FLUORESCENCE EMISSION AND CONFORMATION OF -ALPHA-(1-NAPHTHYLMETHYL)-2,3-DI-O-PENTYLCELLULOSE IN DILUTE-SOLUTION

The fluorescence property and molecular structure of a specifically su bstituted cellulose derivative, -alpha-(1-naphthylmethyl)-2,3-di-O-pen tylcellulose (NPeC), were investigate d. Steady-state and time-resolve d measurements of fluorescence spectra were carried out for a dilute s olution of NPeC in tetrahydrofuran at different temperatures. It was f ound that the cellulose derivative forms a naphthyl excimer intramolec ularly via a dynamic process requiring quite a small activation energy (E(a) = 2.8 kcal mol(-1)). The intramolecular excimer formation in NP eC is interpreted as a consequence of the short-range approach of two adjacent naphthyl chromophores after photoexcitation of one of them; p ossibly, the substituents are originally allowed to be fairly close to each other, owing to a special arrangement of the carbohydrate backbo ne. In combination with the conformational analysis performed on a mod el disaccharide as a dimer unit of NPeC, it is suggested that the back bone chain of this polymer prefers to assume a ''twisted'' structure.