Planar Chiral Charge-Transfer Cyclophanes: Convenient Synthesis, Circularly Polarized Light-Responsive Photothermal Conversion and Supramolecular Chiral Assembly.

Abstract

We report herein a series of macrocycles in which the densely π-stacked charge-transfer (CT) donor/acceptor with naphthalenediimides (NDIs) or perylene diimide (PDI) as acceptor moiety pairing various donor moieties are locked by covalent bond. The X-ray crystallography of C8BDT-NDI reveals a short intramolecular π-stacking distance around 3.4 Å and the existence of intermolecular donor/acceptor π-stacking (3.7 Å). The intramolecular CT is highly dependent on the electron-donating ability of donor moiety and replacing carbazole (C8KZ) with benzo[1,2-b:4,5-b']dithiophene (C8BDT) or dihydroindolo[3,2-b]indole (C8DN) redshift CT absorption into NIR region. Notably, both C8BDT-NDI and C8DN-NDI demonstrate excellent photothermal performance, which is a result of the active non-radiative pathways. Interestingly, the different molecular symmetry between donor and acceptor moiety in cyclophanes endow C8BDT-NDI and C8DN-NDI with intrinsic planar chirality. The enantiomeric C8BDT-NDI shows chiral selectivity for incident light, i.e., when irradiated by left-circularly polarized light, (R)-C8BDT-NDI is more sensitive and a higher maximum stable temperature is achieved. While, enantiomeric C8DN-NDI pack with different orientations forming M- and P-handedness helix, respectively, demonstrating molecular planar chirality being transferred and amplified through molecular assembly. These results provide insight into the intramolecular charge transfer in enforced D/A π-stacks in which CT interactions and planar chirality would be engineered through structural control.