NMR studies of the polyphotochromic behaviour of biphotochromic compounds

Abstract

NMR spectroscopy has been used to investigate the photochromism of four biphotochromic molecules in both the spirooxazine and naphthopyran families. The thermal evolution of photoproducts and their structural identification made it possible to observe polyphotochromic behaviour: photocoloration, thermal bleaching, photo and thermal isomerisation, photoelectrocyclisation and thermochromism.

A New Approach for Studying Bond Rupture/Closure of a Spiro Benzopyran Photochromic Material: Reactivity Descriptors Derived from Frontier Orbitals and DFT Computed Electrostatic Potential Energy Surface Maps

“…Recently, there has been an exponential growth of interest in photochromism for profitable applications in important technologies [1][2][3][4][5][6][7][8][9][10][11][12][13]. Spiropyrans are one of the major classes of organic photochromes [2,3].…”

“…The photochromism of the spiropyran/trans-merocyanine pair has been reviewed previously [3]. The rate and mechanism of the reaction of some spiropyrans and their analogues in different media have been examined with different spectroscopic techniques [4][5][6][7][8][9][10][11][12][13][14]. Spiropyran photoisomerization was studied using ion mobility-mass spectrometry and three major conformers were identified.…”

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

“…The stilbene etheno bridge, however, may also lead to an intricate photochromic behavior as it can undergo isomerization and cyclization reactions. For example, the irradiation of a 5'-naphthylvinyl-substituted spirooxazine derivative led not only to a ring opening of the oxazine unit but also to an irreversible loss of the photochromic properties, resulting from a cyclization-oxidation reaction under aerobic conditions [51][52][53]. In this context, we were interested in the effect of a positively charged arylvinyl substituent on the photochromic properties of the spironaphthoxazine.…”

Photochromic Spirooxazines Functionalized with Oligomers: Investigation of Core−Oligomer Interactions and Photomerocyanine Isomer Interconversion Using NMR Spectroscopy and DFT

“…Spirooxazines absorb UV light, which results in the cleavage of the spiro C-O bond in the oxazine ring, leading to the planar photomerocyanine forms (Scheme 1) of which there are 8 possible isomers and 2 dominant isomers as determined by NMR, the most prominent of which is shown in Scheme 1. 13,14 The use of NMR to characterize spirooxazines and their photoproducts is well established 13,[15][16][17] with numerous examples that investigate several facets including the coexistence of four transoid photomerocyanines, 18 photoelectrocyclized structures of spirooxazine derivatives, 19 through to the polyphotochromic behavior of biphotochromic compounds, 20 for example. However NMR studies investigating oligomerically functionalized spirooxazines, wherein the oligomers are essential in allowing "liquid-like" switching speeds when covalently attached to spirooxazines impregnated into solid polymer JOCArticle matrices, and consequential interactions have not been reported.…”

“…The use of NMR to characterize spirooxazines and their photoproducts is well established ,− with numerous examples that investigate several facets including the coexistence of four transoid photomerocyanines, photoelectrocyclized structures of spirooxazine derivatives, through to the polyphotochromic behavior of biphotochromic compounds, for example. However NMR studies investigating oligomerically functionalized spirooxazines, wherein the oligomers are essential in allowing “liquid-like” switching speeds when covalently attached to spirooxazines impregnated into solid polymer matrices, and consequential interactions have not been reported .…”