A novel phenanthridine and terpyridine based D-π-A fluorescent probe for the ratiometric detection of Cd in environmental water samples and living cells.

A "turn-on" Donor-π-Acceptor (D-π-A) containing phenanthridine-functionalized extended π-conjugate terpyridine, 5-(4'-([2,2':6',2''-terpyridin]-4'-yl)-[1,1'-biphenyl]4-yl)7,8,13,14-tetrahydrodibenzo [a, i] phenanthridine (TBTP) was synthesised. It shows strong selectivity for the detection of toxic Cd without interference from other metal ions. In the presence of Cd, the absorption of the TBTP changes dramatically along with the fluorescent emission with the large Stokes shift of 6300 cm. When the compound TBTP is exposed to UV light, its colour changes from blue to orange over the addition of Cd. Adding other transition metal ions has no effect. This is based on the mechanism of intramolecular charge transfer. The detection limit for Cd was found to be around 1.181 × 10 M. An investigation of the sensing mechanism includes job plot, NMR titration, DFT calculation, and HRMS analyses. Excitingly, the recognition of Cd in CHCN: HO (8:2, v/v) medium is quantitative without interference from Zn which is a common interferent for Cd. Furthermore, the probe was used for detecting Cd in real water samples and cell imaging in living cells was also performed.