| Abstract: | The fluorescence of ortho-hydroxycinnamic acid was studied in aqueous solution over the pH 0-14 range and in methanol. At pH values above 9.7, intense anion fluorescence is observed. In the pH 4-9 range emissions are from both the monoanion (albeit weakly) and from the dianion due to photodissociation. In the pH 0-4 range a blue and a green fluorescence was found, which is attributed to emissions from the unchanged molecule and from an unusual excited state tautomer respectively. The latter is assumed to be the phenolate anion of cinnamic acid and represents a tautomer with no equivalent in the electronic ground state. It is assumed to be formed by adiabatic photodissociation during the lifetime of the first excited singlet state. |
