Naphthalene fluorescence quantum yield

Dinaphthotetraazaporphyrins are structural isomers of phthalocyanines. The zinc complex was formed and the properties compared to zinc phthalocyanines demonstrating a lower fluorescence quantum yield for the zinc-fused naphthalene porphyrin (D2h symmetry) vs. the zinc phthalocyanine (D4h)S36... 

The amine-reactive 5-(dimethylamino)naphthalene-l-sulfonyl (dansyl) chloride 28 [80] and related fluorophores [81, 82], as well as the 5-((2 aminoethyl)amino) naphthalene-1-sulfonic acid (EDANS) 29, are included in the naphthalene fluorophore family. Derivatives of the latter, such as compound 30, exhibit a Lm.ix/ Lem 336/520 nm, molar absorptivity (e) of 6.1 x 103 M-1 cm-1, and a fluorescent quantum yield of 0.27 in water [83], The use of EDANS is particularly interesting in FRET experiments [84, 85]. Furthermore, 4-amino-3,6-disulfonylnaphthalimides (e.g., Lucifer yellow 31), associated to a longer absorption (Lmax 428 nm) [86] are suitable polar tracers [87]. 

Substituent groups have a marked effect on the fluorescence quantum yield of many compounds. Electron-donating groups such as -OH, -NH2 and -NR.2 enhance the fluorescence efficiency, whereas electron-withdrawing groups such as -CHO, -C02H and -N02 reduce the fluorescence quantum yield, as shown by naphthalene and its derivatives in Table 4.3. 

Table 4.3 The effect of substituent groups on fluorescence efficiency of naphthalene and its derivatives. Fluorescence quantum yields measured in fluid solution at room temperature...

Fukuda et al. (1988) studied the photolysis of naphthalene in distilled water using a high pressure mercury lamp. After 96 h of irradiation, a rate constant of 0.028/h with a half-life of 25 h was determined. When the experiment was replicated in the presence of various NaCl concentrations, they found that the rate of photolysis increased proportionately to the concentration of NaCl. The photolysis rates of naphthalene at NaCl concentrations of 0.2, 0.3, 0.4, and 0.5 M following 3 h of irradiation were 33.3, 50.6, 91.6, and 99.2%, respectively. It appeared that the presence of NaCl, the main component in seawater, is the cause for the increased rate of degradation. Schwarz and Wasik (1976) reported a fluorescence quantum yield of 0.16 for naphthalene in water. 

Substituents have considerable influence on emission characteristics of aromatic compounds. Heavy atom substituents tend to reduce the fluorescence quantum yield 4>f in favour of phosphorescence emission f. In halogen series the effect increases in the order F < Cl < Br < I. In Table 5.1 are recorded experimental data for halogen substituted Naphthalenes. 

Two-substituted naphthalene thienyl oligomers have been characterized for their photophysical properties (09PCCP8706). The compound 7 showed absorption at 405 nm and an emission at 475 and 502 nm. The fluorescence quantum yield was 0.27 and tf 0.56 ns. The quantum yield for the internal conversion was 0.05, while the triplet quantum yield resulted to be 0.68. 

A similar effect of the CDs on the fluorescence of 2-(p-toluidinyl)naph-thalene-6-sulfonate (2) was reported by Kondo and co-workers [55], who demonstrated the existence of complexes with different stoichiometry by applying the Benesi-Hildebrand treatment to the fluorescence variations of 2 as a function of CD concentration. For a-CD, the Benesi-Hildebrand plot—reciprocal fluorescence intensity versus reciprocal CD concentration—was a straight line, whereas for / - and y-CD it deviated from the linearity at high CD concentrations. This indicates that a 1 1 complex is formed between a-CD and 2, while / - and y- CD also form 2 1 (host guest) complexes. It was suggested that CD complexes 2 by including the toluidinyl moiety of the probe. In complexes with 2 1 stoichiometry, the CDs include the naphthalene moiety as well as the toluidinyl part of 2. This mode of complexation for 2 with a- and /S-CD was confirmed in reference 56. The fluorescence quantum yields for 1 1 and 2 1 complexes are reported in Table 1. 

This process is evidenced by the anthracene fluorescence, which is quite distinct from that of naphthalene. The quantum yield of anthracene sensitization... 

NIR fluorophores are generally considered as substances that emit fluorescence in the NIR region (650-900 nm). Particularly, the fluorescence quantum yield (QY) of NIR fluorophores is always lower than that of short wavelength emission ones. Over the past few decades, enormous progress has been made in the field of NIR fluorescent dyes. There are several major NIR organic fluorescent chromophores, such as bay-substituted perylene or naphthalene bisimides, cyanine dyes, BODIPYs, DPPs, and porphyrins. 

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. 

A singlet naphthalene or a singlet exciplex is thought to be the reactive species in this reaction since the quantum yield of cycloaddition parallels the quenching of naphthalene fluorescence by acrylonitrile. 

Finally, the hydrazide 29 98> is strongly fluorescent in neutral solution (e.g. in dioxane), the fluorescence intensity amounting to about 200% of that of 7-dimethylamino-naphthalene-1.2 dicarboxylic hydrazide 30, which is one of the best chemiluminescent hydrazides 97b The 5-isomer, however, is very poor in chemiluminescence in an aqueous system (hemin-catalyzed oxidation with aqueous alkaline hydrogen peroxide), the light yield being only 1 % of that of the 7-isomer in DMSO/t-Bu0K/02 its quantum yield is slightly better but very distinctly below that of 30 98>">. It should be mentioned that in aqueous alkaline solu-... 

The confusion generated in the initial report185 on photoracemization of sulfoxides has recently been removed with the postulate that naphthalene singlet forms an excited complex with sulfoxides.186 Thus, despite the fact that the singlet state of 36 lies at 113 kcal, some 23 kcal above that of naphthalene, 36 quenches the fluorescence of this hydrocarbon with kes = 3.2 x 107Af -1 sec-1. From the dependence of the quantum yield of racemization on sulfoxide concentration (Eq. 34), a value of kes = 2.3 x 107Af-1 sec-1 was deduced. Since these values are the same within experimental error, it follows that the singlet state of naphthalene is responsible for photoracemization. 

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