Dicyanoquinodimethane (DCNQ) linked benzothiadiazole and phenothiazine derivatives for photoacoustic imaging

[Display omitted] •We designed and synthesized multifunctional D′-A′-A-π-D′ and D′-A′-D-π-D′ type donor–acceptor chromophores as suitable organic contrast agents for PA applications.•Two chromophores 3 and 4 exhibit an impressive photophysical properties due to cyano–based strong acceptor DCNQ unit.•3 and 4 gave PA signal > 700 nm, overlapping with their absorption, and detection limit 2 nmol/mL (in DMF). Photoacoustic imaging (PAI) is a non-invasive imaging procedure for application in e.g. oncology, rheumatology and cardiology due to its high sensitivity and deep tissue imaging ability. In PAI, organic chromophores and inorganic nanoparticles are the mainly used contrast agents, which exhibit an intense absorption spectra in the near infrared range (NIR, between 680 nm and 950 nm). Preferable are dyes with low to complete quenching of fluorescence emission. In this work, we present unsymmetrically configurated organic chromophores, D′-A′-A-π-D′ and D′-A′-D-π-D′ based on 2,1,3-benzothiadiazole (BTD) and phenothiazine as central core (A, D) units, which were modified with an additional acceptor (A′) dicyano quinodimethane (DCNQ), and donor (D′) triphenylamine. The bridging of DCNQ unit enable shifting the absorption spectra of the donor–acceptor based organic chromophores into the near infrared range, and quenches the fluorescence emission, thereby enhancing the PA signal gain. We postulate that such extended conjugated donor–acceptor systems can be tuned in versatile ways, for intensely absorbing, highly useful materials in medical diagnosis.