Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences , University of Groningen , Nijenborgh 4 , 9747AG Groningen , The Netherlands.
Chimie Et Interdisciplinarité, Synthèse, Analyse, Modélisation (CEISAM) , UMR CNRS no. 6230, Université de Nantes , BP 92208, 2, Rue de la Houssinière , 44322 Nantes Cedex 3, France.
J Phys Chem B. 2018 Jun 21;122(24):6423-6430. doi: 10.1021/acs.jpcb.8b03528. Epub 2018 Jun 11.
Spiropyrans undergo C-O bond breaking to their ring-open protonated E-merocyanine form upon protonation and irradiation via an intermediate protonated Z-merocyanine isomer. We show that the extent of acid-induced ring opening is controlled by matching both the concentration and strength of the acid used and with strong acids full ring opening to the Z-merocyanine isomer occurs spontaneously allowing its characterization by H NMR spectroscopy as well as UV/vis spectroscopy, and reversible switching between Z/ E-isomerization by irradiation with UV and visible light. Under sufficiently acidic conditions, both E- and Z-isomers are thermally stable. Judicious choice of acid such that its p K lies between that of the E- and Z-merocyanine forms enables thermally stable switching between spiropyran and E-merocyanine forms and hence pH gating between thermally irreversible and reversible photochromic switching.
螺吡喃在质子化和辐照时通过中间质子化 Z-硫代色烯异构体经历 C-O 键断裂，转化为其开环质子化 E-硫代色烯形式。我们表明，酸诱导的开环程度受所用酸的浓度和强度的控制，并且使用强酸会自发地完全开环到 Z-硫代色烯异构体，从而允许通过 H NMR 光谱和 UV/vis 光谱对其进行表征，以及通过用紫外线和可见光辐照进行 Z/E-互变异构的可逆切换。在足够酸性的条件下，E-和 Z-异构体都是热稳定的。明智地选择酸，使其 pK 介于 E-和 Z-硫代色烯形式之间，可在螺吡喃和 E-硫代色烯形式之间实现热稳定的切换，从而实现热不可逆和可逆光致变色切换之间的 pH 门控。
