A flexible polycyclic chemosensor for simultaneous discernment of Ni2+ and Cd2+ depending on distinct coordination modes

Herein, we present a paradigm of a flexible molecular system for simultaneous discernment of Ni²⁺ and Cd²⁺, depending on distinct chemical coordination manners. By incorporating two functional pyridine groups at different positions on the flexible DPAC framework (9,14-diphenyl-9,14-Dihydrodibenzo [a,c]phenazine), two derivatives are prepared as 27Py-DPAC and 36Py-DPAC. The results show that 27Py-DPAC can chemically coordinate with Ni²⁺ (intermolecular coordination) and Cd²⁺ (intramolecular coordination), generating fluorescence turn-off and -on behaviors, respectively. The key factors leading to the different coordination ways are the ionic radius and the substituted positions of pyridine groups. Demonstrably, 36Py-DPAC can respond to Ni²⁺ abiding by the principle of the 27Py-DPAC sensor, but it cannot sense Cd²⁺ because of the difficulty in forming an effective intramolecular coordination resulted from the large distance between two nitrogen atoms on pyridine and the central heterocyclic ring. Based on the ionic response properties of the two compounds, logic circuits were developed to simulate logical operations and facilitate ion detection. This research expands the applicability of flexible polycyclic conjugated molecules in chemical sensing and underscores the influence of different modification sites of functional groups on ion binding mechanisms.