Enhancement of Photodriven Charge Separation by Conformational and Intermolecular Adaptations of an Anthracene–Perylenediimide–Anthracene Triad to an Aqueous Environment

Photoinduced electron-transfer dynamics of an electron donor–acceptor–donor triad, consisting of anthracenes and perylenediimide (An 2 PDI), were investigated in different media by using time-resolved laser spectroscopic techniques. The aromatic components are attached by flexible linkers containing hydrophilic quaternary ammonium joints in the triad. In MeOH, in which An 2 PDI dissolves completely, no electron-transfer products were observed in the transient absorption measurements after the excitation of anthracenes and PDI because of the rapid back-electron transfer. The charge-separation rate of the triad in MeOH was estimated as 1.2 × 10 10 s –1 from the quenching of the singlet-excited state of PDI. In contrast, the formation of electron-transfer products was evident in water, and the electron-transfer rate was 200 times faster than the rate in MeOH in the course of the excitations of the selected components of An 2 PDI (2.5 × 10 12 s –1 ). It is concluded from the time-resolved data that the conformational disposition of the hydrophilic joints due to hydrophilic–lipophilic interactions and the facile π-stacking of hydrophobic PDI cores in water results in the contraction and the relative rigidity of the electron-transfer distance and the intermolecular stabilization of electron-transfer species within the polymeric self-assemblies of An 2 PDI, enabling an efficient photodriven electron-transfer process to occur.