Chemiluminescence quantum yield

In principle, one molecule of a chemiluminescent reactant can react to form one electronically excited molecule, which in turn can emit one photon of light. Thus one mole of reactant can generate Avogadro s number of photons defined as one einstein (ein). Light yields can therefore be defined in the same terms as chemical product yields, in units of einsteins of light emitted per mole of chemiluminescent reactant. This is the chemiluminescence quantum yield which can be as high as 1 ein/mol or 100%. 

A substantial effort has been appHed to iacreaskig i by stmctural modification (114), eg, the phthalaziQe-l,4-diones (33) and (34) which have chemiluminescence quantum yields substantially higher than luminol (115,116). The fluorescence quantum yield of the dicarboxylate product from (34) is 14%, and the yield of singlet excited state is calculated to be 50% (116). Substitution of the 3-amino group of lumiaol reduces the CL efficiency > 10 — fold, whereas the opposite effect occurs with the 4-amino isomer (117). A series of pyridopyridaziae derivatives (35) have been synthesized and shown to be more efficient than luminol (118). 

C is the concentration of limiting reactant in mol/L, c is the chemiluminescence quantum yield in ein/mol, and P is a photopic factor that is determined by the sensitivity of the human eye to the spectral distribution of the light. Because the human eye is most responsive to yellow light, where the photopic factor for a yellow fluorescer such as fluorescein can be as high as 0.85, blue or red formulations have inherently lower light capacities. 

Therefore a low chemiluminescence quantum yield can be due to the fact that the fluorescence efficiency of the product molecules is high but the chemical efficiency of the reaction producing excited molecules is low, or the reverse, or that ifies and n are both low. 

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. 

Hydrazide chemiluminescence has been investigated very intensively during recent years (for reviews, see 1>, p. 63, 2>, 90>). Main topics in this field are synthesis of highly chemiluminescent cyclic diacyl hydrazides derived from aromatic hydrocarbons, relations between chemiluminescence quantum yield and fluorescence efficiency of the dicarboxylates produced in the reaction, studies concerning the mechanism of luminol type chemiluminescence, and energy-transfer problems. 

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 ). 

As can be seen from Table 2, certain phenanthrene derivatives produce more chemiluminescence than luminol. The diphenyl derivative 33 diluminyl evidently has its benzene rings in a non-coplanar position this is apparent from the fact that this compound does not behave as a benzidine derivative under the oxidative conditions of chemiluminescence reactions. The chemiluminescence quantum yield is only about one third that of luminol 100>. 

Table 5. Luminol chemiluminescence quantum yields in different solvents with some oxidative systems (after J. Lee and H. H. Seliger 115>)...

Luminol concentration (M) Solvent T[°C] pB Reaction conditions Chemiluminescence quantum yields Qo... 

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>. 

Scheme 28) Quantum yields of lucigenin oxidation by hydrogen peroxide in alkaline media are comparable with the values obtained in luminol oxidation (1.24 x 10 E mol ) ° . However, the use of other peroxides, such as tcrt-butyl hydroperoxide, results in a decrease of chemiluminescence quantum yields of two orders of magnitude, confuming the hypothesis that a 1,2-dioxetane is the HEI, since its formation would be impossible with alkyl peroxides . 

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... 

Rauhut and coworkers proposed the occurrence of a charge transfer complex between the HEI and the ACT in order to explain the electronically excited-state generation in the peroxyoxalate system. Chemiluminescence quantum yield (4>cl) measurements with different activators have shown that the lower the ACT half-wave oxidation potential (Ei/2° ) or singlet energy (Es), the higher the electronically excited-state formation rate and 4>cl- According to the mechanistic proposal of Schuster and coworkers for the CIEEL... 

Dimethyl-1,2-dioxetanone, chemiluminescence quantum yield, 1226-7 Dimethyldioxirane epoxidation atkenes, 37-44 deuteriation, 1143 O NMR spectroscopy, 184-5 preparation, 26, 1130-2 structure, 26... 

Diphenylmethane, chemiluminescence quantum yields, 1235, 1238, 1268 Diphenyl-1 -naphthylphosphine, peroxide value, 659... 

TABLE 3. Luminol chemiluminescence quantum yields in different solvents with some oxidative... 

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] ... 

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]. 

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