Emission quantum yields, chemiluminescence

DPA) in dimethylphthalate at about 70°, yields a relatively strong blue Umax =435 nm) chemiluminescence the quantum yield is about 7% that of luminol 64>. The emission spectrum matches that of DPA fluorescence so that the available excitation energy is more than 70 kcal/mole. Energy transfer was observed on other fluorescers, e.g. rubrene and fluorescein. The mechansim of the phthaloyl peroxide/fluorescer chemiluminescence reaction very probably involves radicals. Luminol also chemiluminesces when heated with phthaloyl peroxide but only in the presence of base, which suggests another mechanism. The products of phthaloyl peroxide thermolysis are carbon dioxide, benzoic acid, phthalic anhydride, o-phenyl benzoic acid and some other compounds 65>66>. It is not yet known which of them is the key intermediate which transfers its excitation energy to the fluorescer. 

Emergency Response Guidebook, 747 Emission quantum yields, chemiluminescence, 1221, 1222-3... 

This is the process studied experimentally in Refs. 191 and 192 through the luminescence coming from the triplet excited state D. The quantum yield of excitations 4>es can be extracted from the electro-chemiluminescence quantum yield 4>ecl if the emission quantum yield from the excited state < )e is known [191] ... 

The autoxidation of other phosphonate carbanions derived from diethyl diphenylmethylphosphonate (9) and diethyl fluorenylphosphonate (10) showed that DBA (9,10-dibromoanthracene, a triplet energy aacceptor) enhanced the chemiluminescence in spite of the lower energy for the excited triplet benzophenone (68-69 kcal/mol) and fluorenone (53 kcal/mol) than that for singlet DBA (71 kcal/mol). The Stem-Volmer plot of the double reciprocal of the DBA concentration and the chemiluminescence quantum yields established a bimolecular process with the fluorophor and the excited species in these chemiluminescence reactions. The emission quantum yields at the infinitive DBA concentration were calculated to be... 

It can be seen from the above that it is necessary to account for coUisional effects on the emission quantum yields when interpreting chemiluminescence profiles to deduce mechanistic information. In this section, we summarize the results of a series of experiments on quenching and energy transfer in electronically excited OH and CH, which are pertinent to such flame studies. 

The overall reaction scheme of the luminol chemiluminescence in an aqueous medium is shown in Figure 1. The luminol oxidation leads to the formation of an aminophthalate ion in an excited state, which then emits light on return to the ground state. The quantum yield of the reaction is low ( 0.01) compared with bioluminescence reactions and the emission spectrum shows a maximum1 at 425 nm. 

Very weak chemiluminescence (quantum yields of 6.5.. . 9.1 X 10-10) in the spectral ranges 400. 540 nm (benzaldehyde phosphorescence) and 600 nm (emission from excited singlet oxygen collision pairs)) was also observed on thermolysis of 5 with no fluorescer present. 

This is not due to the relatively extended aromatic system in 25, for C. C. Wei and E. H. White 96> recently succeeded in synthesizing the benzoperylene compound 27 which is the most efficient hydrazide yet known with a chemiluminescence quantum yield of 7.3 % (in DMSO/ t-BuOK/02). The corresponding dicarboxylate has a fluorescence efficiency of 14% and emits at 420 and 450 nm which matches the chemiluminescence emission of 27 9 ). 

A spectro-radiometer-luminometer for chemiluminescence and fluorescence quantum yield studies has been described by B. G. Roberts and H. C. Hirt 187>. To obtain emission spectra from very weak chemiluminescence reactions, a large-aperture spectrograph combined with a sensitive image-intensifier tube has been used68 this was developed from a device previously constructed by Bass and Kessler 188>. With it, it was possible to record the very weak emission of singlet oxygen dimer... 

Luminol amidine 132, synthesized from luminol and the Vilsmeier reagent from DMF and thionyl chloride, has been proposed as a suitable luminol derivative for analytical purposes because, unlike luminol, it can be easily purified by recrystallization from water. 132 exhibits a chemiluminescence quantum yield of about 20% of luminol in ferricyanide-catalyzed oxidation by aqueous alkaline hydrogen peroxide Amax of the emission is 452 nm 196>. 

Lee and coworkers postulated the involvement of 50 and 51 (Ar = 2,4-dinitrophenyl) as two HEIs formed in parallel in the uncatalyzed reaction of DNPO and hydrogen peroxide in the presence of perylene. Due to the experimental observations of light emission from the reaction of DNPO and TCPO also in the absence of hydrogen peroxide, Lee and coworkers postulated the involvement of a nonperoxidic HEI (additionally to 51 and 3, 48 or 52) under these conditions. However, neither chemiluminescence quantum yields nor even relative emission intensities have been reported. Furthermore, it was shown " that the intensities and the chemiluminescence quantum yields in the absence of hydrogen peroxide are five orders of magnitude lower than in the presence of 10 M H2O2, indicating that the proposed additional pathway is of extremely low efficiency for excited-state... 

Another method of measuring the relative quantum yield of the radical decomposition process (eq. 22) was also devised recently (144). This involves HNO chemiluminescence photoexcitation spectroscopy. When an H atom recombines with an NO molecule, an electronically excited HN0 ( A A" ) is formed. Fluorescence emission from HNO occurs at 762 nm. The HNO chemiluminescence in a low-pressure 1 10 mixture of H2CO and NO is proportional to the H-atom quantum yield from the photolysis of H2CO. The photoexcited HNO (red) chemiluminescence excitation spectrum of a H2CO/NO mixture obtained with a tunable laser at high resolution is shown in Fig. 2 together with an absorption spectrum and a H2CO fluorescence (blue) excitation spectrum (237). The relevant reaction scheme is as follows ... 

Chemiluminescence quantum yields were studied as a function of the driving force for series of reactions between [Ru(N,N)3] + and [Co(N,N)3]+. The yield of [Ru(N,N)3] + emission decreases from 0.31 to 0.07 with decreasing driving force [339]. 

For the experimental determination of the 0, it is necessary to quantify the light output of the direct chemiluminescent process. The experimental definition of the direct chemiluminescence quantum yield is given in Eq. 36, that is, the initial rate of photon production (/q ) per initial rate of dioxetane decomposition k )[D]o). Alternatively, the total or integrated light intensity per total dioxetane decomposed can be used. The /t )[Z)]o term is readily assessed by following the kinetics of the chemiluminescence decay, which is usually first order. Thus, from a semilogarithmic plot of the emission intensity vs. time, the dioxetane decomposition rate constant kjj is obtained and the initial dioxetane concentration [Z)]o is known,especially if the dioxetanes have been isolated and purified. In those cases in which the dioxetanes are too labile for isolation and purification, [/)]o is determined by quantitative spectroscopic measurements or iodometric titration. 

The energy-transfer term 0 x is unity under conditions of infinite DPA concentration. What is typically done is that one measures the DPA-enhanced chemiluminescence intensity (/dpa) function of DPA concentrations and constructs a plot of 1//dpa vs. 1/[DPA]. The intercept of such a double reciprocal plot represents the DPA-enhanced chemiluminescence intensity at infinite DPA concentration, that is, /foPA] - The DPA-enhanced chemiluminescence quantum yield that is calculated from this emission intensity, that is, 0fDPA] > represents complete singlet-singlet energy transfer, that is, 0 x is unity. 

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