Excited-state acidity carbazole

In some cases, data obtained through the Forster cycle show similar inconsistencies, depending on whether absorption or emission is used. It may well be that either the equilibrium structure in the excited state is very different from the unrelaxed Franck-Condon one, or that 0-0 frequencies are too poorly estimated. It seems, therefore, that the most reliable results are those generated by method (3). This method has been applied to the study of carbazole (3) acidity in its S, state (85MI5). 

In the second step the reaction is less efficient because of quenching of the excited state of the diphenylamine component by the adjacent carbazole. Other cyclisations such as the conversion of (41) into (42) by irradiation in acetic acid have also been reported. As mentioned earlier cw-azobenzene derivatives cyclise under conditions where the nitrogens are protonated or complexed. A series of heavily substituted azobenzenes has been shown to undergo photochemical cyclodehydrogenation on irradiation in methylene dichloride solution with added SnCU- The reaction has been shown to be an efficient path to the heavily methylated cinnolines in good yield. 

The acidity constants of carbazole, 2-nitrocarbazole, 2-methoxycarbazole, and 3-methylcarbazole in the ground as well as in the lowest excited singlet state have been measured <2000JML33>. 

Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds. Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2-iV,A -dimethylaminopyridine induced by p-nitroaniline is also caused by exciplex formation. The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons. The A -isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.Photoinduced electron-transfer in the p-phenylenediamine-paraquat complex yields the paraquat cation. ... 

For this work we chose groups which could be excited to the triplet state easily. One was the carbazole moiety. The second was acridone. Both have acidic NH groups which can be used to attach them to the appropriate side chain. 

---