PHOTOPHYSICAL PROPERTIES OF C60H18 AND C60H36 - A LASER FLASH-PHOTOLYSIS AND PULSE-RADIOLYSIS STUDY

Spectroscopic and photophysical properties of two hydrogenated fullere nes, namely, C60H18 and C60H36, have been studied in benzene solution using laser flash photolysis and pulse radiolysis techniques..Samples of C60H18 and C60H36 used were prepared by the reduction of C-60 With Zn/concentrated HCl in benzene or toluene at normal (for C60H36) or at high (for C60H18) temperature and pressure. It is reported that C60H1 8 and C60H36 prepared by these methods have tetrahedral (T) symmetry c ontaining four highly delocalized benzenoid rings, and a crown structu re with C-3 upsilon symmetry, respectively. Owing to hydrogenation, th e fluorescence band of C-60 shifts toward the blue and both the fluore scence quantum yields and the singlet-state (S-1) lifetimes of the mor e hydrogenated species increase compared with those of the parent full erene molecule. Triplet quantum yields reduce considerably (e.g., phi( T) for C60H18 and C60H36 is 0.15 and 0.1, respectively) compared with unity for C-60 Also the singlet-singlet and triplet-triplet absorption spectra show considerable differences from those of C-60 Owing to suc cessive hydrogenation of C-60, the intensity of the near-IR band (at c a. 880 nm) in the singlet-singlet absorption spectra decreases and tha t in the visible (at ca. 500 nm) becomes more prominent. In the triple t-triplet absorption spectrum, the major band, which is seen at 740 nm for C-60, gradually shifts to the blue in the more hydrogenated speci es. The spectroscopic properties of the hydrogenated fullerenes used b y us have been seen to be different in many aspects compared with thos e reported by Bensasson et al. (Chem. Phys. 1997, 215, 111), possibly owing to the different symmetries of these derivatives prepared by dif ferent hydrogenation methods.