Electronic and Charge Transport Properties in Bridged versus Unbridged Nanohoops: Role of the Nanohoop Size

Abstract

AbstractIn the field of π‐conjugated nanohoops, the size of the macrocycle has a strong impact on its structural characteristics, which in turn affect its electronic properties. In this work, we report the first experimental investigations linking the size of a nanohoop to its charge transport properties, a key property in organic electronics. We describe the synthesis and study of the first example of a cyclocarbazole possessing five constituting building units, namely [5]‐cyclo‐N‐butyl‐2,7‐carbazole, [5]C‐Bu‐Cbz. By comparison with a shorter analogue, [4]‐cyclo‐N‐butyl‐2,7‐carbazole, [4]C‐Bu‐Cbz, we detail the photophysical, electrochemical, morphological and charge transport properties, highlighting the key role played by the hoop size. In particular, we show that the saturated field effect mobility of [5]C‐Bu‐Cbz is four times higher than that of its smaller analogue [4]C‐Bu‐Cbz (4.22×10−5 vs 1.04×10−5 cm2 V−1 s−1). However, the study of the other organic field‐effect transistor characteristics (threshold voltage VTH and subthreshold slope SS) suggest that a small nanohoop is beneficial for good organization of the molecules in thin films, whereas a large one increases the density of structural defects, and hence of traps for the charge carriers. The present findings are of interest for the further development of nanohoops in electronics.