The chemiluminescence of organic compounds

Abstract

The chemiluminescence of organic compounds in solution is briefly surveyed with some emphasis on the mechanisms which result in relatively efficient population of an excited state of a product molecule. This is done in terms of the relation l/J = l/Jc x l/JE x l/JF with particular reference to peroxide compositions. INTRODUCTIONThe study of chemiluminescence mechanism in a persistent and systematic fashion is an activity largely confined to the last decade. This is not surprising when one considers that the problems associated with ground-excited state interactions must be multiplied by the complexities of a vigoraus oxidative reaction for a full description of a chemiluminescent reaction. A general survey of the phenomenon discloses that, with almost no exceptions, oxidation is involved, the mechanism ranging from the relative simplicity of an electron transfer reaction to the confusion of a many step, bond cleavage process. The excitation step in certain bioluminescent reactions is of particular interest as an example of the latter kind. Although luminescence in the gas phase has been comparatively weil understood for a long time, there are various reasons why the problern of chemiluminescence in solution must be approached differently. All gas phase reactions emitting light involve di-or tri-atomic molecules and often atom recombination. The restriction of the degrees of freedom in small molecules and the near absence of collision in the gas phase Ieads to a non-equilibrium distribution of the energy derived from the exotherrnie reaction. If one assumes that the reactants in an exotherrnie reaction in solution are, within the lifetime of an excited species, in equilibrium with the surrounding solvent, then it is obvious that in this case vibrational energy, no matter how great, is an unlikely source of electronic excitation. Thus of the various mechanisms for organic chemiluminescence, electron transfer is particularly attractive. Conversely, there is no weil proven instance ofthe emission oflight from a radical recombination reaction in solution, although the bonds formed in such a process usually release more than sufficient energy to populate an electronically excited state. A further consequence of the conditions under which most organic chemiIuminescent reactions occur is the observation that emission is from the first excited singlet state, the triplet state being easily quenched. However, there

Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane

“…31 Simultaneously, the obtained dark mechanism indicates that reactions in which dioxetanes are formed as intermediates do not necessarily have to produce light. Hence, dissociation channel of Dewar dioxetane on the triplet excited state manifold gives rise to a radiationless decay, whereas decomposition on the singlet excited state manifold, which require higher energies, produces an excited species that may decay by fluorescence.…”

“…31 Table S6). A second energy barrier, related to the C 2 -C' 2 bond breaking, is needed to dissociate the molecule in the excited state surface, with a slightly lower activation energy on the triplet manifold.…”

“…12,31 McCapra referred to it in the study of the isomerization of Dewar benzene into benzene in the excited state (see Figure 3a). 31 According to the Woodward-Hoffmann rule, this transformation is symmetry-forbidden.…”

“…12,31 McCapra referred to it in the study of the isomerization of Dewar benzene into benzene in the excited state (see Figure 3a). 31 According to the Woodward-Hoffmann rule, this transformation is symmetry-forbidden. 32 Indeed, the activation energy of 90 kcal/mol reported by McCapra prevents the benzene product to be achieved thermally (see Figure 3a).…”

Chemiluminescence Immunoassay for Progesterone in Plasma Incorporating Acridinium Ester Labelled Antigen

“…This reaction is less susceptible to background interference and more sensitive than that for isoluminoI. 12 This fact, together with their higher quantum light yield (2-5%) and well documented reaction mechanisms 13 has led to the use of acridinium derived labels in an increasing number of immunoassays.P:"…”