Toward Fractioning of Isomers through Binding-Induced Acceleration of Azobenzene Switching

Abstract

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 H NMR investigations of the photochemical and thermal isomerization kinetics show that the thermal Z → E interconversion is 4-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 π* antibonding character. This results in a reduction of the N═N torsional barrier and thus in accelerated thermal Z → E isomerization. Combined with light-controlled E → Z isomerization, this enables controllable fractional tuning of the two configurational isomers.

Configurational Selection in Azobenzene‐Based Supramolecular Systems Through Dual‐Stimuli Processes

“…In 2017, our groups reported a detailed study on the E / Z isomerization process of the uracil‐azobenzene derivative 33 in which the nucleobase is conjugated to a phenyldiazene tail and on the effect of the formation of a triply H‐bonded complexes with a complementary 2,6‐diacetylamino‐4‐pyridine ligand (DAP, Figure ) Thanks to an accurate UV/Vis and 1 H‐NMR analysis all the relevant thermodynamic and kinetics parameters were determined.…”

Pyrazolylazophenyl Ether‐Based Photoswitches: Facile Synthesis, (Near‐)Quantitative Photoconversion, Long Thermal Half‐Life, Easy Functionalization, and Versatile Applications in Light‐Responsive Systems

“…[6] This has led to the discovery of af ew high-photoconversion azo switches with isomerization yields ! 90 %i nb oth directions [3,[7][8][9][10][11] (Table S1 in the Supporting Information) and several azo switches having very long-lived metastable isomers with t 1/2 values (25 8C) over am onth. [3, 4a, 7a, 8, 12, 13] (Table S2 in the Supporting Information) Nevertheless,t he integration of both high photoconversions and long t 1/2 into ap hotoswitchable molecular structure has posedar eal challenge in this field.…”

“…In the quest for improved photoswitch performance, continuous efforts have been devoted to the structural modification of azo compounds, for example tailoring the substituents on the azobenzene scaffold and replacing the traditional azobenzene structure with a heteroaromatic counterpart . This has led to the discovery of a few high‐photoconversion azo switches with isomerization yields ≥90 % in both directions (Table S1 in the Supporting Information) and several azo switches having very long‐lived metastable isomers with t 1/2 values (25 °C) over a month . (Table S2 in the Supporting Information)…”

Visible-light-responsive self-assembled complexes: improved photoswitching properties by metal ion coordination

“…[37] Protonation can also accelerate the Z®E thermal isomerization. [38] Hydrogen-bonded complexes have also been shown to accelerate Z®E isomerization, [39] while in other cases aggregation has slowed the Z®E isomerization time by two orders of magnitude. [40] Despite these examples, to the best of our knowledge the work here is the first where the rate of Z®E isomerization is decreased by coordination to transition metal ions, and offers a new method for controlling the photoswitching properties of azobenzenes.…”