Exciplex photophysics. 7. Steric effects in exciplex photophysics

Cheung, Seung Tong; Ware, William R.

doi:10.1021/j100226a019

Cited by 40 publications

(24 citation statements)

References 6 publications

(7 reference statements)

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“…We assume uncertainties of ∆F/F 0 ) 0.005 for POPOP quenched by bromoform, methyl iodide, potassium iodide, TMB, and DEA. D y(r)a,t) (12) [ ∂y(r,t) ∂r ] r)a ) 0 …”

Section: Appendix: Theorymentioning

confidence: 99%

Distance-Dependent Fluorescence Quenching ofp-Bis[2-(5-phenyloxazolyl)]benzene by Various Quenchers

et al. 1996

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We report results of frequency-domain and steady-state measurements of the fluorescence quenching of p-bis-[2-(5-phenyloxazolyl)]benzene (POPOP) when quenched by bromoform (CHBr 3 ), methyl iodide (CH 3 I), potassium iodide (KI), 1,2,4-trimethoxybenzene (TMB), or N,N-diethylaniline (DEA). The quenching efficiency of these compounds decreased in the order DEA, TMB, KI, CH 3 I, CHBr 3 . In the case of DEA and TMB the measurements clearly confirm the applicability of the exponential distance-dependent quenching (DDQ) model, in which the bimolecular quenching rate k(r) depends exponentially on the fluorophore-quencher separation r, k(r) ) k a exp[-(r -a)/r e ], where a is the distance of closest approach. Simultaneous analysis of the frequency-domain and steady-state data significantly improved resolution of the recovered molecular parameters k a and r e . The data for DEA and TMB cannot be satisfactorily fit using either the Smoluchowski or CollinsKimball radiation boundary condition (RBC) model. The quenching behavior of the less efficient quenchers KI, CH 3 I, and CHBr 3 can be adequately described with both the DDQ and RBC models, but this may be a simple consequence of less efficient quenching. The efficiency of quenching is discussed on the basis of the mechanisms of interaction between the fluorophore and quencher molecules, which involves electron transfer and/or heavy atom effects. IntroductionCollisional quenching of fluorescence has been widely used in physical chemistry and biochemistry. Fluorescence quenching of aromatic and heteroaromatic hydrocarbons by aromatic amines, 1-13 aromatic nitriles, 14 haloalkanes, 15-24 and halide ions 25-27 as well as by nitroxides 28,29 and oxygen 30,31 has been studied to determine the bimolecular rate constants, to characterize the solvent effects on quenching, and to determine the mechanisms of interaction between the fluorophore and quencher molecules. Moreover, collisional quenching of tryptophan fluorescence by a variety of ionic and neutral quenchers has been used to study the structure and dynamics of proteins 32-40 and membranes. 41,42 Collisional or dynamic quenching requires contact between the fluorophore and quencher molecules during the lifetime of the excited state. The quenching data can reveal information about accessibility of fluorophores in macromolecules to externally added quenchers and the diffusion of quenchers within proteins and membranes.For many fluorophores in solution, including aromatic and heteroaromatic fluorophores, the intensity decays are often monoexponential. 43 However, in the presence of collisional quenching the monoexponential intensity decays become nonexponential due to transient effects in diffusion. 21,[44][45][46] This effect in collisional quenching of fluorescence is due to a rapid decay of closely spaced fluorophore-quencher pairs, followed by slower diffusion-limited quenching of remaining fluorophores. These effects can be readily detected by using frequency-domain fluorometry. [47][48][49] We have shown for several fl...

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“…We assume uncertainties of ∆F/F 0 ) 0.005 for POPOP quenched by bromoform, methyl iodide, potassium iodide, TMB, and DEA. D y(r)a,t) (12) [ ∂y(r,t) ∂r ] r)a ) 0 …”

Section: Appendix: Theorymentioning

confidence: 99%

Distance-Dependent Fluorescence Quenching ofp-Bis[2-(5-phenyloxazolyl)]benzene by Various Quenchers

et al. 1996

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“…[1][2][3][4][5][6][7][8] The formation process, k 3 , is often believed to occur with a diffusion-controlled rate for some donor/acceptor systems. When the solute molecules diffuse together in a continuum medium with viscosity, η, the diffusioncontrolled rate constant, k diff , is given by where R is 3000 and 2000 for the stick and slip boundary limits, respectively, on the basis of the Stokes-Einstein equation.…”

Section: Introductionmentioning

confidence: 99%

Time-Resolved Fluorescence Study on the Pressure-Induced Viscosity Dependence of Exciplex Formation in Liquid Solution

Okamoto

2000

J. Phys. Chem. A

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The contribution of diffusion to the exciplex formation of the 1,2-benzanthracene (BZAN)/dimethylaniline (DMA) and pyrene (PY)/DMA systems in methycyclohexane at pressures up to 400 MPa was investigated. The rate constant, k 3 , for the exciplex formation, which was determined by the analysis of the rise and decay curve of the exciplex emission, decreased significantly with increasing pressure. The apparent activation volume for k 3 , ∆V 3 * , was 14.9 and 18.1 cm 3 /mol for BZAN/DMA and PY/DMA, respectively. For comparison, the rate constant, k q , for the fluorescence quenching by carbon tetrabromide (CBr 4 ) of BZAN and PY that is believed to be fully diffusion-controlled was also measured as a function of pressure. The apparent activation volume for k q , ∆V q * , was 17.9 and 20.1 cm 3 /mol for BZAN/CBr 4 and PY/CBr 4 , respectively. These results are interpreted by assuming an encounter complex formed between the donor and acceptor pairs, and it was concluded that the exciplex formation reaction studied in this work is not fully diffusion controlled but competes with a diffusion process of the donor and acceptor molecules that is expressed by a modified Debye equation. It was also concluded that the quenching by CBr 4 is not fully diffusion controlled at the lower pressure range. The bimolecular rate constant, k bim () k c k diff /k -diff ), for the exciplex formation was estimated to be 1.5 × 10 10 M -1 s -1 for BZAN/DMA and 1.9 × 10 10 M -1 s -1 for PY/DMA. The activation volumes for the various rate processes also are discussed.

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“…restrictions imposed by the anisotropic "liquid crystal" structure (Jain, 1988;Sackman, 1983) on the relative orientations of 'Py* and DEA during the quenching reaction. Thus, the exciplex yield, (t)e. = keXI (k,Ce + kip) due to a high effective polarity will be lowered by a low kex rather than by an increase in kip, The much higher sensitivity of ke,x as compared to kip, to the relative geometrical orientation of the reacting pair is indicated by several studies of intra-and intermolecular exciplex generation (see review by Mataga and Ottolenghi, 1979;Chuang et al, 1974;Mataga et al, 1976;Okada et al, 1977;Cheung and Ware, 1983;Yorozu et al, 1981;Avnir et al 1989). In analogy to such systems it is feasible that the lack of exciplex emission in the organized membrane medium may be attributed to restrictions imposed on the sandwich-type configurations required for excited complex formation as compared with less critical relative orientations of 'A * and D needed for the generation of the ion pair.…”

Section: Charge Recombination Processmentioning

confidence: 99%

Organization and dynamics of pyrene and pyrene lipids in intact lipid bilayers. Photo-induced charge transfer processes

Barenholz¹,

Cohen²,

Korenstein³

et al. 1991

Biophysical Journal

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The dynamics of fluorescence quenching and the organization of a series of pyrene derivatives anchored in various depths in bilayers of phosphatidylcholine small unilamellar vesicles was studied and compared with their behavior in homogeneous solvent systems. The studies include characterization of the environmental polarity of the pyrene fluorophore based on its vibronic peaks, as well as the interaction with three collisional quenchers: the two membrane-soluble quenchers, diethylaniline and bromobenzene, and the water soluble quencher potassium iodide. The system of diethylaniline-pyrene derivatives in the membrane of phosphatidylcholine vesicles was characterized in detail. The diethylaniline partition coefficient between the lipid bilayers and the buffer is approximately 5,800. Up to a diethylaniline/phospholipid mole ratio of 1:3 the perturbation to membrane structure is minimal so that all photophysical studies were performed below this mole ratio. The quenching reaction, in all cases, was shown to take place in the lipid bilayer interior and the relative quenching efficiencies of the various probe molecules was used to provide information on the distribution of both fluorescent probes and quencher molecules in the lipid bilayer. The quenching efficiency by diethylaniline in the lipid bilayer was found to be essentially independent on the length of the methylene chain of the pyrene moiety. These findings suggest that the quenching process, being a diffusion controlled reaction, is determined by the mobility of the diethylaniline quencher (with an effective diffusion coefficient D approximately 10(-7) cm2 s-1) which appears to be homogeneously distributed throughout the lipid bilayer. The pulsed laser photolysis products of the charge-transfer quenching reaction were examined. No exciplex (excited-complex) formation was observed and the yield of the separated radical ions was shown to be tenfold smaller than in homogenous polar solutions. The decay of the radical ions is considerably faster than the corresponding process in homogenous solutions. Relatively high intersystem crossing yields are observed. The results are explained on the basis of the intrinsic properties of a lipid bilayer, primarily, its rigid spatial organization. It is suggested that such properties favor ion-pair formation over exciplex generation. They also enhance primary geminate recombination of initially formed (solvent-shared) ion pairs. Triplet states are generated via secondary geminate recombination of ion pairs in the membrane interior. The results bear on the general mechanism of electron transfer processes in biomembranes.

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Exciplex photophysics. 7. Steric effects in exciplex photophysics

Cited by 40 publications

References 6 publications

Distance-Dependent Fluorescence Quenching ofp-Bis[2-(5-phenyloxazolyl)]benzene by Various Quenchers

Distance-Dependent Fluorescence Quenching ofp-Bis[2-(5-phenyloxazolyl)]benzene by Various Quenchers

Time-Resolved Fluorescence Study on the Pressure-Induced Viscosity Dependence of Exciplex Formation in Liquid Solution

Organization and dynamics of pyrene and pyrene lipids in intact lipid bilayers. Photo-induced charge transfer processes

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