Synthesis and photoinduced electron transfer processes of rotaxanes bearing [60]fullerene and zinc porphyrin: effects of interlocked structure and length of axle with porphyrins.

Three rotaxanes, with axles with two zinc porphyrins (ZnPs) at both ends penetrating into a necklace pending a C60 moiety, were synthesized with varying interlocked structures and axle lengths. The intra-rotaxane photoinduced electron transfer processes between the spatially positioned C60 and ZnP in rotaxanes were investigated. Charge-separated (CS) states (ZnP*+, C60*-)rotaxane are formed via the excited singlet state of ZnP (1ZnP*) to the C60 moiety in solvents such as benzonitrile, THF, and toluene.

Photoinduced intramolecular electron-transfer processes in [60]fullerene and N,N-Bis(biphenyl)aniline molecular systems in solutions.

Photoinduced intramolecular charge-separation and charge-recombination processes in covalently connected C(60)-(spacer)-bis(biphenyl)aniline (C(60)-sp-BBA) and C(60)-((spacer)-bis(biphenyl)aniline)(2) (C(60)-(sp-BBA)(2)) have been studied by time-resolved fluorescence and transient absorption methods. Since a flexible alkylthioacetoamide chain was employed as the spacer, the folded structures in which the BBA moiety approaches the C(60) moiety were obtained as optimized structures by molecular orbital calculations. The observed low fluorescence intensity and the short fluorescence lifetime of the C(60) moiety of these molecular systems indicated that charge separation takes place via the excited singlet state of the C(60) moiety in a quite fast rate and high efficiency even in the nonpolar solvent toluene, which was a quite new observation compared with reported dyads with different spacers.

Photoinduced intramolecular electron-transfer processes in [60]fullerene-(Spacer)-N,N-bis(biphenylyl)aniline dyad in solutions.

Intramolecular photoinduced charge-separation and charge-recombination processes in a covalently connected C60-(spacer)-N,N-bis(biphenylyl)aniline (C60-spacer-BBA) dyad, in which the center-to-center distance of the electron acceptor and electron donor is 15 A, have been studied by time-resolved fluorescence and transient absorption methods. The observed low fluorescence intensity and the short fluorescence lifetime of the C60 moiety of the dyad in PhCN and THF indicate that charge separation takes place via the excited singlet state of the C60 moiety at a quite fast rate and a high efficiency. The nanosecond transient absorption spectra in PhCN and THF showed the broad absorption bands at 880 and 1100 nm, which were attributed to C60(*-)-spacer-BBA(*+).

Prolongation of the lifetime of the charge-separated state at low temperatures in a photoinduced electron-transfer system of [60]fullerene and ferrocene moieties tethered by rotaxane structures.

A rotaxane tethering both fullerene (C60) and ferrocene (Fc) moieties (abbreviated as (C60;Fc)rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C60;Fc)rotax+, the C60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C60 and Fc in (C60;Fc)rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity.