“…The function derived from this model indicates that the rate constant for the quenching reaction is time dependent, resulting in a decay of the excited species that is nonexponential.41 •42 The deviation from exponentiality for the decay of the excited singlet state or the excited triplet state for all of the anthracene derivatives examined in this work was undetectably small in aerated solution. 53 In this limit, the expression for the rate constant associated with the quenching reaction, fcq (kq or fcq), is53 kq = 4 vR'DN AirRDNk " = *act + AirRDN (26) where the value for fcact also includes the spin-statistical factor.7* The viscosity-dependent parameter in this expression, D, which is often considered to be inversely proportional to ,53 appears in both the numerator and the denominator. Consequently, the overall viscosity dependence of fcq may well appear to be equivalent to that given by eq 2 in which the magnitude of a is less than unit.…”
The effect of solvent viscosity on the quenching by oxygen of S1 and T1 states was investigated for a number of meso-substituted anthracene derivatives. The solvent viscosity, r], was varied by applying hydrostatic pressure at several temperatures. The fluorescence from the S1 state of the anthracene derivatives that have one or two electron-donating substituents was quenched nearly collisionally, and the dependence of the rate constant for fluorescence quenching, kS, on r] was shown to be described satisfactorily by the empirical function, Aq". It was shown for 9-methylanhracene in methylcyclohexane that the exponent, a, has a value of 0.68 f 0.06, which is independent of temperature and pressure but that thevalue of the constant of proportionality, A, is temperature dependent. The dependence of A on temperature was described empirically using the functions P.36 or exp(-AEIRT). An alternative function for is (T/r])@, but this function failed to describe correctly the dependence of kt on 9 and T. The fractional power dependence of k: on 4 suggests that the rate constant for the intrinsic fluorescence quenching reaction, kaCt, is not significantly larger than the rate constant for diffusion.The values of k: for the anthracene derivatives containing one or two electron-attracting substituents were smaller than that found for anthracene, decreased with Hammett's up parameter, and could not be described by the empirical function A?* with a constant value for a. A typical example is 9,lO-dicyanoanthracene whose values for k: exhibit a convex dependence on In r]. In accordance with this, the activation energy associated with k: was negative at low viscosities and displayed a transition from negative to positive values as the viscosity was increased. The values of the rate constant for the quenching by oxygen of the T1 states of the anthracene derivatives, k t , did not vary significantly, all being approximately 3 X lo9 M-1 s-l at 25 OC and 0.1 MPa. The logarithmic values of k;, when plotted as a function of In r], displayed appreciable downward curvature for all of the anthracene derivatives examined in this work.
“…The function derived from this model indicates that the rate constant for the quenching reaction is time dependent, resulting in a decay of the excited species that is nonexponential.41 •42 The deviation from exponentiality for the decay of the excited singlet state or the excited triplet state for all of the anthracene derivatives examined in this work was undetectably small in aerated solution. 53 In this limit, the expression for the rate constant associated with the quenching reaction, fcq (kq or fcq), is53 kq = 4 vR'DN AirRDNk " = *act + AirRDN (26) where the value for fcact also includes the spin-statistical factor.7* The viscosity-dependent parameter in this expression, D, which is often considered to be inversely proportional to ,53 appears in both the numerator and the denominator. Consequently, the overall viscosity dependence of fcq may well appear to be equivalent to that given by eq 2 in which the magnitude of a is less than unit.…”
The effect of solvent viscosity on the quenching by oxygen of S1 and T1 states was investigated for a number of meso-substituted anthracene derivatives. The solvent viscosity, r], was varied by applying hydrostatic pressure at several temperatures. The fluorescence from the S1 state of the anthracene derivatives that have one or two electron-donating substituents was quenched nearly collisionally, and the dependence of the rate constant for fluorescence quenching, kS, on r] was shown to be described satisfactorily by the empirical function, Aq". It was shown for 9-methylanhracene in methylcyclohexane that the exponent, a, has a value of 0.68 f 0.06, which is independent of temperature and pressure but that thevalue of the constant of proportionality, A, is temperature dependent. The dependence of A on temperature was described empirically using the functions P.36 or exp(-AEIRT). An alternative function for is (T/r])@, but this function failed to describe correctly the dependence of kt on 9 and T. The fractional power dependence of k: on 4 suggests that the rate constant for the intrinsic fluorescence quenching reaction, kaCt, is not significantly larger than the rate constant for diffusion.The values of k: for the anthracene derivatives containing one or two electron-attracting substituents were smaller than that found for anthracene, decreased with Hammett's up parameter, and could not be described by the empirical function A?* with a constant value for a. A typical example is 9,lO-dicyanoanthracene whose values for k: exhibit a convex dependence on In r]. In accordance with this, the activation energy associated with k: was negative at low viscosities and displayed a transition from negative to positive values as the viscosity was increased. The values of the rate constant for the quenching by oxygen of the T1 states of the anthracene derivatives, k t , did not vary significantly, all being approximately 3 X lo9 M-1 s-l at 25 OC and 0.1 MPa. The logarithmic values of k;, when plotted as a function of In r], displayed appreciable downward curvature for all of the anthracene derivatives examined in this work.
“…When DMA is used as an emitting unit, both ground-state aggregates and excimers are formed in solid EC. In liquid EC, structured monomeric emission is observed (Figure a) and it has a mono-exponential decay whose decay time (10.3 ns) well matches the value reported for DMA in homogeneous solutions . After cooling the PCM below the T m , in addition to the structured emission spectrum (390–520 nm), the appearance of a broader band centered at 550 nm is observed (Figure a).…”
Section: Resultsmentioning
confidence: 80%
“…In liquid EC, structured monomeric emission is observed (Figure 2a) and it has a mono-exponential decay whose decay time (10.3 ns) well matches the value reported for DMA in homogeneous solutions. 28 After cooling the PCM below the T m , in addition to the structured emission spectrum (390−520 nm), the appearance of a broader band centered at 550 nm is observed (Figure 2a). The latter is due to excimer-like species, 29 as indicated by the good overlap of the excitation spectra collected at 427 and 540 nm (Figure 2b).…”
The prospect to tune the energy of emitting states through external stimuli opens the possibility to shift the energy of emitting units on demand and control the bimolecular processes they are involved in. To prove this concept, the fluorescence properties of three differently 9,10substituted anthracene derivatives are investigated in a phase change material (eicosane). The liquid-to-solid transition of the medium leads to an increase of the local dye concentration, a shortening of the intermolecular distances and the establishment of excited and ground-state interactions. As a result, a new contribution to the overall luminescence derives from the downshifted emission (up to 0.7 eV) from excimer-like species is observed. The addition of a second dye (a Pt-porphyrin) reduces the efficiency of excited and ground-state complexes between fluorophore units, although does not prevent the formation of multichromophoric aggregates where interactions between Pt-porphyrin and the emissive state of anthracene derivatives are observed.
“…Recently, we systematically investigated the quenching of the S 1 state of some aromatic molecules by the quenchers including oxygen as a function of pressure and found that k q is not described by eq 1 at high pressure as well as at 0.1 MPa. [7][8][9][10][11][12][13][14] For oxygen quenching of the fluorophore, 1 M*, we adopted a conventional scheme (Scheme 1) as the quenching mechanism where ( 1 M*O 2 ) en is an encounter complex between 1 M* and O 2 in the solvent cage, and k S is the unimolecular rate constant of deactivation of ( 1 M*O 2 ) en in the solvent cage.…”
Section: Introductionmentioning
confidence: 99%
“…High pressure is a powerful tool to investigate the nearly diffusion-controlled and/or diffusion-controlled reaction since it can change the solvent viscosity significantly and continuously without changing solvent and temperature. Recently, we systematically investigated the quenching of the S 1 state of some aromatic molecules by the quenchers including oxygen as a function of pressure and found that k q is not described by eq 1 at high pressure as well as at 0.1 MPa. − For oxygen quenching of the fluorophore, 1 M*, we adopted a conventional scheme (Scheme ) as the quenching mechanism where ( 1 M*O 2 ) en is an encounter complex between 1 M* and O 2 in the solvent cage, and k S is the unimolecular rate constant of deactivation of ( 1 M*O 2 ) en in the solvent cage. 1 …”
The fluorescence quenching by oxygen of 9,10-dimethylanthracene (DMEA) in liquid ethane and propane at pressures up to 60 MPa and 25 degrees C was investigated. The apparent activation volumes for the quenching rate constant, k(q),DeltaV++(q) , were 5.0 +/- 3.4 and 7.4 +/- 1.0 cm(3)/mol, whereas those for the solvent viscosity, eta,DeltaV++(eta) , were 190 +/- 22 and 42 +/- 1 cm(3)/mol in ethane and propane at 6.0 MPa, respectively. These results were discussed together with those in n-alkanes (C(4)-C(7)) and methylcyclohexane (MCH) that were previously reported, and it was found that DeltaV++(q) increases monotonically but DeltaV++(eta) decreases rapidly with increasing the number of carbon atoms in n-alkanes. The plot of ln k(q) against ln eta showed a leveling-off with decreasing eta. These observations were analyzed satisfactorily by the pressure dependence of the solvent viscosity on k(q) coupled with that of the radial distribution function, g(sigma), at contact with a hard sphere assumption. The apparent bimolecular rate constant, k(bim,0), for the quenching in the solvent cage was evaluated by extrapolating to g(sigma)eta = 0 in the plot of g(sigma)/k(q) against g(sigma)eta, and it was found that k(bim,0) decreased with increasing the radius of the solvent molecule. From the solvent size dependence of k(bim,0), the solvent cage effect was discussed phenomenologically.
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