Positional Isomeric Thiophene-Based π-Conjugated Chromophores:Synthesis,Structure,and Optical Properties

A series of positional isomeric chromophores o-TC,m-TC,and p-TC,in which electron-rich thiophene moieties were connected byπ-conjugated bridges,were divergently synthesized and characterized.Single-crystal X-ray diffraction analysis revealed an intriguing zipper-like packing mode which was adopted by m-TC in the solid state.Subsequently,UV−vis absorption spectra and fluorescence spectra in a series of solvents were investigated.The nearly coplanar para isomer p-TC was found to have the most intense UV−vis absorption,fluorescence emission,and the highest photoluminescence quantum yield.The molecule structure,electronic nature,and origination of the absorption of p-TC were revealed through density functional theory calculations.Interestingly,all three positional isomers exhibited strong and stable electrochemiluminescence emission,which enriched the existing knowledge on the optical properties of thiophene-based oligomers.

Effective assignment of positional isomers in dimeric shikonin and its analogs by ^(1)H NMR spectroscopy

An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with ^(4)JC,H long-range correlation by prolonging the acquisition time at ^(2,3)JC,H values of 2.0 and 8.0Hz.Furthermore,the ^(1)H(proton)nuclear magnetic resonance(NMR)pattern of phenolic hydroxyl protons was developed as a“diagnosis signal”to ascertain the relative location of each side chain in DMSO-d_(6) at sample concentrations of 0.022-0.034 mol/L.The chemical shift differences of 0.6ppm between OH-5' and OH-1 and between OH-8'and OH-4 are assigned to Type A and Type B,respectively.All reported ambiguous structures were corrected by this pattern.Additionally,the steric structures of isolated compounds were elucidated by quantum chemical calculations of electronic circular dichroism(ECD)spectra.

A novel on-tissue cycloaddition reagent for mass spectrometry imaging of lipid C=C position isomers in biological tissues

Application of matrix-assisted laser desorption/ionization mass spectrometry imaging(MALDI-MSI) to investigate the spatiotemporal alterations of lipids in biological tissues has brought many significant results.However, the presence of structural isomers varying in C=C double bond(DB) locations makes isomerresolved MSI an urgent need. Herein, we introduce a new type of light-driven on-tissue [2 + 2] cycloaddition reaction coupled with MALDI-MS/MS imaging to identify lipid DB position isomers and their spatial signatures in biological tissues. 3-Benzoylpyridine was introduced as a novel derivatization reagent, and it exhibited great reactivity toward lipid C=C bond to form oxetanes under both ultraviolet light and visible light irradiation. With this approach, DB position isomers of lipids were imaged with highly differential levels in distinct regions of rat brain, providing an accurate and spatially resolved approach to study tissue lipidomics.