Excited states, acid-base properties

Reinvestigation of the excited state acid-base properties of 2-naphthylamine (Schulman and Capomacchia, 1972) showed that a reported change of hybridization from sp3 to sp2 on excitation had little effect on the entropy of protonation of nitrogen in the Sx state and that therefore the Forster cycle was still applicable. A pX (S1 )-value, calculated from the fluorescence maxima of the B and BH+ form, of —8-1 is in poor agreement with the value, —2, obtained from fluorescence titration measurements. From the acidity dependence of fluorescence intensity for 1- and 2-naphthylamine Liedke and Schulman (1973a) found that the decrease in emission of the B form occurred at lower acidities than the appearance of BH+ fluorescence. [A similar titration curve for the fluorescence of the neutral molecule was obtained by Seliskar and Brand (1971), who obtained a value of 0-64 for pkr(S1) from the decrease of the... 

Ireland J F and Wyatt PAH 1976 Acid-base properties of electronically excited states of organic molecules Adi/. Rhys. Org. Chem. 12 131-221... 

Acid-base properties of electronically excited states of organic molecules, 12, 131... 

Electronically excited states of organic molecules, acid-base properties of, 12,131 Energetic tritium and carbon atoms, reactions of, with organic compounds, 2, 201 Enolisation of simple carbonyl compounds and related reactions, 18,1 Entropies of activation and mechanisms of reactions in solution, 1,1 Enzymatic catalysis, physical organic model systems and the problem of, 11, 1 Enzyme action, catalysis of micelles, membranes and other aqueous aggregates as models of, 17. 435... 

Electronically excited states of organic molecules, acid-base properties of, 12, 131 Energetic tritium and carbon atoms, reactions of, with organic compounds, 2, 201... 

E. Van Der Donckt, Acid-base-properties of excited states, Prog. React. Kinet. 5, 273-299 (1970). 

The acid-base properties of the ground and excited states of [Ru(bpy)2(im)2] and [Ru(bpy)2(l,2,4-triazole)2] have been investigated. Both complexes are stronger acids in the excited than the ground states." Representative triazoles, L or HL, have been incorporated into the complexes [Ru(bpy)2L]"" (n = 1 or 2). Electronic spectroscopic and electrochemical properties have been reported all the ligands are weaker tt acceptors than bpy." " The crystal structures of... 

A study of fluorescence spectra provided no evidence to support a prediction that acid-base properties of indolizine in the first electronic excited state should differ from those in the ground state (69JCS(A)325>. 

Armarego109 has determined the pAa values of indolizines and aza-indolizines from their ultraviolet spectra. He found that indolizine itself has the same basic strength as a-naphthylamine (pAa 3.9) and that a methyl substituent increases the pAa by two to three units. Mason and Smith,110 studying the fluorescence spectra of various aromatic nuclei including indolizine, found no evidence to support the prediction that acid-base properties of aromatic hydrocarbons in the first electronic excited state should differ from those in the ground state. 

Abstraction, hydrogen atom, from O—H bonds, 9, 127 Acid-base behaviour macroeycles and other concave structures, 30, 63 Acid-base properties of electronically excited states of organic molecules, 12, 131 Acid solutions, strong, spectroscopic observation of alkylcarbonium ions in, 4, 305 Acids, reactions of aliphatic diazo compounds with, 5, 331 Acids, strong aqueous, protonation and solvation in, 13, 83 Acids and bases, oxygen and nitrogen in aqueous solution, mechanisms of proton transfer between, 22, 113... 

Ireland, J.F., Wyatt, P.A.H., "Acid-Base Properties of Electronically Excited States of Organic Molecules," Adv. Phys. Org. Chem., 1976,12, 131. 

Acid-Base Properties of Electronically Excited States of Organic Molecules... 

In view of the clear relationship between pX-changes and absorption spectra, a study of the influences of substituents and other consitutional changes upon such spectra has a very direct bearing upon the field of acid-base properties in excited states. For example, the —OH and —0 groups function as different substituents at the 2-position in naphthalene. Any theory which accounts for their different effects upon the naphthalene transitions therefore automatically also explains the change in the naphthol-naphtholate equilibrium upon excitation. The search for linear free energy relationships in electronic spectra will therefore continue to impinge upon this field. 

One common complication in flash photolysis studies is the production from the excited state of radicals which may be confused with or inhibit observation of the triplet state. The radical species, which usually has a longer lifetime than that of the triplet state, may be identified by separate experiments (Jackson and Porter, 1961) but such species may themselves show interesting acid base properties (e.g. Lindqvist, 1960 Lindqvist and Kasche, 1965 Simic and Hoffman, 1972 Neta, 1975). Their optical density contributions may therefore change with acidity in the range studied. 

Hc), triarylmethanols (HR), etc. Unfortunately these scales can differ by several units at the concentrated acid end. For recent reviews, the books by Rochester (1970) and Liler (1971) should be consulted. From the point of view of the acid-base properties of excited states the major question is therefore whether an Sj or Tj state of a substituted benzophenone, say, will behave like a ground-state benzophenone or like some other family of compounds with an electronic distribution, and hence polar character, rather more like that of the excited state in question. 

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