Tuning Optical, Electrical and Solid-State Structures of Oligothiophenes by Introduction of Di- and Tricyanovinyl Groups

The presence of dicyanovinyl (DCV) and tricyanovinyl (TCV) groups in oligothiophene molecules imparts several interesting characteristics. They allow oligothiophenes to act as an acceptor in donor-acceptor systems, which is particularly useful in the design of organic electronic materials. They also result in shifting the absorption properties of the molecule, often leading to a bathochromic or red shift in the absorbance, which allows the compound to absorb and emit light at longer wavelengths. These groups also affect the redox characteristics of the molecule, which can be observed through cyclic voltammetry. The shape and polarity of the di- and tricyanovinyl groups can influence the solid-state packing of these molecules, affecting their charge transport properties which are crucial for applications in organic semiconductors. These groups are readily introduced and in the case of EDOT render the molecules more stable and less susceptible to oxidation and polymerization. We summarize our work on 16 thiophene derivatives endowed with one or two DCV and/or TCV groups. We highlight and summarize the impact of these groups on the above-mentioned characteristics. The molecules include: 2T-TCV; 2T-DCV; Br-2T-TCV; FUSED 2T-DCV; DCV-T-DCV; DCV-2T-DCV; DCV-3T-DCV; 3T-TCV; EDOT-TCV; Br-EDOT-TCV; T-CH=CH-T-TCV; Bu2T-CH=CH=T(Bu2)-TCV; TOLYL-3T-TCV; NC-Ph-T-Ph-CN; O2N-2T-NO2. Our results suggest that these groups profoundly impact the electrical, optical and packing and both the molecular geometries and solid-state structures of oligothiophenes. Specifically, they induce planarity, bathochromic shifts, pi stack formation and ease of both oxidation and reduction. All these are thought of as favorable properties for optical, electrical and optoelectronic properties of oligothiophenes. We assume that similar properties can impact other conjugated organic materials. We briefly describe our success with triphenylamines and fused TCNQ-like molecules.