Highly fluorescent dihydropyrimido-diindole derivative as a probe for detecting nitrite in food products and cell-imaging

One-pot reaction approach to the synthesis of dihydropyrimido-diindole fluorophores (DPDI) was developed. In DPDI molecules, the two pyrrole rings in dipyrromethane were bridged by a carbon atom, eliciting a six-membered ring and rigid planar structure. Photophysical measurements demonstrated that DPDI can exhibit strong fluorescence, large Stokes shift and low sensitivity to pH. Cyclic voltamogram indicated a pair of redox peaks of DPDI near ±0.48V, implying that DPDI can be oxidized by nitrite (NO2−). In the presence of NO2−, DPDI showed apparent change in colours and fluorescence intensity owing to the implantation of NO2−. From this basis, a highly sensitive and selective analysis of NO2− was established using DPDI as probes, which offered a sensitive determination of NO2− in the concentration range of 0–17 μM with the detection limit of 2.2 nM. Furthermore, DPDI was employed for fluorescence imaging, demonstrating the ability to discriminate from different concentrations of NO2− in living cells. The newly developed DPDI dyes showed the obvious advantages of facile preparation and large Stokes shift over conventional dipyrrole-based phosphors.