1 research outputs found
Synthesis and Photoswitching Studies of OPE-Embedded Difurylperfluorocyclopentenes
We report the synthesis and photochemical
behavior of five photochromic
molecular switches <b>7a</b>–<b>e</b> with attached
molecular wires based on differently substituted oligoÂ(phenylene ethynylene)
(OPE) building blocks. The switchable molecular wires <b>7a</b>–<b>e</b> were built in a convergent approach from substituted
iodotolans <b>6a</b>–<b>e</b> and 1,2-bisÂ(2-methyl-5-ethynylfuran-3-yl)Âperfluorocyclopentene <b>5</b> by 2-fold Sonogashira coupling. Compound <b>5</b> was
prepared from the corresponding bis-aldehyde <b>2</b> by Wittig-type
olefination with [PPh<sub>3</sub>CHBr<sub>2</sub>]ÂBr·CH<sub>3</sub>CN, followed by elimination to the bromoalkyne under mild phase-transfer
conditions at 0 °C. Halogen–metal exchange with <i>i</i>-PrMgCl·LiCl and hydrolysis furnished <b>5</b> in good overall yield. Substituents R<sup>1</sup> and R<sup>2</sup> in the OPE portion were either electron-withdrawing or electron-donating,
and their influence on the photostability and photoswitching characteristics
of <b>7a</b>–<b>e</b> was studied. All resulting
molecules show reversible photochromism between the colorless off
and the deeply colored on states when irradiated with light of 313
and 576 nm wavelengths, respectively. The quantum yields of these
photoreactions increased when electron-withdrawing groups were used.
This was further corroborated by reversible protonation/deprotonation
of <b>7e</b> (R<sup>1</sup> = NMe<sub>2</sub>, R<sup>2</sup> = H) for which the ring-closing quantum yield increased 10-fold
upon switching off the donor by protonation