Toward fractioning of isomers through binding-induced acceleration of azobenzene switching

R. Vulcano, P. Pengo, S. Velari, J. Wouters, A. De Vita, P. Tecilla, D. Bonifazi
J. Am. Chem. Soc., 2017, 139, 50, 18271-18280
DOI: 10.1021/jacs.7b09568


The E/Z isomerization process of a uracil-azobenzene derivative in which the nucleobase is conjugated to a phenyldiazene tail is studied in view of its ability to form triply-H-bonded complexes with a suitably complementary 2,6-diacetylamino-4-pyridine ligand. UV-Vis and 1H-NMR investigations of the photochemical and thermal isomerization kinetics show that the thermal ZE interconversion is four-fold accelerated upon formation of the H-bonded complex. DFT calculations show that the formation of triple H-bonds triggers a significant elongation of the N=N double bond, caused by an increase of its πg antibonding character. This results in a reduction of the N=N torsional barrier and thus in accelerated thermal ZE isomerization. Combined with light controlled EZ isomerization this enables controllable fractional tuning of the two configurational isomers.

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