Blue-LED Self-Assembly-Assisted Synthesis of New Photostable Organoboron Esters for Live-Cell Imaging

Abstract

In this work, we report a blue-LED self-assembly-assisted synthesis of novel emissive organoboron esters, achieved in just 30 minutes with quantitative yields. The molecular structure in solution (characterized by ¹H and ¹¹B NMR, and mass spectrometry) was further confirmed via X-ray molecular diffraction analysis for compound 3, where the boron ion adopts a distorted tetrahedral geometry. The photophysical properties of these molecules were analyzed in solution, revealing that 1, featuring tert-butyl groups and boron heterocycles with a nitro-substituent, exhibits superior photostability compared to its derivatives. Photobleaching values showed an inverse correlation with the oxidation potentials of compounds 1–3, except for 4, used as a reference. Mass spectrometry further revealed greater energetic stability of the molecular ion of 1. Notably, compound 3 demonstrated good solubility, high photostability, and adequate biocompatibility, making it a promising fluorescent dye for biomedical applications. Cytotoxicity assays in HEK-293 cells across different concentrations confirmed its non-toxic nature. Theoretical calculations further supported the high chemical stability of all compounds, attributing it to a synergistic interaction between electronic and steric effects, which protect the fluorophores by substitution of Schiff bases and formation of boron heterocycles. Additionally, 3 exhibited strong, non-hazardous blue fluorescence when tested on HEK-293 and MDA-MB-231 cells.