TY - JOUR

T1 - Azo-hydrazone molecular switches

T2 - Synthesis and NMR conformational investigation

AU - Kurutos, Atanas

AU - Kamounah, Fadhil S.

AU - Dobrikov, Georgi M.

AU - Pittelkow, Michael

AU - Sauer, Stephan P. A.

AU - Hansen, Poul Erik

PY - 2021/10/4

Y1 - 2021/10/4

N2 - A series of five intramolecularly hydrogen-bonded arylhydrazone (aryl = phenol, p-nitrophenol, anisole, quinoline) derived molecular switches have been synthesized and characterized by NMR and HRMS techniques. It was found that the compounds exist as different isomers in solution. An investigation of both conformational and/or configurational changes of the azo-hydrazone compounds was carried out by 1D 1H- and 13C- spectra, 2D NOESY, COSY, HSQC and HMBC techniques. It was found that these stimuli-responsive molecular switches exist mainly in the E form by intramolecularly hydrogen-bonded between NH and the pyridine nitrogen at equilibrium. Deprotonation of the neutral E form yields the E’ deprotonated isomer. Prediction of 13C-NMR chemical shifts was achieved by DFT quantum mechanical calculations. Anions have traditionally been difficult to calculate correctly, so calculations of the anion using different functionals, basis sets and solvent effects are also included. Deuterium isotope effects on the 13C-NMR chemical shifts was employed in the assignments and furthermore utilized as indicators of intramolecular hydrogen bonding. Studies in various organic solvents including CDCl3, CD3CN and DMSO-d6 were also performed aiming to monitor dynamic changes over several days. The effect of the hydrogen bonded solvents leads to Z-forms.

AB - A series of five intramolecularly hydrogen-bonded arylhydrazone (aryl = phenol, p-nitrophenol, anisole, quinoline) derived molecular switches have been synthesized and characterized by NMR and HRMS techniques. It was found that the compounds exist as different isomers in solution. An investigation of both conformational and/or configurational changes of the azo-hydrazone compounds was carried out by 1D 1H- and 13C- spectra, 2D NOESY, COSY, HSQC and HMBC techniques. It was found that these stimuli-responsive molecular switches exist mainly in the E form by intramolecularly hydrogen-bonded between NH and the pyridine nitrogen at equilibrium. Deprotonation of the neutral E form yields the E’ deprotonated isomer. Prediction of 13C-NMR chemical shifts was achieved by DFT quantum mechanical calculations. Anions have traditionally been difficult to calculate correctly, so calculations of the anion using different functionals, basis sets and solvent effects are also included. Deuterium isotope effects on the 13C-NMR chemical shifts was employed in the assignments and furthermore utilized as indicators of intramolecular hydrogen bonding. Studies in various organic solvents including CDCl3, CD3CN and DMSO-d6 were also performed aiming to monitor dynamic changes over several days. The effect of the hydrogen bonded solvents leads to Z-forms.

KW - Faculty of Science

KW - azo-dyes

KW - Molecular switches

KW - isotope effect

KW - 1H-NMR

KW - 13C-NMR

KW - 2D-NMR

KW - DFT

KW - Density functional theory

KW - computational chemistry

U2 - 10.1002/mrc.5164

DO - 10.1002/mrc.5164

M3 - Journal article

C2 - 33860564

VL - 59

SP - 1116

EP - 1125

JO - Magnetic Resonance in Chemistry

JF - Magnetic Resonance in Chemistry

SN - 0030-4921

IS - 11

ER -