Construction of an orthogonal ZnSalen/Salophen library as a colour palette for one- and two-photon live cell imaging

Abstract

Construction of a colour palette based on modular "core" dyes with tuneable emission and tailor-made intracellular localization is of importance to visualize and distinguish different organelles and even observe their intracellular cross-talking. However, due to lack of structural information linking photophysical properties and the specificity of subcellular localizations, the modification of photophysical properties cannot always enable tailor-made specificity. In this work, we report the construction of a ZnSalen/Salophen library (48 examples) and study the one-and two-photon optical properties, lipophilicity and subcellular distribution of the complexes. Experimental and theoretical studies demonstrate that changes of the electronic states of the diamine moieties are effective for modulation of the photophysical properties of the ZnSalen/Salophen complexes. On the other hand, the subcellular localization is highly related to the lipophilicity of the ZnSalen/ZnSalophen complexes, which is correlated to the functionalization of the N-substitutients at the 4-position. Thus, the orthogonality between the photophysical properties and the subcellular localizations of the ZnSalen/Salophen complexes, regulated by discrete moieties (diamines and salicylaldehydes), renders them suitable fluorophores for the modular design of bioprobes in live cell imaging. More importantly, to demonstrate their potential application, we applied these Zn complexes as a colour palette for multicolour imaging in live cells using one-and two-photon fluorescence microscopes.

A Cryptand-Type Aluminum Tris(salophen) Complex: Synthesis, Characterization, and Cell Imaging Application

“…The two main absorption bands at near 300 and 400 nm can be assigned to salophen-centered π-π* transitions. Different from the previously reported Zn salen complexes [17,21,31], no intramolecular charge-transfer transition bands between 500-600 nm is observed for there is no "D-π-A" structure in the salophen ligands. The absorption peaks of LAl 3 red-shifts ca.…”

“…In our group, a series of Zn salen/salophen complexes have been reported as fluorescent probes for cell imaging even with super-resolution, with multiple functions such as intracellular reactive oxygen species, monitoring the lipid droplets and autophagy processes [17][18][19][20][21][22][23]. However, Zn salen complexes tend to aggregate through the axial intermolecular interactions between the Zn center and the phenolic oxygen of another molecule, especially in non-coordinating solvents [24][25][26][27][28][29].…”

Two-photon luminescent metal complexes for bioimaging and cancer phototherapy

“…32) as a color palette for one-and two-photon live cell imaging [235]. The d 10 metal Zn(II) is a bioavailable metal widely found in metalloenzymes [236].…”

Introducing Metallosalens into Biological Studies: The Renaissance of Traditional Coordination Complexes

“…Through the construction of a fluorescent Zn(salen) library of 48 complexes, the relationship between the molecular structures, the photophysical properties, and the subcellular distribution of Zn(salen)s were carefully studied . Experimental and theoretical results demonstrated that changes in the diamine moieties could effectively modulate the photophysical properties of the Zn(salen)s. The subcellular localizations were strongly related to the lipophilicity, which is correlated to the N‐substituents at the 4‐position of the salicylaldehyde motifs (Figure ).…”