New near-infrared absorbing conjugated electron donor–acceptor molecules with a fused tetrathiafulvalene–naphthalene diimide framework

Abstract

Molecular materials that can absorb and emit light in the near-infrared (NIR) region are attracting more and more attention in many fields. In this paper, we report the synthesis and studies of the photophysical and semiconducting properties of tetrathiafulvalene (TTF)–naphthalene diimide (NDI) fused molecules (NDITTF2, NDI2TTF and NDI2TTF3). The results reveal that all molecules show strong absorptions in the NIR region, and their absorption maxima can reach 1015 nm with molar extinction coefficients (ε) up to 66 900 M⁻¹ cm⁻¹ in the solution state. Moreover, NIR emissions were found for NDITTF2 and NDI2TTF either in solution or in the film state. The emission maxima in the CHCl₃ solution locate at 892 nm for NDI2TTF (ϕ = 1.64%) and 1062 nm for NDITTF2 (ϕ = 0.21%). Furthermore, the thin film of NDITTF2 was found to show p-type semiconducting properties with a hole mobility up to 0.45 cm² V⁻¹ s⁻¹.