A theoretical investigation on two latest two-photon pH fluorescent probes

• This contribution theoretically confirmed PCT and PET probe mechanism.
• An effective way for designing of large TPA cross-section PCT probe is provided.
• The replacement of fluorophores to improve the two-photon response is feasible in PET probe.

Intracellular pH plays critical roles in cell, enzyme, and tissue activities, including proliferation and ion transport, and muscle contraction. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, investigations on two-photon fluorescent probes are very rare. In this work, we thoroughly study two latest two-photon pH fluorescent probes and design two excellent two-photon pH fluorescent probes. One-photon properties of these pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated by using the DALTON program. The calculated results indicate that the designed CAE-CN can serve as a proper Photoinduced Charge Transfer two-photon pH fluorescent probe and the designed AP1 can serve as a proper Photoinduced Electron Transfer two-photon pH fluorescent probe.