Abstract
Chiral molecules exist as pairs of nonsuperimposable mirror images; a fundamental symmetry property vastly underexplored in organic electronic devices. Here, we show that organic field-effect transistors (OFETs) made from the helically chiral molecule 1-aza[6]helicene can display up to an 80-fold difference in hole mobility, together with differences in thin-film photophysics and morphology, solely depending on whether a single handedness or a 1:1 mixture of left- and right-handed molecules is employed under analogous fabrication conditions. As the molecular properties of either mirror image isomer are identical, these changes must be a result of the different bulk packing induced by chiral composition. Such underlying structures are investigated using crystal structure prediction, a computational methodology rarely applied to molecular materials, and linked to the difference in charge transport. These results illustrate that chirality may be used as a key tuning parameter in future device applications.
Highlights
Chirality is a fundamental symmetry property, which manifests across multiple length scales, from elemental particles, to molecules and even macroscopic objects, such as human hands
Chirality has been used as a structural probe, where the assembly and aggregation of device-relevant chiral π-conjugated small molecules or polymers have been studied using highly sensitive chiroptical spectroscopy.13−15 We previously reported the use of enantiopure 1-aza[6]helicene, an intrinsically helical organic semiconductor, in the production of organic photoFETs which could detect and differentiate circularly polarized (CP) light
Monolayers of a number of helicenes have been studied on a range of metallic surfaces, and it has been shown that their chirality is central to the 2D structures obtained.20−27 Coupled with the device compatibility of aza[6]H,7,16 we reasoned that a helicene would provide an excellent representative chiral organic semiconducting (OSC)
Summary
Chirality is a fundamental symmetry property, which manifests across multiple length scales, from elemental particles, to molecules and even macroscopic objects, such as human hands. Chirality has been used as a structural probe, where the assembly and aggregation of device-relevant chiral π-conjugated small molecules or polymers have been studied using highly sensitive chiroptical spectroscopy.− We previously reported the use of enantiopure (single handed) 1-aza[6]helicene (aza[6]H, Figure 1), an intrinsically helical (and chiral) organic semiconductor, in the production of organic photoFETs which could detect and differentiate circularly polarized (CP) light.16 This effect was a result of the known strong chiroptical properties of this class of molecules, where left- or righthanded aza[6]H preferentially absorbs left- or right-handed CP light and mediates a selective photoresponse. On the basis of these results, we believe that chiral composition could be a useful means to control the macromolecular organization and electronic properties of (black text) and aged (blue text) devices
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