Proton exchange and isomerisation reactions of photochromic and reverse photochromic spiro-pyrans and their merocyanine forms
- 1 January 1999
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Physical Chemistry Chemical Physics
- Vol. 1 (14) , 3259-3267
- https://doi.org/10.1039/a902379h
Abstract
Photochromic 1′,3′,3′-trimethyl-6,8-dinitro-spiro- [2H-1-benzopyran-2,2-indoline], (6,8-dinitro BIPS) has been studied in different solvents using 1H-NMR techniques, UV/visible spectroscopy, X-ray diffraction and electrospray ionisation mass spectroscopy (ESI-MS). Molar decadic absorption coefficients for 6,8-dinitro BIPS were found to range between 35000–45000 d mol-1 cm-1. 1H–1H NOESY and 1H-NMR experiments have established that in solution the merocyanine form of 6,8-dinitro BIPS is in rapid exchange between the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers. The 3B proton on the central bridging double bond of spiro-pyran merocyanines is labile in organic solvents. The closed form of 6,8-dinitro BIPS enantiomerises about the spiro C(2) carbon at a rate of 18 s-1 at 300 K. The activation energy for this process was estimated to be 46 kJ mol-1 using dynamic NMR.Keywords
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