REPORTS 1938 Chinese Science Bulletin Vol. 48 No. 18 September 2003 Chinese Science Bulletin 2003 Vol. 48 No. 18 1938ü1942 Investigation of solvatochromism and aggregation behavior of C 60 (C 4 H 10 N + )I - in binary solvent mixtures WANG Guanwu 1 , HAO Erhong 1 , JIAO Lijuan 1 & YAN Lifeng 2 1. Department of Chemistry, University of Science and Technology of China, Hefei 230026, China; 2. Department of Chemical Physics, University of Science and Technol- ogy of China, Hefei 230026, China Correspondence should be addressed to Wang Guanwu (e-mail: gwang @ustc.edu.cn) Abstract Water-soluble N,N-dimethyl[60]fulleropyrro- lidinium iodide (C 60 (C 4 H 10 N + )I - ), when dissolved in binary mixtures of tetrahydrofuran and water, was found to exhibit remarkable solvatochromism. Correspondingly, the UV-vis spectra showed obvious changes by variation of the solvent composition of tetrahydrofuran and water. It was found that both concentration and temperature had strong influence on the stability of monomer-state C 60 (C 4 H 10 N + )I - , while they had little effect on the stability of aggregated C 60 (C 4 H 10 N + )I - . The formation of cluster was confirmed by TEM and AFM measurements. Keywords: N,N-dimethyl[60]fulleropyrrolidinium iodide, solvato- chromism, aggregation. DOI: 10.1360/03wb0061 Solvatochromism was observed in some solutions of C 60 or C 70 , which was thought to arise from the formation of fullerene clusters [1ü6] . This special type of solvato- chromism has aroused much interest because it has some potential applications in material science and sensor tech- nology. On the other hand, C 60 or C 70 can be made soluble in water by connecting it to various functional groups [7ü20] . Those functionalized fullerenes not only have been found a number of important applications in fields ranging from optical limiting to various topics in biological chemis- try [7ü11] , but also form ordered aggregate structures that can be utilized in material science [12ü20] . Fullerenes con- taining cationic or anionic group are water-soluble and are considered as a special kind of surfactant. Knowledge of the factors that govern the aggregate behavior of ionic fullerene derivatives is of considerable importance in evaluating the biomedical applications of these water- soluble compounds. Herein we report the solvatochro- mism and aggregate behavior of N, N-dimethyl[60] fulleropyrrolidinium iodide (C 60 (C 4 H 10 N + )I - ) in binary mixtures of tetrahydrofuran (THF) and water (H 2 O). 1 Experiment The title compound C 60 (C 4 H 10 N + )I - was synthesized according to the reported procedure, and its molecular structure was confirmed by its spectral data [21] . All organic solvents were redistilled before use. Doubly distilled wa- ter was used. Solutions of C 60 (C 4 H 10 N + )I - in binary mix- tures of THF and H 2 O were prepared by the following procedure. To an 100 mL volumetric flask containing 4.6 mg of C 60 (C 4 H 10 N + )I - , 50 mL of THF and then 50 mL of H 2 O were added, ultrasonicated for 1 min to afford trans- parent mother solution (5h10 -5 mol/L). A series of solu- tions (1h10 -5 mol/L) were obtained by diluting 5 mL of the mother solution to 25 mL with solvent mixtures of THF and H 2 O with appropriate volume ratios. The aque- ous solution of C 60 (C 4 H 10 N + )I - was prepared by the pre- viously described method [12,16] . UV-vis spectra were re- corded in a 10 mm path-length cell on a Shimadzu UV-2501 PC spectrophotometer. The sample for trans- mission electron microscopy (TEM, Hitachi H-800) was stained with uranyl acetate before it was set on carbon grids, followed by evaporation in vacuum. Atomic force microscopy (AFM) measurement was performed with a Nanoscope a multimode AFM controller (Digital In- struments, Santa Barbara, CA) for imaging. Commercially available silicon cantilever with 125 μm length was used for tapping mode AFM (model TESP, Digital Instruments). The sample was prepared by a spin-coater (KW-4A, Chemat Inc, China). 40 μL of sample solution was dropped on a new cleaved mica surface and spin-coated at 1800 r/s for 9 s and 5000 r/s for 30 s. 2 Results and discussion The solubility of C 60 (C 4 H 10 N + )I - in either THF or H 2 O is quite low. However, it has good solubility in the binary mixture of THF and H 2 O. A number of THF-H 2 O solutions of C 60 (C 4 H 10 N + )I - were prepared with different composition of THF and H 2 O. Interestingly, the solvato- chromism of C 60 (C 4 H 10 N + )I - could be observed by naked eyes. For the 1h10 -5 mol/L C 60 (C 4 H 10 N + )I - solutions, the color remained as pale pink until the water content reached 76%, and then changed dramatically to brown in a narrow range upon increasing the water content in solu- tion (Fig. 1). Similar color changes in DMF-H 2 O and DMSO-H 2 O binary systems, even though less obvious