Ratiometric discrimination of Th⁴⁺ ions by a fluorogenic quinoline appended phenanthridine sensor and its...

A new phenanthridine appended quinoline-based chemoreceptor 5-(5-(quinolin-8-yl)thiophen-2-yl)-tetrahydrodibenzo[a,i]phenanthridine (PHQBA) was successfully synthesized and characterized by ¹H, ¹³C, and HRMS spectral analyses. The promising chelation-induced process in PHQBA was accelerated by Th⁴⁺ ions, which impart robust ratiometric green fluorescence at 515 nm. The host-guest complex formed in a 1 : 1 binding stoichiometry between Th⁴⁺ ions and PHQBA was demonstrated by Jobs plot experiments. The Benesi-Hildebrand (BH) plot was employed to compute the binding constant for the complexation of PHQBA + Th⁴⁺, which was determined to be 3.77 × 10⁵ M^-1. To comprehend the detection mechanism of PHQBA, DFT, and TDDFT, eased computational studies were conducted and well supported by the experimental results. Moreover, the limit of detection (LOD) of PHQBA was determined as 223 nM, which defines the remarkable optical sensitivity of the sensor PHQBA. Further, portable paper strip detection and real-time determination of Th⁴⁺ ions in real water samples ensure the practical applications of PHQBA.