Selective photoinduced charge separation in perylenediimide-pillar[5]arene rotaxanes

Abstract

The ability to control photoinduced charge transfer within molecules represents a major challenge requiring precise control of the relative positioning and orientation of donor and acceptor groups. Here we show that such photoinduced charge transfer processes within homo- and hetero-rotaxanes can be controlled through organisation of the components of the mechanically interlocked molecules, introducing alternative pathways for electron donation. Specifically, studies of two rotaxanes are described: a homo[3]rotaxane, built from a perylenediimide diimidazolium rod that threads two pillar[5]arene macrocycles, and a hetero[4]rotaxane in which an additional bis(1,5-naphtho)-38-crown-10 (BN38C10) macrocycle encircles the central perylenediimide. The two rotaxanes are characterised by a combination of techniques including electron diffraction crystallography in the case of the hetero[4]rotaxane. Cyclic voltammetry, spectroelectrochemistry, and EPR spectroscopy are employed to establish the behaviour of the redox states of both rotaxanes and these data are used to inform photophysical studies using time-resolved infra-red (TRIR) and transient absorption (TA) spectroscopies. The latter studies illustrate the formation of a symmetry-breaking charge-separated state in the case of the homo[3]rotaxane in which charge transfer between the pillar[5]arene and perylenediimide is observed involving only one of the two macrocyclic components. In the case of the hetero[4]rotaxane charge separation is observed involving only the BN38C10 macrocycle and the perylenediimide leaving the pillar[5]arene components unperturbed.

Oligothiophene‐Ring‐Strapped Perylene Bisimides: Functionalizable Coaxial Donor–Acceptor Macrocycles

“…In this case, the rise times were found to be enhanced from TSP1 to TSP2 , as well as their recovery dynamics. These growth time scales necessarily signify the charge separation process ( τ CS ) [52, 57–60] . From the multiexponential fitting, charge separation processes were found to be occurring on a time scale of 1.8 ps ( k CS ≈0.5×10 12 S −1 ) and 3.1 ps ( k CS ≈0.3×10 12 S −1 ) for TSP1 and TSP2 , respectively.…”

“…However, the positive features in TSP1 and TSP2 are quite broad and very different from the rPBI positive signature. This must originate from the formation of PBI radical anion in the macrocycle system (Figure S17) [57–60] …”

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

“…83 A hetero[4]rotaxane consisting of one crown ether and two pillar[5]arene macrocycles, and perylenediimide diimidazolium axle was recently reported by Champness and coworkers. 84 The hetero[4]rotaxane showed photoinduced charge separation between crown ether macrocycle and the perylenediimide, which are different from a homo[3]rotaxane consisting of the same axle and two pillar[5]arene macrocycles (without the crown ether macrocycle).…”

Donor-Acceptor Dyads and Triads Employing Core-Substituted Naphthalene Diimides: A Synthetic and Spectro (Electrochemical) Study

“…In particular, we are interested to investigate whether the properties of donor and acceptor influence each other, or if the components act independently. With this aim in mind, we have been studying the class of acceptor molecules based on naphthalenetetracarboxylic diimides (NDIs) and their analogues [1][2][3][4].…”