Anion-lnduced Fluorescence Quenching of a New Zwitterionic Biacridine Derivative

The effect of halides and different buffer anions on the quenching of the fluorescence of the new probe 10,10′-bis(3-sulfopropyl)-9,9′-biacridine (SPBA) has been studied using fluorescence and decay time measurements. The linearity of the Stern-Volmer plot indicates that fluorescence quenching by halides can be described reasonably well by a single-exponential decay with a K of 4.06 times 10⁶M^-1s^-1for chloride, 7.83 times 10⁶M^-1s^-1for bromide and 1.12 times 10⁷M^-1s^-1for iodide. We have found that SPBA is collisionally quenched also by the buffers 3-(N-mor-pholino)propanesulfonic acid (MOPS) and N-2-hydroxy-ethylpiperazine-N′-ethansulfonic acid (HEPES). The bi-molecular rate constants are 1.67 × 10⁶M^-ls^-1for HEPES and 1.44 times 10⁶M^-1s^-1for MOPS.     

Chemistry of singlet oxygen. XVIII. Rates of reaction and quenching of alpha-tocopherol and singlet oxygen

Abstract —α-Tocopherol scavenges singlet oxygen (produced by methylene blue photosensitization in methanol) by a combination of chemical reaction (4.6 times 10⁷M^-1s^-1) and quenching (6.2 times 10⁸M^-1 s^-1). The total rate of scavenging (6.7 times 10⁸ M^-1s^-1) makes it an effective protective agent against photooxidation mediated by singlet oxygen.     

Photooxidation of Troglitazone,a New Antidiabetic Drug *

Troglitazone (CS-045) is a new oral antidiabetic drug reported to be effective in insulin-resistant diabetes and to show antihypertensive effects. Photooxidation of troglitazone gave the quinone and quinone epoxide as the major final stable products. An intermediate observed by NMR spectroscopy was shown to be the hydroperoxydi-enone, which is moderately stable at room temperature. The rate constant of singlet oxygen quenching by troglitazone is 2.14 × 10⁸M^?1s^?1 and the reaction rate constant in acetone-d, is 8.64 × 10, M^?1 s^?1. Only the chroman ring of troglitazone reacts with and quenches singlet oxygen significantly, and its reactivity and products are analogous to those of a-tocopherol. The reactivity of CS-045 toward singlet oxygen is much larger than that of the related compounds lacking the chroman ring.     

COMPLEX FORMATION BETWEEN PYRENE AND THE NUCLEOTIDES GMP, CMP, TMP AND AMP

Pyrene has been found to form ground and excited electronic state complexes of 1:1 stoichi-ometry with GMP, CMP, TMP and AMP. The values of their ground state association constants are 45 M^-1, 13M^-1, 14 M^-1, and 52 M^-1 respectively. The fluorescence of pyrene is strongly quenched by GMP, CMP, and TMP but only slightly by AMP. Fluorescence quenching analysis has yielded the values 87M^-1, 73 M^-1, and 154 M^-1 for the excited state association constants with GMP, CMP, and TMP, respectively. The corresponding values for the excited state second-order rate constant for complex formation are: 3.3 times 10⁹M^-1 s^-1 4.1 times 10⁹M^-1 s^-1, and 4.0 times 10⁹M^-1 s^-1. The probabilities of complex formation per collision between an excited pyrene molecule and a nucleotide are: 0.52, 0.64, and 0.63. The values for the excited state rate constant for dissociation of the complex are: 3.8 times 10⁷s^-1 5.6 times 10⁷s^-1, and 2.6 times 10⁷s^-1. The possibility is discussed that partial transfer of charge from pyrene to nucleotide may be playing a role in the complex formation process.     

MECHANISM OF THE PHOTOSENSITIZED REDOX REACTIONS OF ACRIDINE ORANGE IN AQUEOUS SOLUTIONS-A SYSTEM OF INTEREST IN THE PHOTOCHEMICAL STORAGE OF SOLAR ENERGY†

-We have carried out a very detailed study, using fluorescence and optical flash photolysis techniques, of the photoreduction of methyl viologen (MV²⁺) by the electron donor ethylene diamine tetraacetic acid (EDTA) in aqueous solution sensitized by the dye acridine orange (AOH⁺). A complete mechanism has been proposed which accounts for virtually all of the known observations on this reaction. This reaction is novel in that both the triplet and the singlet state of AOH⁺ appear to be active photochemically. We have shown that mechanisms previously proposed for this reaction are probably incorrect due to an artifact. At pH 7 the fluorescence quantum yield φ_s of AOH⁺ is 0.26 ± 0.02 and the fluorescence lifetime is 1.8 ± 0.2 ns. φ_s is pH dependent and reaches a maximum of 0.56 at pH 4. The fluorescence of AOH⁺ is quenched by MV²⁺ at concentrations above 1 mM and the quenching obeys Stern-Volmer kinetics with a quenching rate constant of (1.0 ± 0.1) × 10¹⁰M^?1 s^?1. The quenching of the AOH⁺ excited singlet state by MV²⁺ almost certainly returns the AOH⁺ to its ground state with no photochemistry occurring. EDTA also quenches the fluorescence of AOH· with Stern-Volmer kinetics but with a smaller rate constant (6.4 ± 0.5) × 10⁸M^?1s^?1 at pH 7. In this case the quenching is reactive resulting in the formation of semireduced AOH. In the presence of MV²⁺, flash irradiation of AOH⁺ does result in the reversible formation of the semireduced MV? which absorbs at 603 nm. We attribute this to a photochemical reaction of the triplet state of AOH⁺ with MV²⁺. The initial quantum yield for formation of MV? (φ_MV:)₀ was found to be constant at 0.10 ± 0.05 for [MV²⁺] from 5 × 10^?5 to 1.0 × 10^?3 with [AOH⁺] = 8 × 10^?6M. Previous workers had found that (φ_MV:)₀ appears to decrease with decreasing [AOH⁺]; however, on careful investigation, we found this was most probably due to quenching of the triplet state of AOH⁺ by trace amounts of oxygen. When EDTA is added to a mixture of AOH ⁺ and MV²⁺ at pH 7, the photochemical formation of MV? becomes irreversible as the [EDTA] is increased. The quantum yield for the irreversible formation of MV? exceeds 0.10 becoming as large as 0.16 for [EDTA] = 0.014M. This fact requires that an alternative photochemical process must be operative and we present evidence that this is a reaction of EDTA with the excited singlet state of AOH⁺ to produce the semi-reduced AOH- which then reacts with MV²⁺ to produce MV?. The full kinetic scheme was tested by computer simulation and found to be totally consistent. This also enabled the processing of a full set of rate constants. When colloidal PtO₂ was added to the optimal mixture [EDTA] = 3.4 × 10^?2M; [MV²⁺] = 5 × 10^?4M; [AOH⁺] = 4 × 10^?5M; pH6 H₂ gas was produced at a rate of 0.2μmol H₂h^?1. Thus, acridine orange should serve as an effective sensitizer in reactions designed to use solar energy to photolyze water.     

Efficiency and excited state processes in a three-component system,based on thioxanthene derived dye/amine/additive,usable in photopolymer plates

The excited state interactions occurring when a three-component system of thioxanthene derived dye TXD/amine/additive (diphenyliodonium salt, CBr₄, benzoyl peroxide, cumene hydroperoxide) is subjected to sensitization processes in the visible range, were investigated through time-resolved absorption spectroscopy, spectrofluorometry, and photolysis. The rate constants of the various operative processes were measured together with the values of the fluorescence quantum yields (e.g. ϕ _f = 0.75 ± 0.07 in methanol) and the lifetimes of the singlet excited state of the dye (e.g. 6 ns in methanol). Singlet state quenching by methyldiethanolamine (MDEA) occurs with a rate constant k = 10⁹ M⁻¹ s⁻¹ in methanol. The reactivity of the triplet excited state of the dye is very low (k = 5.6 × 10⁴ M⁻¹s⁻¹ for the TXD/MDEA interaction). The ketyl radicals that arise from the interaction of the singlet state of the dye with the amine, are quenched by such additives as CBr₄ (k = 6.7 × 10⁵M⁻¹s⁻¹), or the onium salts (k = 5.7 × 10⁵M⁻¹ s⁻¹). The calculations of the yields of interaction of the singlet state of the dye with the two components of the system demonstrate that the process of quenching by the amine is the main one (ϕ_int = 0.5) compared to that by, e.g., an onium salt (ϕ_int = 0.07). Sensitivity of 0.3 mJ cm⁻² obtained in a laser scanning system is also reported. © 1996 John Wiley & Sons, Inc.     

Reactivity of Singlet Oxygen Toward Proteins: The Effect of Structure in Basic Pancreatic Trypsin Inhibitor and in Ribonuclease A

The reactions of singlet oxygen, ¹O₂, with large peptides have been described previously. It was found that even in these systems, which in their native form are generally not supposed to possess a stable structure in solution, the polypeptide does impede the access of ¹O₂ to the amino acids that react readily with ¹O₂. Here we describe the ¹0₂ reaction with two proteins of well-defined structure. The quenching of ¹O₂ by bovine pancreatic trypsin inhibitor (BPTI) and by ribonuclease A (RNase A) was compared to that of a solution at the same concentration as those of its constituent amino acids that react readily with ¹O₂. The proteins were studied in their native form, when partly denatured by splitting their S-S bonds and when fully denatured. It was found that while in the native form the quenching rate constant was seven times lower in BPTI (2.2 vs 15.2 times 10⁷WM^-1 s^-1) and three times lower in RNase A (11.0 vs 32 times 10⁷M^-l s^-1) than in a mixture of its constituent amino acid residues, it increased upon denaturation reaching in the fully denatured state the value of the corresponding amino acid mixture. More striking is the effect of the protein structure when comparing the fraction of the encounters between ¹O₂ and protein, which cause damage to the protein, as reflected in the decrease of its biological activity. This decrease is assumed to be due to the chemical (oxidative) reactions of ¹O₂ in the protein. In the exceptionally stable BPTI the fraction of such encounters was 0.05 and in RNase A it was 0.2, whereas for the amino acid tryptophan in solution, 0.7 of the collisions with ¹O₂ led to a chemical reaction.     

DETERMINATION OF THE ACRYLAMIDE QUENCHING CONSTANT FOR PROTEIN AND MODEL INDOLE TRIPLETS

Abstract— The decay of the indole triplet of single tryptophan-containing proteins and model compounds can be readily measured at room temperature in aqueous solution by monitoring the triplet-triplet absorption or phosphorescence emission following a 265 nm exciting laser pulse. The quenching action of acrylamide on the triplet excited state of indole side chains was studied in an analogous fashion to that previously done at the singlet level (Eftink and Ghiron, 1977). The acrylamide triplet quenching constant (^tk_q) ranged from a high of 7.8 times 10⁸M^-1 s^-1 for the exterior indole of corticotropin (ACTH) to a low of 2 times 10⁵ Af^-1 s^-1 for the interior indole of ribonuclease T, (RNase T,). The ratio (7) of these values with their respective acrylamide singlet quenching constants (^tk_q),(γ=^tk_q⁸K_q) ranged from a high of 0.22 for ACTH to a low of 0.001 for RNase T₁,. Acrylamide is also an inefficient quencher of model indoles in various solvents (i.e. it has a γ less than 1). The magnitude of γ varied from a high of 0.3 in H₂0 to a low of 0.02 in acetonitrile, but did not correlate with viscosity, dielectric constant or polarity. The lower efficiency observed for internal indole groups can not be explained by that class of models which predict the presence of static quenching at the triplet level, since none was observed. The present results confirm the observation of Calhoun et al. of a large discrepancy between acrylamide's singlet and triplet quenching constants for buried indole side chains, but suggest that it may be largely explained by the fact that acrylamide is an inefficient quencher of the indole triplet state (1983). The magnitude of this inefficiency is probably determined by specific microenvironmental factors. Thus, unlike ⁸K_q, the environmentally sensitive ^lk_H cannot be easily used to characterize the dynamics of proteins.     

Amino acid-pyrrole N-conjugates; a new class of antioxidants II. Effectiveness of singlet oxygen quenching by luminescence measurements

The pyrrole-amino acid and peptide N-conjugates synthesized from tyrosine, histidine and glutathione very effectively quench the 1270 nm singlet oxygen luminescence, at rates ranging from 10⁸ to 10⁹ M⁻¹ s⁻¹. Nuclear magnetic resonance spectroscopy suggests that the electron-donating properties of the methyl groups after 2,5-dimethyl substitution on the pyrrole ring are probably an important determinant of the reactivity of singlet oxygen with the N-conjugate of glutathione. However, intramolecular interactions between the pyrrole ring and the side chain may also modulate the reactivity of the antioxidant as suggested by absorption and fluorescence spectroscopies carried out on tyrosine derivatives. Efficient fluorescence quenching of the phenol ring by the pyrrole ring occurs in the tyrosine derivatives. The reactivities of these antioxidants with ¹O₂ are comparable in methanol, ethanol and D₂O.     

CHARACTERIZATION OF THE RED LIGHT INDUCED REDUCTION OF A PARTICLE ASSOCIATED b-TYPE CYTOCHROME FROM CORN IN THE PRESENCE OF METHYLENE BLUE*

Methylene blue transfers electrons to a membrane-associated b-type cytochrome in particulate fractions from corn coleoptiles. The K_m for methylene blue is less than 1 µM under optimal conditions. This reaction is destroyed by boiling, but not by 7 M urea. Kinetic analyses of the influence of light intensity on cytochrome reduction suggest that a first order photochemical reaction is limiting. Free EDTA may serve as an electron donor in this system at least at high methylene blue and protein concentrations. The photoactivity does not coincide either with mitochondrial or endoplasmic reticulum markers, and may be localized in plasma membrane. There is an estimated 5 times 10^-10 mol photoreducible cytochrome per g coleoptile tissue. Studies on the effect of pH on the reaction in the presence of methylene blue or thionine indicate that dye photoreduction itself is not rate-limiting. Wavelength dependence studies suggest that it is methylene blue monomer and not dimer which mediates the reaction. Although oxygen is apparently required for the reaction, neither superoxide nor excited singlet oxygen appear to be involved. The reaction mechanism is still unknown.     

The fluorescence quenching of 1,4-bis[2-(5-phenyl-oxazolyl)]-benzene by bromomethanes

The interaction between the ground and excited states of 1,4-bis[2-(5-phenyloxazolyl)]-benzene and bromomethanes such as CBr₄, CHBr₃ and CH₂Br₂ were investigated in benzene. Distinct complex formation was not observed either in the ground state or in the excited states. The excited singlet and triplet states are deactivated by these bromomethanes. The triplet yield is increased on the addition of CHBr₃ or CH₂Br₂, whereas it is decreased on the addition of CBr₄. The fluorescence quenching rate constants k_q at 23 °C were determined to be 1.6 × 10¹⁰ M⁻¹ s⁻¹, 3.6 × 10⁸M⁻¹s⁻¹ and 2.4 × 10⁷M⁻¹s⁻¹ for CBr₄, CHBr₃ and CH₂Br₂ respectively. The rate constants k_ST′ of the enhanced intersystem crossing associated with the fluorescence quenching were evaluated from emission—absorption flash photolysis experiments as 3.0 × 10⁸ M⁻¹s⁻¹, 1.9 × 10⁸ M⁻¹s⁻¹ and 5.1 × 10⁷ M⁻¹s⁻¹ for CBr₄, CHBr₃ and CH₂Br₂ respectively. k_ST′ increases with increasing number of bromine atoms contained in the quencher, so that the enhanced intersystem crossing is due to the external heavy-atom effect of the quencher. The apparent triplet yield for the quenching system depends not only on k_ST′ but also on the rates of the other non-radiative processes. This is the reason why the apparent triplet yield does not necessarily increase on fluorescence quenching by bromomethanes.     

Sensitized photo-redox reaction: VII. The Synthesis,FAB mass spectrum,stationary absorption,emission, transient absorption spectra,redox potential of dihydroxy-tin (IV)-mesoporphyrin dimethyl ester and its sensitized photo-reduction of methyl viologen

In DMSO/water (4:1), photolysis of the dihydroxy-Sn (IV)-mesoporphyrin dimethyl ester (SnP)/methyl viologen (MV²⁺)/ethylene diamine tetraacetic acid (EDTA) ternary system produces methyl viologen cation radical with a quantum yield of 0.67, much higher than that of systems with other metal complexes of mesoporphyrin dimethyl ester. Neither EDTA nor MV²⁺ quenches the stationary fluorescence of SnP, implying that the reaction does not take place at the singlet state. With flash photolysis we obtain the T-T absorption spectrum of SnP (λ_max 440 nm). By following the decay of this absorption, the triplet life time of SnP is estimated to be 41 μs. The life time is related to the concentration of either MV²⁺ or EDTA. Good linear relationships are obtained by plotting τ₀τ vs. the concentration of MV²⁺ or EDTA (Stern-Volmer plot), from which we determine the quenching constants: _kq(MV²⁺) =5.5 × 10⁷ mol^?1, s^?1; k_q (EDTA) =2.7 × 10⁷ mol^?1, s^?1. The data suggests that upon photolysis of the above ternary system, both oxidative quenching and reductive quenching of the triplet state of the sensitizer are occurring. From the measured phosphorescence spectrum (λ_max 704 nm) and the ground state redox, potentials (E^red_1/2?-0.84V, E^ox_1/2?+1.43 V, vs. Ag/AgCl, KCl (sat.)), we obtain the redox potential of triplet SnP to be E(P⁺/P*_T)?-0.33 V, E(P*_T+/P^?)?+0.92 V. Matching this data with the redox potential of MV²⁺ and EDTA, we establish the fact that during the photolysis of the SnP/MV²⁺/EDTA ternary system, both oxidative and reductive quenching are thermodynamically favorable processes. This is also the reason why the SnP sensitized reaction is much more efficient relative to other mesoporphyrin derivatives.     

On the syntheses and singlet oxygen reactivity of oxodipyrromethene models for bilirubin

Various oxodipyrromethenes with varying β-substituents have been synthesized and their reaction with singlet oxygen studied. The rates of chemical reactivity (k_R) and physical quenching (k_Q) of singlet oxygen by those substrates approach the diffusion threshold in both chloroform and methanol solvents, with k_Q generally larger than k_R in chloroform but of comparable magnitude in methanol. The range of (k_Q+k_R) values is 0.2–4.2 × 10₉ M^?1 s^?1.     

Quenching of the fluorescence of ditolyl aminoacridine solutions by tetrabromomethane

It has been shown that fluorescence quenching of 2,7-dimethyl-N,N-di-p-tolylacridine-9-amine (9-DTAA) solutions in hexane and acetone by tetrabromomethane (TBM) was dynamic in nature with the quenching rate constants of 1.5 × 10¹⁰ and 0.6 × 10¹⁰ M⁻¹s⁻¹, respectively. The difference in the constants was explained by the possibility of competition between the processes of the formation of solvation shell around the excited singlet 9-DTAA* molecule and the formation of the 9-DTAA*/TBM encounter complex.     

Eosin-sensitized photoreduction of benzil with 1-benzyl-1,4-dihydronicotinamide

The mechanism of eosin-sensitized photoreduction of benzil with 1-benzyl-1,4-dihydronicotinamide — a model compound of NAD(P)H and the behavior of the excited states of eosin have been investigated. The effect of anthracene as a diffusion-controlled quencher of the photoreaction indicates that both excited triplet state and an unquenchable excited singlet state of eosin participated in the sensitized photoreaction. From the Stern-Volmer plot of quantum yield vs. anthracene concentration, the triplet reaction rate constant has been calculated to be 0.78 × 10⁸ L M^?1S^?1 while the singlet reaction rate constant determined from quenching of eosin fluorescence by benzil is equal to 7.2 × 10⁹ L M^?1S^?1. The singlet and triplet quantum yields are also determined to be 0.09 and 0.18 respectively. Since both the singlet and triplet energies of eosin are lower than that of benzil, energy transfer sensitization is not feasible. It is proposed that electron transfer from the excited eosin to benzil is responsible for the initiation.     

THE PHOTOPHYSICS OF BONELLIN: A CHLORIN FOUND IN MARINE ANIMALS

The photophysical properties of bonellin, a free-base chlorin, were studied in ethanolic solution. For the singlet excited state the following data were determined: an energy level, E^B_S= 187 ± 2kJ mol^-1, a lifetime, τ_f= 6.3± 0.1ns at 298 K, and fluorescence quantum yields, φ_r= 0.07 ± 0.02 (298 K) and 0.20 ± 0.04 (77 K). The S₁→ T intersystem crossing quantum yield was φ_isc= 0.85 ± 0.1. No phosphorescence was observed at 298 K and 77 K. Based on quenching experiments the triplet state energy level was determined to be E^B_T= 180 ± 20 kJ mol^-1. A unimolecular decay rate constant, k₁= (2.3 ± 0.5)· 10³ s^-1 at room temperature, and a molar absorption coefficient, ε^T₄₄₃= 9500 ± 500 M^-1 cm^-1, were obtained for the triplet state. This species was quenched by O₂ with ko₂= (1.7 ±0.3)· 10⁸M^-1 s^-1, and by benzoquinone with k_q= (5.2 ± 0.3)-10⁹M^-1 s^-1. The latter value, as well as the high value determined for the triplet annihilation rate constant, k₂= (2 ± 0.5)· 10⁹M^-1 s^-1, might reflect an electron transfer mechanism. Copper bonellin had a shorter triplet lifetime (>20 ns), which offers a possible explanation for its lack of photodynamic action.     

CHLOROPHYLL PHOTOCHEMISTRY IN CONDENSED MEDIA—I. TRIPLET STATE QUENCHING AND ELECTRON TRANSFER TO QUINONE IN CELLULOSE ACETATE FILMS*

Chlorophyll-a was incorporated into cellulose acetate films and the triplet state decay kinetics and electron transfer from triplet to p-benzoquinone in aqueous solution was studied using laser flash photolysis and EPR. The triplet was found to decay by first order kinetics with a rate constant which was independent of Chl concentration. The triplet yield, however, was concentration dependent. These properties are due to quenching which occurs only at the singlet state level. In the presence of quinone, the triplet is quenched and, when the quinone is in an aqueous solution in contact with the film, Chl cation radical (C^±) as well as the semiquinone anion radical (Q^±) can be observed. The C decays by second order kinetics with a rate constant of 1.5 × 10⁶M^-1 s^-1. Although triplet conversion to radicals is slightly lower in the films as compared to fluid solutions (? 3 times), the lifetimes of the radicals are greatly increased (? 10³ times).     

Singlet excited-state “energy hopping” in alkylbenzenes

The quenching of toluene fluorescence by cis-6-phenyl-2-hexene has been studied to determine the rate of singlet “energy hopping” in dilute solutions of alkylbenzenes. The singlet lifetime date have been analyzed by the Stern-Volmer method to give the quasi-isoenergetic rate, k_q, as 1.2 × 10¹⁰ M^?1?1. The result is consistent with an excimer formation dissociation mechanism for alkylaromatic singlet energy transfer in dilute solution.     

Solvent effect and temperature dependence in the interaction of singlet oxygen with α-phenyl-N-tert-butyl nitrone

The solvent effect on the quenching of singlet oxygen by -phenyl-N-tert-butyl-nitrone /PBN/ has been investigated by laser flash photolysis technique registrating luminescence kinetics of¹O₂. The values of the rate constant /k_q/ of the quenching were at 293 K: /9.0±0.4/×10⁶, /4.4±0.3/×10⁶ and /18.3±0.5/×10^{6 –}M^–1 s^–1 in toluene, chloroform and acetonitrile, respectively. The rate constant for the chemical interaction between¹O₂ and PBN, was k_r<1×10⁵ M^–1 s^–1k_q independently of the solvent. At temperatures between 223 and 293 K in toluene E_q=0.4±0.4 kJ mol^–1.     

AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER–I. ELECTROSTATIC EFFECT ON THE FORWARD REACTION AS STUDIED BY FLUORESCENCE QUENCHING

Abstract— Fluorescence quenching of amphiphilic copolymers, poly(9-vinylphenanthrene-co-sodium 2-acrylamido-2-methylpropanesulfonate) (APh) and poly(9-vinylphenanthrene-co-3-methacrylamidopropyltrimethylammonium methyl sulfate) (QPh), in aqueous solution, was studied using methyl viologen (MV²⁺) or 4,4'-bipyridinium-1, 1'-bis(trimethylenesulfonate) (SPV) as oxidative quenchers. The fluorescence of the excited phenanthrene groups in APh was found to be efficiently quenched by MV²⁺. The apparent second-order rate constant for the quenching, k_q, ranged in the magnitude of 10¹¹ -10¹²M^-1 s^-1, which are well beyond the diffusion-controlled limit. This is presumably due to an increase of the effective concentration of MV²⁺ around the fluorophore in the copolymer resulting from electrostatic attraction between MV²⁺ and anionic segments of APh. This strong electrostatic interaction also favors the formation of ground-state EDA (electron donor acceptor) complex between the phenanthrene residue and MV²⁺. Such striking behaviors were not observed with the related model compound. Unexpectedly, the quenching with SPV, a zwitterionic quencher, was also enhanced in the polymer system (k_q= 2–6 × 10¹⁰M^-1 s^-1), suggesting the presence of some attractive interaction between APh and SPV. Contrary to the APh system, the fluorescence quenching of the corresponding cationic polymer (QPh) with MV²⁺ was strongly diminished (k_q= 5 × 10⁸M^-1 s^-1). This indicates that the polycation of QPh effectively prevents the access of MV²⁺ to the polymer.