Structure and Dynamics in Solvent-Polarity-Induced Aggregates from a C 60 Fullerene-Based Dyad S. Shankara Gayathri, Amit K. Agarwal, ‡ K. A. Suresh, ‡ and Archita Patnaik* , Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India, and Liquid Crystals Group, Raman Research Institute, Bangalore 560080, India Received August 24, 2005. In Final Form: September 23, 2005 A novel methanofullerene dyad based on a hydrophobic (acceptor C60 moiety)-hydrophilic (bridge with benzene and ester functionalities)-hydrophobic (donor didodecyloxybenzene) network is designed and synthesized. Electronic absorption spectral features revealed the molecule to exhibit a strong tendency to self-aggregate in binary solvent mixtures at room temperature, where the dielectric constant exceeds a critical value, ∼30. The dynamic structure factors of these spherical aggregates revealed stretched exponential decay with sizes varying between 110 and 250 nm with an increasing concentration, estimated from the dynamic light scattering experiments. However, a loss of shape selectivity of these aggregates was noted at lower water volume fractions in the binary solvent mixtures. The water-extracted spherical clusters were identified to be fractals with a dimension of 1.85, leading to diffusion-limited cluster aggregation as the mechanistic route for clusterization. Introduction A promising route to materials synthesis is the forma- tion and self-assembly of colloidal particles, which gives the opportunity to create highly ordered structures on length scales from nano- to micrometers. 1-6 In this context, Fullerene (C 60 ) has attracted a great interest not only for its promising applications but also for its unusual mo- lecular structure and truncated icosahedral symmetry. 7-9 Aggregation of C 60 has caused significant changes in its photochemical and photophysical properties, as compared to isolated molecules in solution; 10-12 one such example played a crucial role in the preparation of photovoltaic cells. 13 Thus, controlling the aggregation of C 60 in solution is of great importance for the development of functional materials. 8,14 It has been shown that there is no single solvent parameter that predicts in general the solubility of C 60 and that it usually dissolves in a solvent that has a large refractive index, a dielectric constant around 3-4, a large molecular volume, and a tendency to act as a moderate nucleophile. 9,15 C 60 aggregates have been extensively characterized in neat polar solvents and binary solvent mixtures, and the aggregation process has been largely determined by the polarity of the medium. 16 It is however difficult to control its structure because of the tendency of random aggregation in these solvents. 15 Thus, alterna- tive routes have been adopted to realize the aggregation of C 60 . Clusterization of C 60 has been observed by incorporating them into heterogeneous media such as micelles, 17 liposomes, 18 and vesicles. 19 Modification of the fullerene to be amphiphilic is one of the steps toward controlled aggregation through self-organization. Further, interesting biological activities of water-soluble fullerene derivatives have been discovered with an increasing interest in the preparation of aqueous solutions of fullerenes. 17,20-24 Several groups have reported the ag- gregation properties of the water-soluble C 60 derivatives, such as poly(ethylene oxide) (PEO), 1 acetyl carnitine, 5 bola amphiphiles, 25 etc. 2,21,26,27 Recently, our group has reported details of the aggregate structure and mechanism of * To whom correspondence should be addressed. Telephone: +91- 44-2257-4217. Fax: +91-44-2257-4202. E-mail: archita59@ yahoo.com. Indian Institute of Technology Madras. ‡ Raman Research Institute. (1) Song, T.; Dai, S.; Tam, K. C.; Lee, S. Y.; Goh, S. H. Langmuir 2003, 19, 4798-4803. (2) Zhang, P.; Li, J.; Liu, D.; Qin, Y.; Guo, Z.; Zhu, D. Langmuir 2004, 20, 1466-1472. (3) Alargova, R. G.; Deguchi, S.; Tsuji, K. J. Am. Chem. Soc. 2001, 123, 10460-10467. (4) Deguchi, S.; Alargova, R. G.; Tsuji, K. Langmuir 2001, 17, 6013- 6017. (5) Angelini, G.; De Maria, P.; Fontana, A.; Pierini, M.; Maggini, M.; Gasparrini, F.; Zappia, G. Langmuir 2001, 17, 6404-6407. (6) Martin, N.; Guldi, D. M. J. Mater. Chem. 2002, 12, 1978-1992. (7) Taylor, R.; Walton, D. R. M. Nature 1993, 363, 685-693. (8) Prato, M. J. Mater. Chem. 1997, 7, 1097-1109. (9) Dresselhaus, M. S.; Dresselhaus, G.; Eklund, P. C. Science of Fullerenes and Carbon Nanotubes; Academic Press: San Diego, CA, 1996. (10) Mohan, H.; Palit, D. K.; Mittal, J. P.; Chiang, L. Y.; Asmus, K.; Guldi, D. M. Faraday Trans. 1998, 94, 359-363. (11) Yevlampieva, N. P.; Biryulin, Y. F.; Melenevskaja, E. Y.; Zgonnik, V. N.; Rjumtsev, E. I. Colloids Surf., A 2002, 209, 167-171. (12) Guldi, D. M.; Prato, M. Acc. Chem. Res. 2000, 33, 695-703. (13) Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C. Adv. Funct. Mater. 2001, 11, 15-26. (14) Prato, M. Top. Curr. Chem. 1999, 199, 173-188. (15) Ruoff, R. S.; Tse, D. S.; Malhotra, R.; Lorents, D. C. J. Phys. Chem. 1993, 97, 3379-3383. (16) Nath, S.; Pal, H.; Palit, D. K.; Sapre, A. V.; Mittal, J. P. J. Phys. Chem. B 1998, 102, 10158-10164. (17) Hungerbuhler, H.; Guldi, D. M.; Asmus, K. J. Am. Chem. Soc. 1993, 115, 3386-3387. (18) Bensasson, R. V.; Bienvenue, E.; Dellinger, M.; Seta, S. J. J. Phys. Chem. 1994, 98, 3492-3500. (19) Janot, J. M.; Bienvenue, E.; Seta, P.; Bensasson, R. V.; Tome, A. C.; Enes, R. F.; Cavaleiro, J. A. S.; Camps, S. X.; Hirsch, A. Perkin Trans. 2000, 22, 301-306. (20) Isobe, H.; Nakamura, E. Acc. Chem. Res. 2003, 36, 807-815. (21) Samal, S.; Choi, B.; Geckeler, K. E. Chem. Commun. 2000, 1373- 1374. (22) Da Ros, T.; Prato, M. Chem. Commun. 1999, 663-669. (23) Dugan, L. L.; Turesky, D. M.; Du, C.; Lobner, D.; Wheeler, M.; Almli, C. R.; Shen, C. K. F.; Luh, T.; Choi, D. W.; Lin, T. Proc. Natl. Acad. Sci. U.S.A. 1997, 94, 9434-9439. (24) Sayes, C. M.; Fortner, J. D.; Guo, W.; Lyon, D.; Boyd, A. M.; Ausman, K. D.; Tao, Y. J.; Sitharaman, B.; Wilson, L. J.; Hughes, J. B.; West, J. L.; Colvin, V. L. Nanolett. 2004, 4, 1881-1887. (25) Sano, M.; Oishi, K.; Ishi-i, T.; Shinkai, S. Langmuir 2000, 16, 3773-3776. (26) Tan, C. T.; Ravi, P.; Dai, S.; Tam, K. C.; Gan, L. H. Langmuir 2004, 20, 9882-9884. 12139 Langmuir 2005, 21, 12139-12145 10.1021/la052313j CCC: $30.25 © 2005 American Chemical Society Published on Web 11/03/2005