Fluorescent Molecular Rotors of Organoboron Compounds from Schiff Bases: Synthesis, Viscosity, Reversible Thermochromism, Cytotoxicity, and Bioimaging Cells

Abstract

We report the design, synthesis, and characterization of two new fluorescent molecular rotors of boron derived from Schiff bases: (2,4,8,10-tetra-tert-butyl-6-phenyldibenzo[d,h][1,3,6,2]dioxazaboronine (3) and 1,4-bis(2,4,8,10-tetra-tert-butyldibenzo[d,h][1,3,6,2]dioxazaboronin-6-yl)benzene (4), as well as the free ligand 2-[[(3,5-di-tert-butyl-2-hydroxyphenyl)imino]methyl]-4,6-di-tert-butylphenol 1. All compounds were fully characterized by NMR (H, B, andC), IR, UV/vis, fluorescence spectroscopy, and high-resolution mass spectrometry. The crystal structures of 3 and 4 showed tetracoordinated boron atoms with semiplanar skeleton ligands. The free rotation of the fluorescent molecular rotor, only observed in the binuclear compound, was decreased with increasing viscosity, while the quantum yield was increased. Interestingly, the property of reversible thermochromism was found in organoboron 4 in the solid state. DFT calculations to determine the both complexes have free rotation around the CPh-B1 bond. The boron compounds 3 and 4 have shown low cytotoxicity activity in cell line A-431 and low green staining in cells.

Synthesis and Characterization of the Hemi‐Salen Ligands and Their Triboron Complexes: Spectroscopy and Examination of Anticancer Properties

“…Jímenez‐Pérez et al . synthesized a series of fluorescent molecular rotors of organoboron compounds from Schiff bases and studied their viscosity, reversible thermochromism, cytotoxicity, and bioimaging cells . Akkaya and co‐workers prepared a new dimeric BODIPY dye with reduced symmetry, which is ineffective as a photosensitizer unless it is activated by a reaction with intracellular glutathione as differential enhancement of photocytotoxicity targeting of cancer cells .…”

Fluorescent boron Schiff bases dyes for staining silk fibroin: Green synthesis, structural characterization, DFT, and photophysical properties

“…Complexes 1 – 5 are soluble in ethyl acetate, chloroform, and CH 2 Cl 2 . The microwave‐assisted synthesis, resulted to be ten times faster and cheaper than the traditional solution via …”

Two‐Photon Detection of Organotin Schiff Base Complexes in Cancer Cells

“…Fluorescent properties can be sensitive to pH and to other external factors such as viscosity and temperature . Recently, biologically‐active compounds derived from Schiff base molecules have shown promise as fluorescent reporters . These molecules possess the azomethine fragment (−N=CH), which is the key to the design of new drugs with anti‐convulsant, anti‐depressant, analgesic, anti‐inflammatory, and anti‐malarial activity.…”