Abstract
The first in-depth, systematic study of the photoswitching properties of Donor-Acceptor Stenhouse Adducts (DASAs) is reported. Barbituric acid derived DASAs functionalised with 14 different amines ranging from dimethylamine to 4-methoxy-N-methylaniline were structurally characterised in solution using 1H and 13C NMR spectroscopy and, in eight cases, in the solid state by single crystal X-ray diffraction. The distribution of coloured and colourless isomers in the dark, their photostationary states under irradiation, apparent thermal half-lives, and fatigue resistance are systematically compared. A simple kinetic model is used to characterise photoswitching behaviour and reveals that minor structural modifications can significantly improve the photoswitching properties of DASA photochromes. These modifications result in excellent photoswitching properties for '1st generation' DASAs in chloroform, including exceptional fatigue resistance, opening the door for these photochromic molecules to find widespread applications.
Highlights
Photochromic molecules[1] can be isomerised between two different forms upon irradiation with light
Except 14, has a similar absorption maximum in chloroform indicating the electronic transition responsible for driving the isomerisation is essentially identical for the series
Donor–acceptor Stenhouse adducts (DASAs) 1–8 are all derived from secondary alkyl amines and were expected to function
Summary
Photochromic molecules[1] can be isomerised between two different forms upon irradiation with light. Considering the remaining DASAs, the equilibrium for the rst step in the light (kl1/klÀ1) shows that this step is strongly favoured (kl1/klÀ1 $ 100) for 1, 9, 11 and 14 and these are the switches with amongst the greatest changes in absorption at PSS (94, 96, 99 and 99% bleached respectively).
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