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

In 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. Experimental/theoretical investigations link the size of a nanohoop to its charge transport properties, which are key in organic electronics. the first cyclocarbazole possessing five constituting building units was synthesized and studied. Comparison of the photophysical, electrochemical, morphological and charge transport properties with those of a shorter analogue highlights the key role played by the hoop size. Corresponding cycloparaphenylenes with eight and ten phenyl units were also compared. Notably the saturated field effect mobility of the five‐unit cyclocarbazole is four times higher than that of its smaller analogue.