SYNTHESIS AND ELECTRONIC-PROPERTIES OF C-60-O-QUINODIMETHANE ADDUCTS

Several C-60-o-quinodimethane adducts having various aromatic rings ha ve been synthesized by the simple thermal reaction of C-60 with dihydr ocyclobutaarenes. According to MM2 calculations, the most stable confo rmation of the cyclohexene ring in these adducts is not the half-chair , but the half-boat. On the basis of variable temperature NMR results, its inversion rate was found to depend on the attached aromatic rings , mainly due to the steric effect. The absorption spectra in the visib le region were substantially identical for all the adducts, exhibiting a weak and broad band around 700 nm with vibrational structures. The fluorescence spectra due to the C-60 moiety of the adducts were also s imilar to each other and independent of the excitation wavelength. The fluorescence excitation spectra were in good agreement with the corre sponding absorption spectra. No fluorescence could be observed from th e attached aromatic rings even in the case of pyrene, because of the q uenching by the intramolecular S-1(pyrene)-S-0(C60) energy transfer. T he similar transient -S absorption spectra of the C-60 adducts were as cribed to the T-n-->T-1 absorption of the C-60 moiety. These results s how that little intramolecular electronic interaction between the C-60 and aromatic moieties takes place in the adducts.