Remote Control on the Photochemical Rearrangement of 1,6-(N-Aryl)aza-[60]fulleroids to 1,2-(N-Arylaziridino)-[60]fullerenes by N-Substituted Aryl Groups Akihiko Ouchi,* ,† Bahlul Z. S. Awen, † Ryota Hatsuda, † Reiko Ogura, ‡ Tadahiro Ishii, ‡ Yasuyuki Araki, § and Osamu Ito *,§ National Institute of AdVanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan; Faculty of Science, Tokyo UniVersity of Science, Kagurazaka, Tokyo 162-8601, Japan; and the Institute of Multidisciplinary Research for AdVanced Materials, Tohoku UniVersity, Sendai, Miyagi 980-8577, Japan ReceiVed: June 23, 2004; In Final Form: August 25, 2004 Photochemical rearrangement of 1,6-(N-aryl)aza-[60]fulleroids (1) to 1,2-(N-arylaziridino)-[60]fullerenes (2) depends on the N-aryl substituents remote from the reaction center. A systematic kinetic study of the N-substituents discloses a decrease in the reaction rates of the photochemical rearrangement in the order 1-naphthyl (1b) > 1-pyrenyl (1d) > phenyl (1a) > 2-naphthyl (1c). The large substituent effect in the rates, which vary by ca. 2200-fold, is interpreted in terms of changes in the reaction mechanisms. The fast photochemical rearrangement of derivatives 1b,d proceeds through the normal triplet states of 1; in the case of 1b, triplet sensitization by the product 2b also operates. For the slow rearrangement rates of 1a,c, nanosecond transient absorption spectroscopy reveals that different triplet states participate, namely, electron transfer between the N-aryl substituent and the fullerene. Introduction In recent years, chemical modification of C 60 became increas- ingly important as a tool for the functionalization of fullerenes to add new functions to the parent fullerene molecules. Many thermal and photochemical reactions have been developed for the efficient chemical modification of fullerenes. 1,2 One of the widely used reactions is that of fullerenes with organic azides, 3,4 which has been extensively employed for the preparation of functional fullerene derivatives 5 and for the incorporation of fullerenes into various polymers. 6 Both thermal and photo- chemical processes have been reported for this reaction. For C 60 molecules, the thermal reaction proceeds by initial 1,3- dipolar cycloaddition of the azide to the double bonds of C 60 , followed by nitrogen elimination to form 1,6-(N-substituted)- aza-[60]fulleroids (1), 3 whereas the photochemical reaction proceeds by the initial generation of nitrenes and their addition to the double bonds of C 60 to form 1,2-(N-substituted-aziridino)- [60]fullerenes (2). 3 The photochemical conversion 1 f 2 (Scheme 1) is also often used in the chemical modification of C 60 , 3-6 but the details on the scope and limitations of this reaction are not known. A spectroscopic study of 1 and 2 with alkyl substituent, e.g., the methoxyethoxymethyl (MEM) group, has been conducted, and an interaction between the electron pair of the nitrogen atom and the fullerene π-electron system was found. 7 If the interaction between the nitrogen atom and the C 60 moiety of 1 and 2 is due to the nitrogen electron pair, a similar reactivity would be expected for the photochemical rearrangement 1 f 2, regardless of the type of N-substituents used. Nonetheless, a striking effect of the N-substituent has been reported in the photochemical rearrangement, e.g., whereas 1,6-(N-methoxyethoxymethyl)aza- [60]fulleroid (1, Ar ) MEM) is photochemically inactive, 3c 1,6- (N-phenyl)aza-[60]fulleroid (1a) rearranges photochemically into 2a. 3g This result indicates additional features that play an important role in the photochemical reactivity of 1. Although photochemical rearrangements of the carbon analogues, i.e., fulleroids to methanofullerenes, 8 have been carried out, sys- tematic studies on the substituent effects of the bridged carbon atom have not been reported so far. This remote control of the reaction is most likely due to interactions between the N-aryl substituents that are not directly connected to the reaction center and the C 60 moiety. For this reaction to be useful in the preparation of novel materials, it is necessary to understand the nature of this remote controlling effect of the N-substituted aryl groups. If the photochemical properties of the fullerene derivatives may be manipulated by appropriate N-substituents, such fullerene derivatives may find valuable applications in material science. Therefore, we have conducted a systematic study on the photochemical rearrangement 1 f 2 with different N-aryl substituents (Scheme 1), 9 namely, the phenyl (a), 3g 1-naphthyl (b), 2-naphthyl (c), and 1-pyrenyl (d) groups. Indeed, the difference in the photochemical rearrangement rates was found to be more than 2000-fold between the fastest (1b) and slowest (1c). This rate effect is attributed to switching between two † National Institute of Advanced Industrial Science and Technology (AIST). ‡ Tokyo University of Science. § Tohoku University. * Corresponding author. E-mail: ouchi.akihiko@aist.go.jp. SCHEME 1 9584 J. Phys. Chem. A 2004, 108, 9584-9592 10.1021/jp0472717 CCC: $27.50 © 2004 American Chemical Society Published on Web 10/08/2004