Photochemical Synthesis of Polyrotaxanes from Stilbene Polymers and Cyclodextrins

Abstract

COMMUNICATIONS mononuclear fragment [Eq. (2)] should be competitive with dimerization to form [CU,L,]~+. For neocuproine, this is a highly favorable process and is only slightly less propitious for L'. Formation of the 1/2 complex is not so auspicious with L2, presumably because of steric crowding, and there is a serious drop in stability constant for this step. Metallohelicate assembly, following coordination of a second copper(1) center [Eq. (3)], is considerably easier with the more flexible bipyridylbased ligand than with its phenanthroline analogue. In part, this difference can be attributed to the relative capacity for internal rearrangement to provide a suitable binding geometry around the cation. It is during addition of the second copper(1) cation that the real differences emerge between the two multitopic ligands. It appears that L' exhibits positive cooperativity towards copper(1) in that K , < K, < K3 and the overall stability constant for the metallohelicate (lgp, = 26) compares well with the only available published data for a somewhat comparable proc e s~. [ '~] In the case of L2, helicate formation is not driven by positive cooperativity since K2 < K , < K 3 , and the overall stabil-

Polyrotaxanes

“…On the contrary, Wenz and his co-workers (112) reported that the linear polymer with stilbene units formed hetero polypseudorotaxanes with β-and γ-CD by adding stilbene. Moreover, they successfully obtained interlocked hetero polyrotaxanes with βand γ-CD by photoirradiation (112). Tetraphenylcyclobutane blocking groups along the polymer main chain have been formed by UV irradiation in the presence of β-and γ-CDs (Fig.…”

Polyrotaxanes and Polycatenanes: Recent Advances in Syntheses and Applications of Polymers Comprising of Interlocked Structures

“…However, several problems have remained, e.g., how to control and read molecular motions. Shigekawa and Komiyama et al have nicely demonstrated that the selected a-cyclodextrin ring(s) of one of Harada s polyrotaxanes is(are) reversibly shuttled using scanning tunneling microscope (STM) technique [117]. The group showed three modes of shuttle manipulation, i.e., simple shuttling of a ring, pair-shuttling of two adjacent rings, and bending.…”

Cyclodextrin Polymers

“…The solubility of the host/ guest complex in water is due to a partial coverage of the polymer chain by the host; the cyclodextrin rings preferably occupy the alkyl segments rather than the poly(oxyethylene) segments [127]. An interesting photochemical capping method with stilbene segments of a stilbene copolymer-based rotaxane was reported [128]. Poly(azomethynes) photoconductors have been included in -or -CyD and capped with N-butyl carbazole [129].…”