Cyclodextrins modify the proton transfer photoreactions of norharmane

Excited state proton transfer reactions of norharmane have been investigated in the presence of cyclodextrins (CDs): β-CD and modified β-CDs at pH values of 4.0, 7.8, 10.0 and 13.0. The spectral shape and the species present in the equilibria depend on the CDs and the pH of the media. Thus at pH 4.0 the emission corresponds to the cationic form. At pH 7.8 the emission spectra show the bands corresponding to the cationic and neutral forms in the case of the complexes with β-CD and HPβ-CD, and only the neutral band for the complexes of DMβ-CD and TM β ˜ CD. At pH 13.0 all the complexes exhibit the neutral form together with the zwitterionic one. The low polarity environment afforded by CDs significantly alters the proton transfer photoreaction of norharmane. The titration curves obtained for the complexes with NaOH or HCl are related to the shifts in the acid–base equilibria in excited states.