Photoinduced shuttling movement

Figure 6.8 Structural formula of the rotaxane 96+ and schematic representation of the intramolecular (below left) and sacrificial (below right) mechanisms for the photoinduced shuttling movement of macrocycle between the two stations A1 and A2.

The strategy devised in order to obtain the photoinduced shuttling movement of R between the two stations Ai + and A2 + is based on a four stroke synchronized sequence of electron transfer and molecular rearrangement processes, as illustrated in Figure 27(b).Light excitation of the photoactive unit P + (process 1) is followed by the transfer of an electron from this unit to Ai + (process 2) which competes with the intrinsic decay of the P + excited state (process 3). After the reduction of Ai +, with the consequent deactivation of this station, the ring moves (process 4) by 1.3 nm to encircle A2 +, a step that is in competition with the back electron transfer from Ai+ (still encircled by R) to the oxidized unit P + (process 5). Eventually, a back electron transfer from the free reduced station Ai + to the oxidized unit P + (process 6) restores the electron-acceptor power to this radical cationic station. As... 

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