Study of the Fractional Power Dependence on Solvent Viscosity of the Rate Constant for Bimolecular Diffusion-Influenced Quenching Reactions between Oxygen and the Singlet and Triplet States of Anthracene Derivatives

Abstract

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.

Inverse correlation between efficiency of singlet oxygen production and rate constant for oxygen quenching in the S1 state of anthracene derivatives

“…1,2 It was demonstrated for many molecules that k S q was approximately a diffusion-controlled value whereas the rate constant (k T q ) for oxygen quenching of the lowest excited triplet state (T 1 ) was roughly 1/9 of k S q , and this observation was explained reasonably in terms of the difference of spin-multiplicity in the energy transfer from the two excited states to oxygen. As shown in previous papers, [3][4][5][6][7] k S q of anthracenes substituted at the meso-position depends significantly on the electron-donating character of the substituent and is fairly smaller than a diffusion-controlled limit for the derivatives possessing electron-withdrawing substituents such as 9,10dicyanoanthracene (DCNA), CNA and DCLA.…”

“…In previous papers, the effect of substituent on k S q was explained as the difference between the electron-donating group and the electron-withdrawing group. 3,4 Including DCNA whose f S D and k S q are reported as unity in cyclohexane 15 and 3.2 Â 10 9 M À1 s À1 in methylcyclohexane, 3,4 respectively, it is deduced that large f S D -values for CNA, DCLA and DCNA are related to small k S q -values of these compounds.…”

“…29 The average fluorescence energy (E av F ¼ hn av F ) was calculated from the corrected fluorescence spectrum by eqn. (4).…”

Human plasma dynamically quenches the fluorescein at the initial point of oxygen radical absorption capacity (ORAC) assay

“…Therefore, we can infer that the quenching is not partly or fully imparted by plasma proteins. Other potential fluorescence quenchers present in human plasma are found to be molecular oxygen [9–14] and uric acid derivatives like porphyrin uric acid [15]. However, we could not recognize the molecule due to lack of facilities.…”

Contribution of local density augmentation in the vicinity of 9-cyanoanthracene and dynamic fluorescence quenching by oxygen in liquid and supercritical carbon dioxide

“…In general, the fluorescence quenching by oxygen of some aromatic molecules is very efficient and has often been believed to be diffusion-controlled in liquid solution. [19][20][21][22][23] In fact, for meso-substituted anthracene derivatives with electron donating substituents, such as 9,10-dimethylanthracene (DMEA), the quenching is nearly diffusion-controlled. 24 However, for meso-substituted anthracence derivatives with electron withdrawing substituents, such as 9,10-dicyanoanthracene (DCNA), the rate constant for quenching, k q , is smaller by about one order of magnitude than that for diffusion (k q $ 10 9 M À1 s À1 ).…”