Ultrafast Fluorescence Photoswitch Incorporating Diketopyrrolopyrrole and Benzo[1,3]oxazine

With the objective of developing ultrafast fluorescent switch molecules, we have designed and synthesized fluorescence switch molecules incorporating two oxazine photochromes (OX) at the two end of single diketopyrrolopyrrole (DPP) fluorophore giving the shape of the dyad molecule as OX-DPP-OX. For precise characterization, steady-state photophysical properties, acid–base-induced spectroscopic studies and ultrafast transient absorption spectroscopic studies are performed. In acetonitrile (ACN) solution, the benzo[1,3]oxazine ring of studied oxazine derivatives in OX-DPP-OX opens up and reduces the fluorescence intensity of DPP by 66% upon addition of 50 equiv of trifluoroacetic acid (CF3COOH, TFA) and addition of an equivalent amount of base, tetrabutylammonium hydroxide ((C4H9)4NOH, TBAOH), closes the oxazine ring, reverting the fluorescence intensity of the DPP unit back to its original intensity. Likewise, upon 330 nm laser excitation, the oxazine ring opens up in less than 135 ps in ACN solution, redu...