The quenching of excited aromatic esters by triethylamine (original) (raw)
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Journal of Photochemistry, 1976
A study is made of the quenching of fluorescence of a number of aromatic compounds by triphenyl derivatives of group V elements and by triethylamine in both non-polar and polar solvents. Whilst quenching is observed in many cases, the lack of correlation of the quenching rate with the ionization potential of the quencher suggests that this does not simply involve electron or charge transfer. Evidence is presented that a heavy atom effect involving the group V element -is also important. Further, a search has been made for evidence of exciplex formation in the quenching of azulene Sa fluorescence by a variety of compounds. However, no new emissions attributable to such a species are observed under the conditions studied. In addition, in polar solvents there is no evidence for an overall electron-transfer reaction in the quenching suggesting that if an intermediate charge-transfer or ion pair state is formed this may be of higher energy than the lowest singlet or triplet state, and may decay to yield one of these levels. lidroduction Excited singlet states of a variety of aromatic compounds have been shown to interact with amines [ 1 ] , inorganic anions [Z] , organo-derivatives of lead, tin and mercury [ 31, and various other inorganic, organic and organic and organometallic derivatives, as indicated by the quenching of the hydrocarbon fluorescence. The quenching is generally attributed to charge-transfer *Present address: Davy Faraday Research Laboratory of the Royal Institution, 21, Albemarle Street, Londc+n WlX 4BS (Gt. Britain).
Intermolecular quenching of the second excited state of some aromatic molecules
Chemical Physics Letters, 1969
FIuorescence quenching of some polycyclic hydrocarbons in different solvents has been studied as a function of excitation wavelength. With most quenchers the Stern-Vobner quenching constant remafns fnsensitive to the wavelength of the irradiating beam. But when CC14 and CHCi3 are used as quenchers. the quenching constant obtained by populating the second excited state of the hydrocarbon is larger tbnn the corresponding value for the first excited state. However, excitation into the different vibrational sublevels of 2 particular electronic state does not affect the quenching constant. Quenching of the second excited state is ascribed to the formation of a solvated ion-pair.
The Journal of Physical Chemistry B, 2005
Steady-state absorption and emission spectra and emission decay kinetics are reported for 4-aminobenzonitrile (ABN), 4-(1-azetidinyl)benzonitrile (P4C), 4-(1-pyrrolidinyl)benzonitrile (P5C), and 4-(1-piperidinyl)benzonitrile (P6C) in 24 room temperature solvents. In solvents of modest to high polarity, P4C, P5C, and P6C exhibit dual fluorescence and emission decays characteristic of the transformation from an initially prepared (LE) state to a more polar charge transfer (CT) state, whereas ABN does not undergo this reaction. The frequencies of the steady-state absorption and emission spectra of all of these solutes can be rationalized using a dielectric continuum description of the solvent and considering only the minima on the reactive surfaces, which are assumed to involve both an intramolecular (twisting) and a solvation coordinate. Characteristics of the gas-phase solutes deduced from this analysis are in good agreement with electronic structure calculations and indicate that differences in their spectra mainly reflect differences in the relative energies of the gasphase LE and CT states. The relative yields of LE and CT emission are not described as satisfactorily by this model, and reasons for this failure are discussed. The kinetics of the LE f CT reaction vary considerably with solute and solvent. In many solvents, the emission decays of P4C are reasonably described by a simple two-state kinetic scheme with time-independent rate constants. In P5C and P6C multiexponential decays are observed that reflect time-dependent shifts of the component spectra as well as time-dependent reaction rates. A simplified analysis of these complex dynamics provides estimates for both the free energy change ∆ r G and (average) LE f CT rate constant k f for a wide range of solute and solvent combinations. The driving force for reaction (-∆ r G) follows the order P6C > P5C > P4C and increases with increasing solvent polarity. The reaction rates are correlated to ∆ r G and follow the opposite trend. The relationships observed between k f and ∆ r G suggest that static solvent effects, i.e., barrier height changes, are the primary determinants of the solvent dependence in P4C. Correlations between barrier-corrected rates and solvation times suggest that dynamical solvent effects contribute substantially to the solvent dependence of the rates in P5C, and especially P6C.
Chemical Physics Letters, 1995
Fluorescence quenching of anthracene derivatives by organic electron donors (amines) and acceptors was investigated using stationary fluorescence measurements. The dependence of log(kq) on AGet shows Rehm-Weller-type behavior. The formation of anion radicals of anthracene, bianthryl, and 9-cyanoanthracene was detected by flash photolysis in systems containing aromatic amines (aniline, 2-bromoaniline, 4-bromoaniline, N,N-dimethylaniline, 4-bromo-N,N-dimethylaniline, N,N-diethylaniline, and 1,4-diazabicyclo[2.2.2]octane). The radical yields decreased and triplet yields increased when bromo derivatives of amines were used as donor quenchers, indicating the heavy-atom effect on spin conversion within radical pairs. The importance of the heavy-atom effect decreased when the energy gap between the charge transfer and molecular triplet states was small. The formation of separated radicals decreased when primary amines were used as quenchers which indicated the existence of an additional path of deactivation of the radical pair. The behavior of amines as quenchers of bianthryl and anthracene is compared with that of inorganic anion quenchers. 0009-2614/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0009-2614(95)00145-X
Chemical Physics, 2008
The ground and excited state hydrogen bonding interactions between N2-methyl-9H-pyrido[3,4-b]indole, BCA, and 1,1,1,3,3,3-hexafluoropropan-2-ol, HFIP, are comparatively studied in the aprotic solvents cyclohexane and toluene by absorption, steady state and time resolved fluorescence measurements. The different photophysical behaviours of the BCA–HFIP hydrogen bond complexes in these solvents definitively confirm the existence of two ground state BCA isomers. As previously proposed [A. Sánchez-Coronilla, C. Carmona, M.A. Muñoz, M. Balón, Chem. Phys. 327 (2006) 70.] we assume quinoid, Q, and zwitterionic, Z, structures for these isomers. Upon excitation, the hydrogen bond adducts of each isomer give dual fluorescence emitting from their locally excited states, LE, and from their intramolecular charge transfer states, ICT. In the hydrogen bond adducts of the Q form, the ICT process is favoured while it is disfavoured for the corresponding adducts of the Z form. The implication that these results could have on the current mechanistic interpretation of the excited state intramolecular proton transfer and phototautomerism of the betacarbolines is discussed.
Journal of the American Chemical Society, 1977
Am. Chem. SOC., 91, 5090 (l969), (37) Although most evidence for the formation of trlpiet excipiexes and excimers is of an Indirect nature, Takemura and co-workers have now reported emission from triplet exclmers of naphthalene and 1-chloronaphthalene; T. Takemura, M. Alkawa, H. Baba, and Y. Shindo, J. Am. Chem. SOC., Q8, 2205 (1976). (38) Gupta and Hammond have recently reported quantum yield evidence which suggests that certain alkenes and acetophenone triplets form exciplexes which can be quenched by cis-piperylene: A. Gupta and 0. S. Hammond, Abstract: Measurements have been made of the fluorescence quantum yields (~F M ) , lifetimes, spectra, and of the photoisomerization quantum yields ( 4~) of trans-styrylnaphthalenes (StN's) in deaerated and aerated solutions of n-hexane and acetonitrile, and the effect of the addition of amines on these properties has been studied. The fluorescence quenching is associated with exciplex emission, and the Stern-Volmer quenching coefficient increases with a decrease in the amine ionization potential. @C is reduced proportionately less than ~F M , and in some cases it is increased, by the addition of the amine. Analysis of the data for P-StN + diethylaniline (DEA) in n-hexane provides extensive kinetic parameters which indicate that the photoisomerization occurs via the triplet state with a quantum efficiency q c T = 0.41, increased to qCT = 0.47 (fO.01) in the presence of DEA or oxygen. Similar results have been obtained for a-StN and 4-Br-a-StN. A model of the S I potential of 0-StN is proposed. H2SO4 as standard. A CGA DC-3000/1 spectrofluorimeter was also used. The solutions were deaerated by bubbling nitrogen. The Stern-Volmer (SV) fluorescence quenching coefficient K = ~Q M T M (M-I) was obtained from observations of the fluorescence quantum yield @FM as a function of the amine concentration [ Q ] .
The Journal of Physical Chemistry A, 2003
The electron transfer quenching dynamics of excited perylene and cyanoperylene in various donating solvents has been investigated by using ultrafast fluorescence up-conversion and multiplex transient grating. The strongly nonexponential fluorescence decays have been analyzed by using the orientational model described in the first article of this series (J. Phys. Chem. A 2003, 107, 5375). It appears that the solvent dependence of the quenching dynamics is strongly connected to the number of surrounding donor molecules enabling ultrafast electron transfer. This number depends mainly on the driving force for electron transfer, on steric interactions, and on the occurrence of dipole-dipole interactions with the acceptor. The quenching product is an exciplex with a strong charge-transfer character. The complicated wavelength dependence of the fluorescence dynamics in the exciplex region, as well as the spectral dynamics observed in the transient grating data, is attributed to dipolar solvation, which leads to an increase of the charge-transfer character of the exciplex. The strong donor dependence of the exciplex lifetime is very similar to that reported earlier for the charge recombination time of geminate ion pairs in acetonitrile, and can be rationalized in terms of different intramolecular reorganization energies and electronic coupling constants.
Excited state dynamics of 4(1H-pyrrole 1-yl) benzoic acid and different environmental effects
Journal of Photochemistry and Photobiology A: Chemistry, 1998
This paper describes the dual fluorescence of 4-N,N-dimethylamino cinnamaldehyde (DMACA) in various solvents. Based on major findings the first fluorescence band has been assigned to be arising out of delocalized excited state (DE) and the anomalous fluorescence band in polar aprotic solvents has been assigned to twisted intramolecular charge transfer (TICT) state whereas, in protic solvent it is arising out due to hydrogen bonding interaction between hydrogen donor part of the solvent and carbonyl group of the probe molecule. This hydrogen bonding being an efficient fluorescence quenching channel trammels the TICT formation and thus an apparent competition exists between TICT and hydrogen bonding formation in protic solvent. The calculated absorption spectrum generated from CNDO calculations follows nicely the experimental absorption band. The AM1 calculations corroborate the large dipole moment change and the charge transfer in orthogonal position as found from experimental observations.
Interaction of the Excited Singlet State of Neutral Red with Aromatic Amines
Photochemistry and Photobiology, 2000
Quenching of neutral red (NR; neutral form of the dye) fluorescence by a number of aromatic amines has been investigated in acetonitrile solutions. The bimolecular quenching constants (k q) obtained from steady-state and time-resolved measurements for a particular donor-acceptor pair are seen to be the same within experimental error. Correlation of the changes in the k q values with the oxidation potentials of the donors (amines) indicates that electron transfer (ET) is the mechanism operative in the present systems. Direct evidence for ET has been obtained from picosecond transient absorption studies on a suitable amine-NR pair. Experimentally determined k q values are seen to correlate well with the free energy changes (⌬G 0) for the ET reactions, within the framework of the Marcus outer sphere ET theory. From the correlation between the experimentally determined and theoretically calculated k q values, it appears that solvent reorganization plays a major role in governing ET dynamics in the systems investigated.
The fluorescence quenching studies of carboxamide namely (E)-N-(3-Chlorophenyl)-2-(3,4-dimethoxybenzylideneamino)- 4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxamide [ENCDTTC] by aniline and carbon tetrachloride in six different solvents namely toluene, cyclohexane, n-hexane, n-heptane, n-decane and n-pentane have been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S–V) plots have been found to be nonlinear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximationmodel, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes Einstein relation.