Quencher anthracene

Chemically inert triplet quenchers e.g. trans-stilbene, anthracene, or pyrene, suppress the characteristic chemiluminescence of radical-ion recombination. When these quenchers are capable of fluorescence, as are anthracene and pyrene, the energy of the radical-ion recombination reaction is used for the excitation of the quencher fluorescence 15°). Trans-stilbene is a chemically inert 162> triplet quencher which is especially efficient where the energy of the first excited triplet state of a primary product is about 0.2 eV above that of trans-stilbene 163>. This condition is realized, for example, in the energy-deficient chemiluminescent system 10-methyl-phenothiazian radical cation and fluoranthene radical anion 164>. 

Polynuclear aromatic hydrocarbons can be oxidized photolytically with the formation of cyclic peroxide. For example, anthracene is photooxidized to peroxide with the quantum yield 0 = 1.0 [205], The introduction of quenchers lowers the peroxide yield. 

The photochemical reaction can also proceed via the triplet state and in this case no cyclization is observed. Especially when acetophenone is added as a triplet sensitizer, 41 is not formed. Remarkable is the observation that in the presence of anthracene or pyrene as triplet quencher, the yield of the cyclization product 41 was not enhanced and that nitrene insertion into CH bonds of anthracene or pyrene was observed. When the photochemical cyclization reaction was performed with the tosyl azide derivative 42a or the azido nitrile derivative 42b (Scheme 6), only low yields of the tricyclic amide 41 (32% from 42a, 9% from 42b, respectively) were obtained <2001JCS(PI)2476>. 

Reactions (30) and (31) may give the same products. In (31) the polarization energy decreases the energy demand for temporal charge separation and it can be exothermic when B has a considerable electron affinity. For aromatic hydrocarbon quenchers (e.g., anthracene) such mechanism leads to dissipation of the excitation energy on the vibrational levels. When the quencher molecules contain Cl or Br atom in the intermediate step, Cl or Br elimination is expected, e.g., with benzyl chloride additive ... 

At very short times, very little motion of reactants has occurred so that little, if any, reaction will have taken place. But the manner of creation of the mixture of A and B reactants should be considered. A very simple means of preparing a reaction mixture is by photolysis. For instance, consider a solution of anthracene and carbon tetrabromide. Photostimulation of anthracene with an extremely short duration light pulse produces excited singlet (and triplet) states. The carbon tetrabromide quenches the excited singlet state fluorescence very efficiently. Just before the photostimulation event, the quencher (i.e. B) is randomly distributed throughout the system volume and for a short time after photostimulation, it remains randomly distributed. With the exception of the location where the fluorophor A is, there is no preferred location of the quencher B. No... 

While no spectroscopic evidence of a ground-state complex between anthracene and carbon tetrachloride, naphthalene or 1,2-benzanthracene and carbon tetrabromide has been found, Nemzek and Ware [7] were unable to explain their steady-state fluorescence quenching measurements with the parameters deduced from the determination of the time-dependent rate coefficients unless a ground-state complex was present. This cannot be regarded as a satisfactory and consistent analysis because the time-dependent rate coefficient would be modified by the presence of the initial distribution of quencher and fluorophor in the ground state. 

Anthracene and substituted anthracenes are also known to sensitize the dimerization of 1,3-cyclohexadiene, another triplet state process [E(7,) for 1,3-cyclohexadiene = 53 kcal/mol] [28]. In similar experiments, the 72 state of naphthalene was also shown to undergo energy transfer to quenchers [29]. 

Since these first time-resolved studies, similar quenching methods (i.e., choosing an exclusive upper state quencher) have been used in conjunction with the two-color approach to demonstrate energy transfer from anthracene T2 to acrylonitrile, benzonitrile, dimethoxybenzene [52] and from the upper triplets of 70, 71 and p-terphenyl to a variety of quenchers including carbon tetrachloride [53]. 

Another recent study makes use of the participation of the T2 state in the S - TISC process in anthracene [31]. 1,3-Octadiene was used to intercept some of the T2 states before they relaxed to Tx and the decrease in 7, yield was used to estimate the T2 lifetime. Further, this study compensated for the effects of static and time-dependent quenching that comes into play at the relatively large quencher concentrations that are required when quenching sub-nanosecond-lifetime transients. The lifetimes obtained (given in Table 5) were significantly less than previously estimated from other quenching studies and are in line with the lifetimes implied from the T-T fluorescence quantum yields discussed above. 

Enhancement in the performance of OLEDs can be achieved by balanced charge injection and charge transport. The charge transport is related to the drift mobility of charge carriers. Liu et al. [166] reported blue emission from OLED based on mixed host structure. A mixed host structure consists of two different hosts NPB and 9,10-bis(2 -naphthyl)anthracene (BNA) and one dopant 4,4 -bis(2,2-diphenylvinyl)-l,l -biphenyl (ethylhexyloxy)-l,4-phenylene vinylene (DPVBi) material. They reported significant improvement in device lifetime compared to single host OLEDs. The improvement in the lifetime was attributed to the elimination of heterojunction interface and prevention to formation of fluorescence quenchers. Luminance of 80,370 cd/m2 at 10 V and luminous efficiency of 1.8 cd/A were reported. 

Change in solvent polarity has been shown to alfect the relative contribution of exciton resonance and charge transfer to the stabilisation of excited complexes (Eunice et al., 1979). It was found, for example, that the quenching of the fluorescence of anthracene by amines and phosphines in nonpolar solvents showed a better correlation between log and the singlet energy of the quencher than with the oxidation potential of the quencher. The reverse is true when polar solvents are used, showing, as had been postulated in earlier work (Davidson and Lambeth, 1969), that charge transfer is important in such solvents. 

Chromophore quencher systems where the organic molecular components are aryl hydrocarbons are under intense study [67, 190-205], In these systems an inorganic moiety (based on polypyridine complexes of Ru(II), Os(II), Re(I)) and an aryl hydrocarbon (naphthalene, anthracene, pyrene) are covalently linked by flexible aliphatic [187-201] or rigid conjugated bridges [49, 190, 191, 193). 

In dyads formed by the Ru(bpy)3 + complex and an anthracene moiety (25), a strong quenching of the MLCT luminescence of the Ru-based unit is observed [195], This quenching is attributed to exergonic triplet-triplet energy transfer from the metal complex to anthracene. The process, in which anthracene acts as an EnT quencher, is represented in Figure 18. A similar behavior has been observed in a dyad formed by a Re(bpy)(CO)3 unit and an anthracene moiety [202]. 

Limited numbers of studies have been reported on the properties of molecules in the T states. Two-color two-laser flash photolysis can be applied to study photoinduced reactions from the T states. It has been reported that the main reaction path from the T states is the triplet ENT to the triplet quenchers. To the best of our knowledge, there has been only one report on the ELT from the T state. Wang et al. [48] reported the ELT from anthracene(T2) to ethyl bromoacetate. However, no detailed mechanism of the ELT from the T state has been reported. In this section, we summarize our recent systematic study of the intermolecular ELT from a series of substituted naphthalenes (NpD) in the T state to electron acceptors [85, 86]. 

The enol silyl ether (56) undergoes a photoinduced reaction in the presence of chloranil to give cyclohexenone and the adduct (57) and the currently available evidence suggests that the reaction proceeds by electron transfer to the photo-activated chloranil to give (56) A photophysical study has appeared of the chromophore-quencher compounds [Au(CCPh)(L )] (L = 10-[(diphenylphosphi-no)methyl]anthracene) and [Au(CCPh)(L )]BPh4 (L = l-[2-(diphenylphosphin-oxy)ethyl]pyridinium], 1 -[2-(diphenylphosphinoxy)ethyl]-4-methyl pyridinium, 1 -[2-(diphenylphosphinoxy)ethyl]-4-tert-butylpyridinium, and 1 -[2-(diphenylpho-sphinoxy)ethyl]triethylammonium in which the Au(CCPh) chromophore is linked by a flexible tether to the acceptors. 

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