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ABSTRACT Complex formations in C60 solutions have previously been observed in diethylanilineI. In a wide survey of solvents conducted in our laboratory, several additional solvents exhibited complexing behavior with C60 when analyzed with UV-Vis and fluorescence spectroscopy. 2 All solvents with complexing behavior contained nitrogen. They are benzonitrile, N-methylpyrrolidone, and triphenylamine. A careful study was done to characterize the formation of the complexes formed in C60/toluene solutions when each complexing agent was added. Diethylaniline was added to the study as a reference complexing system. Formation of the complexes was followed with UV-Vis and fluorescense spectroscopy. Nash plots of the complexes were done to determine the equilibrium constant and the isosbestic point for each system. Nonlinear optical characterization of the complexing solvents was analyzed. INTRODUCTION We have investigated optical limiting, 3,4,5 nonlinear absorption, 6 and photoluminescence of C60 in a variety of solvents. 2 ,7 Expanding the useful list of solvents for C60 in nonlinear optic applications has led us to investigate the behavior of C60 in complexing solvents. Complex 89 formation has been observed in many aliphatic and aromatic amines. 14 Initial observations of complex formation were documented in several broad studies on solvent effects. 2 ,10,11 We report here the comparison of C60 complexes in toluene and methylcyclohexane with aromatic amines DEA, BZN, NMP, and TPA. Nonlinear absorption measurements for complexes formed in toluene are reported and analyzed with respect to the complex concentration and ground and excited state modeling. RESULTS AND DISCUSSION Materials C60 (99.99% pure) was purchased from MER Corp. and used as received. Toluene (HPLC) grade) , methylcyclohexane, diethylaniline (DEA), benzonitrile (BZN), N-methylpyrrolidone (NMP), and triphenylamine (TPA) were purchased from Aldrich Chemical Co. and used as received. Filtered (.2 g PTFE) stock solutions of C60/toluene (9.32 x 10-4 M) and C60 /MCH (4.79 x 10-5 M) and saturated solutions of TPA/toluene(.61 M), and TPA/MCH (.30 M) were prepared. Experimental Stock solutions of C60 in MCH and toluene were doped with varying amounts of each complexing agent and examined using UV spectroscopy. UV spectra were taken on a Perkin Elmer Lambda 9, and fluorescence spectra were taken using a Perkin Elmer LS5 lB. Broadening 299

Mat. Res. Soc. Symp. Proc. Vol. 374 ©1995Materials Research Society

of the spectra and the appearance of isosbestic points indicative of complex formation in a 1:1 stoichiometric ratio 12 were observed for DEA, BZN, TPA and toluene in C60/MCH solutions. Similar results were seen in C60/toluene solutions for DEA, BZN, NMP, and TPA. Evaluation of the equilibrium constant (K) was calculated from Nash plots 13 whose linear fit shows 1:1 complex formation. 14 Table I shows the measured K values, and location of the isosbestic points for each system. Table I. Equilibrium Constants and Isosbestic Points for Complex Systems Solvent Sys