Hetero-donors-adorned anthraquinones with near infra-red absorption for solution-processable photodetectors

We introduce a donors-acceptor-based molecular design strategy of organic heteroaromatic compounds with enhanced photosensitivity in the ultraviolet (UV)/visible/near-infrared (NIR) regions. Three organic dyes are meticulously designed and synthesized, involving various donor (D) moieties and the anthraquinone acceptor (A) unit, following the so-called quasi-orthogonal A-D-D' architecture. The target compounds are synthesized via the Buchwald-Hartwig cross-coupling reactions, with the yields of up to 54 %. The molecular structure of the synthesized compounds is confirmed by a combination of experimental and theoretical methods. Density functional theory (DFT) calculations are performed for geometry optimization and analysis of the vibrational normal modes. The time-dependent calculations (TD-DFT) reveal a manifold of intramolecular charge-transfer (ICT) states with various degrees of the central D donor involvement and the local excitation (LE) admixtures. The lowest S1 state of the ICT nature (D' → A) provides the weak absorption in the near IR region. The TD-DFT calculation affords interpretation of the UV-visible-NIR absorption spectra as well as photoconductivity of the fabricated diodes, which includes ICT complexes of the studied compounds with the known triphenylamine derivative (TCTA). Implementation of the semiconductor monolayer of the molecular mixture of A-D-D' type compound and TCTA allows to obtain the high-performance near-infrared organic photodetectors.