Outstanding chiroptical features in thin films of chiral π-conjugated oligomers: from synthesis to applications

Chirality is gaining large interest in organic optoelectronics: first, it is a valid tool for controlling the supramolecular order of π-conjugated systems constituting the active layer of devices; secondly, it opens the way to innovative technological applications, like detecting or producing circularly polarized (CP) light. A current research goal is to obtain thin films of organic semiconductors with high discrimination of CP-light in absorption (electronic circular dichroism, ECD) or emission (circularly polarized luminescence, CPL). Chiral supramolecular architectures of π-conjugated systems could be the key to achieve this goal. In the present doctoral work, we developed a family of novel chiral π-conjugated oligomers functionalized with inexpensive alkyl chiral groups from natural sources, studying their ECD and CPL features in thin films. Since special care should be taken, in order to avoid the occurrence of false signals, here we provided practical tools for recognizing, quantifying and possible separating the main contributions of experimental ECD and CPL spectra. Although in general we observed a manifold of situations, thus revealing the central role of different local supramolecular structures (whose formation is strictly related to chemical structure, deposition technique and post-deposition operations), in some cases we discovered outstanding chiroptical features. Encouraged by promising results, for some of them we finally explored the application as active layers in circularly polarized organic light-emitting diode (CP-OLED) devices.