Anthracene fluorescence efficiency

A wide variety of different classes of fluorescent molecules has been investigated in the peroxyoxalate chemiluminescent systems. Among those screened were fluorescent dyes such as rhodamines and fluoresceins, heterocyclic compounds such as benzoxazoles and benzothiazoles, and a number of polycyclic aromatic hydrocarbons such as anthracenes, tetracenes, and perylenes. The polycyclic aromatic hydrocarbons and some of their amino derivatives appear to be the best acceptors as they combine high fluorescence efficiency with high excitation efficiency in the chemiluminescent reaction [28],... 

Comparison of the Experimental and Simulation Results. The preceding discussion has shown that both the experimental anthracene fluorescence profiles and the simulated anthracene concentration profiles decrease in a manner which closely follows an exponential decay. Therefore, the most convenient way to compare the simulation results to the experimental data is to define an effective overall photosensitization rate constant, kx or k2, as described above. Adoption of this lumped-parameter effective kinetic constant allows us to conveniently and efficiently compare the experimental data to the simulation results by contrasting the rate constant obtained from the steady-state fluorescence decay with the value obtained from the simulated decrease in the anthracene concentration. 

Carbon disulfide quenches the fluorescence of anthracene quite efficiently,145,149 but seems to have little effect on its triplet lifetime.147 Diphenylanthracene in benzene fluoresces with a quantum yield of 0.8 and shows a high sensitivity to the oxygen concentration in photooxygenation reactions. With about 1 vol% of CS2 present, AC>2 is practically independent of [02] (> 10"5 mole/liter). In jjoth cases, where carbon disulfide was either used as solvent or was added to an otherwise strongly fluorescent solution, the quantum yields of photooxygenation followed... 

If one of the substances has a known fluorescence efficiency, the value of the other is then simply obtained. Convenient standard solutions are rhodamine B in ethanol with fluorescence in the yellow and efficiency 0.69, quinine bisulfate in 0.1 N sulfuric acid with fluorescence in the blue and efficiency 0.55. anthracene in ethanol with fluorescence in the violet and efficiency 0.27 in the ultraviolet region, naphthalene ( = 0.19), phenol (0 = 0.19), or benzene (0 = 0.042) can be used. With the last four compounds the solution must be deaerated by passing a current of nitrogen before measurement. To minimize the effect of errors in the spectral sensitivity curve it is desirable to use as the standard a solution... 

It has already been remarked that it is difficult to obtain reproducible values for the delayed fluorescence efficiency of phenanthrene from one solution to another. In ethanol, moderately high (though not reproducible) efficiencies have been observed but in highly purified n-hexane the efficiency was extremely low although anthracene gave similar results in both solvents. 

The longest wave absorption band of anthracene is short axis polarized. The substitution in 9,10 positions leads to a bathochromic shift in this band. The intrinsic lifetimes are proportional to Jandean be obtained from the area under the respective absorption curves. The molar extinction coefficients are 9, 10-dichloro-A > 9-chloro-A > A. The lifetime decreases with increase of absorbance and at the same time the fluorescence efficiency f is observed to increase. The values of f f°r various anthracenes in CC14 and the quantum efficiencies of their reactions with the solvent, both in absence of oxygen, are presented in Table 11.5. 

Stevens401 irradiated anthracene, 9-phenylanthracene, and 9,10-diphenylanthracene at 3600 A and 280-300°C. He found that both 02 and NO quenched the fluorescence with similar efficiencies. For anthracene at 280°C and 9-phenylanthracene at 300°C, the ratios of the quenching rate constant for NO to the fluorescence rate constant are, respectively, 1120 and 1380 M 1. Ware and Cunningham4384 found the rate constant to be 1.97 x 1011 M 1 sec-1 for the quenching of anthracene vapor by NO at 280°C. They also found the anthracene-fluorescence constant to be 3.51 x 107 sec-1. The ratio of their two rate constants is 5500 M-1, about a factor of five larger than that found by Stevens. 

Birks and Black showed experimentally that the fluorescence efficiency of anthracene bombarded by alphas varies with total dose as... 

The apparent bimolecular rate parameters > STS characteristic of the external heavy-atom quenching of the molecular singlet and triplet states of anthracene (A) (solvent = cyclohexane, quenchers = bromobenzene and ethyl iodide) and 9,10-dibromoanthracene (DBA) (solvent = ethanol, quencher = KI) have been determined and used to describe the sensitivity of the external heavy-atom effect acting on the non-radiative Sx - Tx and T -> S0 processes.141 142 The interesting observation that ethyl iodide and benzene increase the fluorescence efficiency from excited dibromoanthracene has been explained in terms of the formation of photoassociation product E (exciplex ).141b This species then undergoes its own characteristic photophysics. The dominant processes for the ethyl iodide case are ... 

Substances which display fluorescence are generally delocalized aromatic systems with or without polar substituents (Fig. 1). It is difficult to predict which molecules will be fluorescent or non-fluorescent because exceptions can usueilly be found. However, several general rules are generally true. Rigid molecules are usually more fluorescent, or at least their fluorescence more predictable, than molecules with the possibility of internal rotation. Hence, perylene and anthracene fluoresce with high efficiencies, whereas stilbene can be much less efficient. In viscous solvents, in which rotational reorientation to c/s-stUbene cannot occur, tran -stilbene is highly fluorescent. In non-viscous solution stilbene is only weakly fluorescent. This illustrates an important aspect of fluorescence, which is that the excited states are involved. 

Fig. 6.6. Stern-Volmer plot of quantum efficiency in quenching of anthracene fluorescence by N-N diethylaniline in toluene solvent [H. Knibbe, Ph. D. Thesis (Free University of Amsterdam 1969), p. 44].

The method adopted by Liithi and Waser [177] is to mix the thin layer material (usually silica gel) with the scintillator in a suitable ratio and then run the compounds to be separated on this mixture. This technique has been used to separate tertiary and quaternary amines such as hexamethonium and trimethylamine [177]. Anthracene was used because it is only slightly soluble in most solvents used in chromatography and it possesses a high fluorescent efficiency. This is enhanced further by lowering the temperature and in practice the fluorograms are exposed at — 70°C. 

Nevertheless the fluorescence efficiency of the substituted phthalate dianion is a decisive factor in luminol type chemiluminescence. Since one can expect that the carboxylates of higher condensed aromatic hydrocarbons would exhibit high fluorescence efficiencies, a series of naphthalene-, anthracene- and homologuous o-dicarboxylic acid hydrazides have been synthesized and their chemiluminescence investigated. In the tables in Appendix, p. 205 some of these hydrazides synthesized since 1968 are listed. 

In (25) there is a true fluorescer moiety in the cyclophane system, and it represents a donor-acceptor complex system, whereas (24) and (23) very probably are forming exciplexes on oxidation [41]. The higher efficiency of this paracyclophane energy transfer in comparison with the methylene-linked energizer and fluorescer as in (22) is seen from the fact that in (22) the DPA-residue, having a fluorescence quantum yield of nearly unity exhibits a chemiluminescence efficiency of 26% of that of luminol whereas in (25) with the 1,4-dimethyl anthracene fluorescer (0jn ca. 0.30) a light yield of 100% luminol [41] is obtained. 

Midinger and Wilkinson<54> have used flash photolysis and fluorescence quenching by heavy atoms to determine the intersystem crossing efficiencies of anthracene and a number of its derivatives. As discussed in Section 5.2b, heavy atoms present as molecular substituents or in the solvent serve to promote multiplicity forbidden transitions. When anthracene is excited the following processes can occur ... 

They observed a constant quantum yield of fluorescence (Or = 0.3) for all members of the series independent of whether the anthracene moiety absorbed and emitted the energy or the naphthalene moiety absorbed the energy and transferred it to the anthracene moiety. Thus at these short distances singlet energy transfer is 100% efficient. 

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>. 

Blue fluorescent emitters based on fused polyaromatic ring systems have long been known and systematic work has steadily improved the efficiencies and colors, while pushing the limits of stability in an operational device. A sky blue based on styrylamine doped 2-methyl-9,10-di(2-naphthyl)anthracene OLED was reported to provide the highest efficiency device (Scheme 3.99) [365],... 

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