J. Phys. Chem. 1995,99, 15955-15962
15955
Solvent Effects on the Absorption Maxima of Fullerenes CSOand c70 Indrek Renge institute of Physics, Estonian Academy of Sciences, EE2400 Tartu, Estonia Received: February 2, 1995; In Final Form: June 23, 1995@
Absorption spectra of fullerenes CWand C70 have been recorded between 200 and 700 nm in liquid n-alkanes at room temperature. Solvent shifts ( - p ) of band maxima vary from 900 cm-' (the 636 nm band in c70) to 18 000-19 000 cm-' (the 209 nm band in c 6 0 and the 210 nm band in c70) per unit Lorentz-Lorenz function r$(n2)= (n2 - l)/(n2 2), where n is the refractive index at the Na D line. Changes of static polarizabilities (ha)have been calculated from the Bakhshiev formula by equating the Onsager cavity radii to 0.75 and 0.8 nm for C, and c70, respectively. The estimated A a values lie in the interval between 10 and 15 A3 for weak transitions (400-650 nm) and reach magnitudes as high as 150-200 As for the strongest transitions at 210 nm. The dispersive shift of the equally intense 256 nm band in C a and 235 nm band in c70 yields A a values of 41 f 2 and 79 f 10 A3, respectively. Allowed transitions between 300 and 400 nm possess a relatively small solvent shift and Aa: -p = 2000-2500 cm-' and A a = 20-25 A3. Published values of absorption and fluorescence maxima in cold jets, vapors, solid inert gases, solvent and polymer glasses, and doped and neat crystals have been plotted as a function of r$(n2). A purely thermal bathochromic shift of 50-100 cm-' between low (4-77K) and ambient temperatures could be established for 620, 404 (C,), and 636 nm $70) bands. The large bandwidth of allowed transitions(
