some structural features of the derivative 1a resemble aminophenylpyridinium derivatives such as 2, which have been used as fluorescent probes in nerve membranes, and Thioflavin T (3), which has been applied for fluorimetric analysis of amyloid fibril formation. Therefore, we proposed that the derivative 1a may represent a complementary fluorimetric tool for the selective analysis of biomacromolecules, especially considering our experience with the benzo[b]quinolizinium ion as a ligand for DNA and proteins. Herein, we demonstrate that different physiologically relevant host systems are stained with the chemosensor 1a, most remarkably with different emission wavelengths and intensities. In addition, we show that, due to these properties, the chemosensor 1a represents one of the rare examples of probes that stain cells with multicolored fluorescence.

Cationic biaryl derivatives were synthesized by Suzuki–Miyaura coupling of 3-bromonaphtho[1,2-b]quinolizinium bromide with arylboronic acids. The resulting cationic biaryl derivatives exhibit pronounced fluorosolvatochromic properties. First photophysical studies in different solvents showed that the emission energy of the biaryl derivatives decreases with increasing solvent polarity. This red-shifted emission in polar solvents is explained by a charge shift (CS) in the excited state and subsequent solvent relaxation. Furthermore, the polarity of protic polar and aprotic polar solvents affects the emission energy to different extent, which indicates a major influence of hydrogen bonding on the stabilization of the ground and excited states.

The blue fluorescence of acridizinium bromide (ADZ+) and the green fluorescence of 9-aminoacridizinium bromide (AADZ+) in aqueous solutions can be almost entirely switched off upon the double inclusion of these guests in the cavity of cucurbit[8]uril (CB[8]) owing to the formation of a nonfluorescent, noncovalent dimer complex, and then fluorescence can be effectively restored by adding cucurbit[7]uril (CB[7]) to the complex because it competitively extracts the fluorophores out of the CB[8] cavity.

The time-resolved emission properties of selected anthracene derivatives, namely anthracene (1a), 2-methylanthracene (1b), 2-chloroanthracene (1c), 2-methoxyanthracene (1d), 2-methoxy-6-methylanthracene (1e), 2-(N,N'-dicyclohexylureidocarbonyl)-6-methoxyanthrace ne (1f), 2-(6-methoxyanthr-2-yl)-4,4-dimethyl-2-oxazoline (1g), 2-(6-methoxyanthr-2-yl)-pyridine (1h), and N-cyclohexylanthracene-2-carboxamide (1i) were investigated. In contrast to anthracene (1a), 1b, and 1c, the 2-methoxy-substituted anthracene derivatives 1d-1h exhibit two emission lifetimes. The determination of the lifetimes at different emission wavelengths and additional time-resolved emission spectroscopy (TRES) reveal that the dual emission originates from two different, interconvertible emissive species, with the s-cis and s-trans conformation relative to the exocyclic C2-O bond. The energy difference between the two emissive species is very small (0.1 eV) both in the ground and in the excited state. The larger energy difference between the conformers in the excited-state is responsible for the interconversion within the singlet excited-state lifetimes of the s-cis into the s-trans conformations leading to coupled decay kinetics. The proposed mechanism for the dual emission was qualitatively supported by theoretical studies on CASSCF and DFT level. In addition, the emission lifetimes of the fluoride- and pH-sensitive fluorescent probes 1f and 1g change upon addition of fluoride or acid, respectively, so that in these cases the detection of the fluorescence lifetime may be used complementary to the steady-state fluorimetric detection of these analytes.

The absorption and steady-state emission properties of a series of N-alkyl- and N-aryl-9-aminoacridizinium derivatives and two 9-sulfanyl-substituted acridizinium derivatives were investigated. The N-alkyl derivatives and the 9-methylsulfanylacridizinium have an intense intrinsic fluorescence (phi(f) = 0.2-0.6), whereas the N-aryl-substituted compounds are virtually nonfluorescent in liquid solutions (phi(f) < or = 0.01). The emission intensity of the latter compounds significantly increases with increasing viscosity of the medium. It is demonstrated that the excited-state deactivation of the N-aryl-9-aminoacridizinium derivatives is due to two nonradiative processes: (i) torsional relaxation by rotation about the N-aryl bond and (ii) an electron-transfer process from an electron-donor substituted phenyl ring to the photoexcited acridizinium chromophore. The binding of several representative acridizinium derivatives to double-stranded DNA was studied by the spectrophotometric titrations and linear dichroism spectroscopy. The results give evidence that the prevailing binding mode is intercalation with binding constants in the range (0.5-5.0) x 10(5) M(-1) (in base pairs). Notably, the binding of most of the N-aryl-9-aminoacridizinium derivatives leads to a fluorescence enhancement by a factor of up to 50 upon binding to the biomacromolecules. Moreover, the addition of selected proteins, namely albumins, to N-(halogenophenyl)-9-aminoacridizinium ions in the presence of an anionic surfactant (sodium dodecyl sulfate) results in a 20-fold fluorescence enhancement. In each case, the emission enhancement is supposed to result from the hindrance of the torsional relaxation in the corresponding binding site of the biomacromolecule, which in turn suppresses the excited-state deactivation pathway.

An improved preparation of 1,7-dimethylnaphthalene is presented, which is used as a precursor for the synthesis ofdiazoniahexacyclic salts, namely, 4a,14a-diazoniaanthra[1,2-a]anthracene (3) and 13a,16a-diazoniahexaphene (7). The influence of the reaction conditions on the formation of these isomers was investigated. Notably, the selectivity of the reactions depends significantly on the acid employed in the cyclization step. Both compounds exhibit similar absorption and fluorescence emission properties. Compound 3 exhibits a remarkable photopersistence in the solid state and in air-saturated aqueous solutions. However, diazoniahexaphene 7 undergoes rapid photodegradation in solution. X-ray diffraction analysis reveals that compound 3 adopts a helicene structure in the crystalline state.

The emission properties of selected benzo[b]quinolizinium (acridizinium) derivatives in the presence of double-stranded DNA and proteins are presented. Spectrophotometric studies and linear dichroism (LD) spectroscopic experiments reveal that benzo[b]quinolizinium derivatives bind to DNA, mainly by intercalation. In contrast to the 9-aminobenzo[b]quinolizinium, which exhibits a moderate emission quantum yield in water, the 6-aminobenzo[b]quinolizinium ion as well as N-phenyl-9-aminobenzo[b]quinolizinium derivatives are almost nonfluorescent. The low intrinsic fluorescence quantum yields of the latter compounds are caused by conformational changes in the excited state, as shown by a linear double-logarithmic plot of the emission quantum yield vs. the solvent viscosity. Most notably, the fluorescence intensities of these dyes increase significantly by a factor of 10 to 50 upon addition of double-stranded DNA or proteins such as human serum albumin (HSA) or chicken egg albumin (CEA). Thus, these compounds exhibit ideal properties to be used as DNA- or protein-sensitive light-up probes.

The cyclodehydration of bis(pyridiniummethyl)methylbenzenes 3a–b in polyphosphoric acid leads to methyl-substituted diazoniapentaphene salts 4a–b instead of linear diazoniapentacene derivatives, while the 1,3-bis(pyridiniummethyl)bromobenzene 3d forms a semi-betaine 4a,12a-diazoniapentaphen-14-olate 4d under these conditions. The mechanistic details of this rearrangement–cyclodehydration sequence may be explained by an intramolecular ipso-addition to the substituted benzene moiety, followed by an [1,2]-methyl shift in case of 4a–b or HBr elimination in case of 4d. The proposed mechanism was confirmed by the isolation of the intermediate hydroxy derivative 10b from the cyclization of 3a in refluxing HBr and conversion of 10b to the final product 4a by dehydration in polyphosphoric acid. Electronic absorption and fluorescence properties of the previously unknown diazoniapentaphene salts have been studied. Photophysical properties of 4a–b resemble the ones of the parent diazoniapentaphene salts, while semi-betaine 4d possesses a red-shifted absorption and fluorescence maxima, along with significant solvatochromism with respect to the absorption properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

DNA-binding properties of 15-crown-5-derived mono- and bis-styryl dyes were investigated in the presence of calf thymus DNA. To access the factors that influence the DNA association in the series of these ligands, the structure of the molecules was varied by either changing size of the heterocyclic moiety or altering the position of the styryl substituents. The major binding mode for the monostyryl dyes is intercalation. Notably, binding of the dyes to the nucleic acids leads to a fluorescence enhancement by a factor of up to 54. Therefore, these cationic styryl derivatives may be applied as fluorescent "light-up" probes for DNA detection.

The novel amino-substituted acridizinium salts 5 a and 5 b represent a new class of cyanine dyes which exhibit intense color along with efficient fluorescence properties. These dyes show moderate solvatochromism in their absorption and emission spectra. The absorption and emission shifts of the two chromophores display a reasonable correlation with solvent parameters such as donor and acceptor number. It was found that the dyes 5 a and 5 b interact with DNA, with quenching of the band intensies accompanied with a red shift of the absorption and emission bands. Moreover, irradiation of salts 5 a and 5 b in the presence of DNA results in DNA damage. Solution photolysis of acridizinium salt 5 a gave the head-to-tail dimers as the major products (>95 %), whereas the acridizinium salt 5 b afforded the anti-head-to-tail dimer along with both head-to-head isomers. The latter are thermally labile and rapidly revert to the monomer.

The novel 2,6-donor–acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.

The interactions of a triangle-shaped [2.2.2]heptamethinecyanine dye 1, namely 1,5,7-tris-[3-methylbenzothiazol-2-yl]-[2.2.2]heptamethindiium, with quadruplex DNA were studied with photometric and fluorimetric titrations, thermal DNA denaturation, CD and (1)H-NMR spectroscopy. The ligand binds to the quadruplex DNA with moderate affinity (K = 8 × 10(5) M(-1)), mainly by terminal π stacking. Remarkably, the ligand 1 exhibits a selectivity for quadruplex DNA relative to duplex DNA. Whereas the cyanine dye is very weakly fluorescent in aqueous solution, the emission intensity increases by a factor of100 upon association with quadruplex DNA. Thus, it is shown that trinuclear cyanine derivatives may be employed as selective probes for the fluorimetric detection of quadruplex DNA.

A comparative study of the ability of amino-substituted benzo[b]quinolizinium derivatives to act as DNA- or protein-sensitive fluorescent probes is presented. Spectrophotometric titrations, DNA denaturation studies and viscometric titrations showed that all tested aminobenzo[b]quinolizinium derivatives intercalate into DNA with binding constants K(b) = 10(4)-10(5) M(-1). The intense fluorescence of the 9-aminobenzo[b]quinolizinium (Φ(fl) = 0.41) as well as the intrinsically very weak emission of the 7-aminobenzo[b]quinolizinium (Φ(fl)0.005) are quenched by the addition of DNA, most likely caused by a photoinduced electron transfer (PET) between the excited intercalated ligand and the DNA bases. The 6-aminobenzo[b]quinolizinium (1b) and the 6-amino-9-bromobenzo[b]quinolizinium (1c) exhibit very low fluorescence intensity in water (Φ(fl)0.005). However, in water-glycerol mixtures the emission intensity increases by factors of 56 (1b) and 27 (1c) with increasing glycerol content of the solution (0-100 wt%), which indicates the radiationless deactivation of the excited state of 1b and 1c due to a torsional relaxation, i.e. rotation about the exocyclic C(ar)-NH(2) bond. In the case of the bromo-substituted derivative 1c, a viscosity-independent heavy-atom-effect of the bromo substituent leads to additional quenching. The association of 1b and 1c with ds DNA leads to a restricted conformational flexibility of the intercalated ligand and results in an increase of fluorescence intensity. This effect is particularly strong in the presence of poly[dA-dT]-poly[dA-dT]. Upon association with ct DNA or poly[dG-dC]-poly[dG-dC] only very small enhancement of emission intensity (1b) or even a slight quenching (1c) of the fluorescence was observed because of the interfering PET reaction with the guanine residues. Preliminary experiments reveal that the 6-aminobenzo[b]quinolizinium derivatives 1b and 1c may also be employed as protein-sensitive probes, because their emission intensity increases upon association with selected albumins.

The novel 2,6-donor–acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.

The arylation of readily available benzo(b)quinolizini- um-9-boronic acid with carbocyclic or heterocyclic bromoarenes in the presence of a palladium catalyst (Pd(dppf)Cl2·CH2Cl2 or Pd(PPh3)2Cl2) gives the corresponding cationic biaryl products in yields of 15-81%. All aryl-substituted benzo(b)quinolizinium (acridizinium) derivatives exhibit a long-wavelength absorption maximum between 409 and 422 nm in water, which change margin- ally in different solvents (Dl

[reaction: see text] The fluorescence properties of selected derivatives of 6-methoxyanthracene-2-carboxylic acid were studied. The corresponding ester and oxazoline derivatives exhibit a moderate solvatochromism, which is caused by the donor-acceptor interplay. The fluorescence band shift and intensity of oxazoline 1f may be reversibly modulated by protonation or complexation with silver ions; thus, the oxazoline heterocycle serves as a useful substituent with switchable acceptor strength.

The arylation of readily available benzo(b)quinolizini- um-9-boronic acid with carbocyclic or heterocyclic bromoarenes in the presence of a palladium catalyst (Pd(dppf)Cl2·CH2Cl2 or Pd(PPh3)2Cl2) gives the corresponding cationic biaryl products in yields of 15-81%. All aryl-substituted benzo(b)quinolizinium (acridizinium) derivatives exhibit a long-wavelength absorption maximum between 409 and 422 nm in water, which change margin- ally in different solvents (Dl

The integration of a selective Hg2+receptor unit, 1,4-dioxa-7,13-dithia-10-azacyclopentadecane, into the 9-aminoacridizinium fluorophore provides a fluorescent probe which allows a selective ratiometric detection of Hg2+ in water.

The acridizinium fluorophore was employed as water-soluble substitute for anthracene in PET probes and donor-pi-acceptor systems that may be used as fluorescent light-up probes and ratiometric probes in aqueous media.

The title compound exhibits a selective enhancement of its fluorescence intensity in the presence of AT-rich DNA.

The readily available cationic dye 3-Br binds to DNA as was shown by UV, fluorescence and CD spectroscopy. The electronic spectra of the quinolizinium salt 3 exhibit significant bathochromic shifts and a decrease of the absorbance and emission intensity on addition of calf thymus DNA. Moreover, fluorometric titration of [poly(dCdG)]2 with salt 3 resulted in a significant decrease of the emission intensity, whereas addition of [poly(dAdT)]2 led only to a marginal perturbation of the emission spectrum. Analysis of the binding constants with the different polynucleotides revealed that quinolizinium 3-Br binds preferentially to GC base pairs. Irradiation of DNA in the presence of quinolizinium 3-Br resulted in efficient single-strand cleavage of the nucleic acid.

N,N'-Dicyclohexyl-N-(6'-methoxyanthryl-2-carbonyl)urea (1a) exhibits a strong solvatochromism with respect to its fluorescence properties. The emission maxima of 1a correlate well with the anion-stabilizing properties of the solvent. This feature allows the detection of analytes with high acceptor numbers, such as alcohols and carboxylic acids, and the detection of analytes such as fluoride ions which form strong hydrogen bonds with the amido hydrogen atom.

An N-methylphenanthrolinium-annelated spirooxazine derivative 2(SO) whose DNA-intercalating properties are reversibly changed by a photochromic reaction was prepared. Upon irradiation at 350 nm the spirooxazine is transformed to the corresponding photomerocyanine 2(PM) that binds to DNA. After irradiation with visible light the spirooxazine 2(SO), which exhibits no significant DNA-binding properties, is regained. The association of 2(PM) with DNA was examined by CD and absorption spectroscopy, fluorescent intercalator displacement and viscometric titration.

A benzo[b]quinolizinium-benzo-15-crown-5 ether conjugate 2a is presented that enables the fluorimetric detection of Mg(2+) and DNA by a significant light-up effect, along with a change of the emission wavelength with different analytes (Mg(2+): 495 nm; DNA: 550 nm). The mechanism of the excited-state deactivation of 2a was investigated by steady-state fluorescence spectroscopy in media of varied viscosity and compared with the photophysical properties of methoxyphenyl-substituted benzo[b]quinolizinium 2b (m,p-diOMe), 2c (m-OMe), and 2d (p-OMe) as reference compounds. Compounds 2a-c, which share the m-alkoxyphenyl substituent as the common feature, have low emission quantum yields (Φ(F)10(-2) in water) but exhibit a significant increase of their fluorescence intensity in viscous glycerol solutions. In contrast, the viscosity of the medium does not influence the emission properties of the parent phenyl-substituted benzo[b]quinolizinium 2e and of the p-methoxyphenyl-substituted derivative 2d. Based on these observations it is concluded that the excited-state deactivation in 2a-c is mainly due to the rotation of the m-alkoxy group about the C(ar)-O bond. The interaction of 2a-c with DNA or Mg(2+) ions was studied by spectrophotometric titrations and CD spectroscopy. Notably, the association of 2a or 2b with DNA or 2a with Mg(2+) ions induces a strong fluorescence enhancement (15- and 40-fold for DNA, 450-fold for Mg(2+)), which is rationalized by the suppression of the torsional-relaxation of the alkoxy-substituent in the excited state. Additionally, the cation-induced light-up effect of 2a is selective towards Mg(2+) ions as compared with other cations such as NH(4)(+), Li(+), Na(+), K(+) and Ba(2+).

The integration of a selective Hg2+ receptor unit, 1,4-dioxa-7,13-dithia-10-azacyclopentadecane, into the 9-aminoacridizinium fluorophore provides a fluorescent probe which allows a selective ratiometric detection of Hg2+ in water.