Synthesis of novel chiral oligothiophenes showing outstanding chiroptical properties in thin films

Chirality in organic optoelectronics is a topic which is rapidly gaining interest:1 it is one of the most sophisticated expedients to control the supramolecular order of π-conjugated molecules constituting the active layers of devices,2 also opening the way to innovative applications, such as producing (CP-OLED),3 or detecting (CP-OFET)4 circularly polarized (CP) light or sensors specifically responding to enantiomers.5 In this field, a very intriguing research topic is to obtain thin films with high discrimination of CP-light in absorption (electronic circular dichroism, ECD) and in emission (circularly polarized luminescence, CPL). Chiral supramolecular architectures of π-conjugated oligomers can be an efficient approach to achieve this goal. Therefore, we developed the synthesis of new oligothiophenes (Figure 1a) functionalized with inexpensive alkyl chiral groups from natural sources (i.e. (S)-3,7-dimethyl-1-octyl and (S)-2-methyl-1-butyl chains), investigating their optical and chiroptical features in thin films depending on the deposition technique (drop casting or spin coating).6 Some of them revealed the uncommon property of ECD spectrum inversion by sample flipping (Figure 1b): this behaviour, which we called LDLB effect, is theoretically well understood but to date only rarely reported in the literature. Interestingly, it could find very appealing application, implying the possibility to discriminate the direction of sample illumination, if from front or from back.