A theoretical investigation and design of fluorescent probes with large two-photon absorption cross-sections and dual signaling behavior for mercury ions in biological system

In the present study, we have designed a series of novel two-photon mercury ion (Hg²⁺) fluorescent probes with large two-photon absorption cross-sections (δ_max) based on intramolecular charge transfer (ICT), and carried out the quantum-chemical calculations on the electronic structural and two-photon absorption (TPA) properties of these probes. The calculated results reveal that the fluorescent peaks of the reaction products with Hg²⁺ display significant red-shifts compared with these corresponding Hg²⁺ probes, demonstrating that these two-photon Hg²⁺ probe molecules can be applied as excellent ratiometric fluorescent bio-imaging reagents. More importantly, some designed molecules possess large δ_max values (1000–3100 GM) in the near-infrared region (650–1100 nm), which can be viewed as more promising candidates for detecting Hg²⁺ in the vivo biological system. Furthermore, we hope the investigations can provide a theoretical basis for developing novel two-photon fluorescent Hg²⁺ probes in the biological system.