Torsional Influences within Disordered Organic Electronic Materials Based upon Non-Benzenoid 1,6-Methano[10]annulene Rings

Abstract

Conjugated polymers and small molecules containing the nonplanar aromatic 1,6-methano[10]annulene were synthesized in an effort to understand how torsional differences between planar and nonplanar π-electron components influence the electronic properties of π-conjugated materials. The polymers and small molecule model systems contain commonly employed aromatic subunits such as thiophene, diketopyrrolopyrrole, and 2,1,3-benzothiadiazole, leading to electron donor and donor–acceptor polymers. The curved geometry of 1,6-methano[10]annulene can lead to reduced local torsional strain in semiconducting polymers relative to large planar aromatics, potentially increasing intrapolymer conjugation. The relative amount of effective conjugation length increase granted by the annulene in each system of regioisomers was interrogated through the use of UV–vis and photoluminescence spectroscopy and electrochemistry, and it was found that 1,6-methano[10]annulene relieves some torsional strain associated with solubilizing alkyl chains clashing with aromatic rings along the polymer backbone. The polymers were also found to be highly disordered in thin films yet still provided reasonable hole mobilities (ca. 10–4 cm2/(V s)) in OFET devices. These results suggest that methano[10]annulene or other curved aromatics may prove useful in the future development of organic electronics.