Circular Dichroism Imaging: Mapping the Local Supramolecular Order in Thin Films of Chiral Functional Polymers

We introduce the concept of circular dichroism (CD) imaging CDi, which is made possible by the use of the highly collimated light beam of synchrotron radiation (SR) only available at Diamond Light Source B23 beamline for surface scanning of solid samples. At the moment, the space resolution is about 1 mm2, but there are prospects to increase it to at least 0.1 mm2 in the near future. We apply SR-CDi to thin films of conjugated polymers, which give rise to large chiral aggregates. Electronic CD is able to reveal and characterize these supramolecular structures; thus, SR-CDi provides the ultimate complement to microscopy for investigating local domains with different molecular order and to fill a gap between a purely morphological knowledge and an intimate insight into the molecular level. As a corollary of this proof-of-concept work, we showed that such a new technique may provide rational and successful protocols to obtain homogeneous active layers for the fabrication of optoelectronic devices.