Spectroscopic studies of purines—iv. polatization of emission from purine and some of its derivatives*

— The polarization of fluoresecnce and phosphorescence due to the emission from (π,π*)singlet and triplet states of purine and several of its derivatives have been measured using the method of photoselection. In at least two 2-amino substituted derivatives, the two lowest π-π* transition moments are mutually perpendicular. The main vibrational progression of phosphorescence is negatively polarized with respect to both of them and therefore must be singlet states interact with the emitting (π.π*) triplet state. In addition a weak progression, polarized in the plane of the molecule, is found. The vibronic mixing of (n,π*) and (π,π*) triplet states is suggested to account for the mixed polarization. The halogen derivatives of purine show zero plarization of phosphorescence and their phosphorescence spectra are blurred so that it is difficult to differentiate the various interacting states.