The effect of TCNE and TCNQ acceptor units on triphenylamine-naphthalenediimide push-pull chromophore properties

Abstract

Asymmetrical and symmetrical push-pull chromophore-based on triphenylamine (TPA) donors and naphthalenediimide (NDI) acceptors are designed and successfully synthesized via [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction with well-known electron-accepting tetracyanoethylene (TCNE) and 7,7,8,8, -tetracyanoquinodimethane (TCNQ) groups. The novel series of compounds NDI-TPA-1 to NDI-TPA-6 were characterized to identify the influence of the TCNE and TCNQ Pi-conjugated linkers on the optical, electrochemical, and electronic properties of these molecules. We found that in dichloromethane the NDI-TPAs 1, 4, 5, and 6 display absorbance peaks at increasing wavelengths 605, 641, 646, and 645 nm, respectively. We demonstrated that through simple chemical modification we could drop the lowest occupied molecular orbital of NDI-TPA-1 to 6. Furthermore, NDI-TPA-1 to 6 were integrated into organic thin-film transistors (OTFTs) via spin-coating technique, and charge transfer properties were investigated. We found that the choice of the functional group led to either p-type, n-type, or ambipolar characteristics.