Computational design of two-photon fluorescent probes for intracellular free zinc ions

Two-photon fluorescence probes used in two-photon fluorescence microscopy (TPM) can achieve intact tissue imaging without destruction. Therefore, for a long time, TPM has been an important tool in biology and medicine. In this background via a quantum chemical method, a series of zinc ion probe molecules using N,N-di(2-picolyl)ethylenediamine (DPEN) as the recognition group were studied, which are based on the photoinduced electron transfer (PET) mechanism. The fact that the one-photon absorption peak is almost unchanged and the fluorescence emission intensity increased significantly upon coordination with a zinc ion reveals that these probes can be PET fluorescent bioimaging reagents. And it is predicted that when the chemically modified probe molecule is incorporated with Zn²⁺, the two-photon absorption (TPA) cross-section (δ_max) will greatly increase and the TPA peak will be in the near-infrared region. The molecules after changing the fluorophore become more suitable for probing Zn²⁺ in vivo, and a modification at the end of the fluorophore can fine-tune the fluorescence and TPA properties. The detailed investigations will provide a theoretical basis for synthesizing new zinc-ion-responsive two-photon fluorescent probes.