Unveiling the Roles of Aromaticity on Optoelectronic and Charge-Transport Properties of Dehydrobenzo[n]annulenes

Abstract

Dehydrobenzo[n]annulenes ([n]DBA) are a family of π-conjugated shape-persistent macrocycles, whose properties are governed by both their arylene groups and alkynylene linkages. While diverse members of [n]DBAs have been extensively studied, the triacetylene-bridged [24]DBA, a missing member, remained elusive. Herein, we report the first synthesis of a hexa-n-dodecyloxy-substituted [24]DBA using Sonogashira cyclotrimerization of an in-situ generated triyne intermediate. For comparison, the other three [n]DBA derivatives (n = 12, 18 and 30) were also synthesized using modified literature procedures. Comprehensive structural characterization by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry and single-crystal X-ray diffraction analysis unambiguously confirm the planar geometry of [n]DBA cores and sheet-like two-dimensional packing in the solid state. This complete series of [n]DBA enables an exploration of their ring-size-dependent optoelectronic and charge-transport properties. 1H NMR analysis disclose an alternating behaviour between aromaticity and antiaromaticity with increasing core size. UV-vis absorption and fluorescence measurements also reflect an alternation between broad and narrow energy gaps. Moreover, space-charge-limited current (SCLC) measurements demonstrate that antiaromatic [n]DBA (n = 12 and 24) derivatives exhibit higher hole mobilities than their aromatic counterparts (n = 18 and 30). The successful synthesis of [24]DBA not only fills a critical gap in the [n]DBA family, but also establishes a structure-property relationship for designing π-extended [n]DBA derivatives with enhanced charge transport.