Phenothiazine Based Donor-Acceptor Compounds with Solid-State Emission in the Yellow to NIR Region and Their Highly Selective and Sensitive Detection of Cyanide Ion in ppb Level.

Four new novel donor-acceptor (A-π-D-A, A-D-π-D-A) compounds (1 a, 1 b, 2 a and 2 b) based on ethylenedioxythiophene (EDOT) and phenothiazine (PTz) have been rationally designed and synthesized towards solid state emission ranging from yellow to near infrared (NIR). The compounds 1 b and 2 b, in thin film form, showed an emission maximum at 713 nm and 696 nm, respectively, with the corresponding absolute solid-state quantum yield of 3.3 % and 9.0 %. The fluorophores showed high emission in the doped state as well when dispersed in polystyrene (PS) matrix with emission maximum ranging from 536 nm to 648 nm with quantum yield in the range 12.4 %-64.4 %. The presence of dicyanovinyl (DCV) group in both the fluorophores was exploited towards cyanide sensing in DMSO leading to turn-on fluorescence emission with high selectivity and sensitivity for cyanide ion with a detection limit of as low as 0.32 µm (8 ppb) for 1 b and 0.57 µm (14 ppb) for 2 b. DFT and TTDFT calculations suggested that the addition of cyanide ion prevented the intramolecular charge transfer (ICT) from the donor (PTz or EDOT) to acceptor (DCV), thereby turning the fluorescence "On". Using fluorescent spectral and color switching, we have explored logic gates with single and two input signal amplification by applying chemical and light inputs in the form of CN- ion and UV.