Photochromism of dihydroindolizines. Part II - Synthesis and photophysical properties of new photochromic IR-sensitive photoswitchable substituted fluorene-9′-styrylquinolinedihydroindolizines

Abstract

Twenty-nine new photochromic 2,4,7-substituted fluorene-9′-styrylquinolinedihydroindolizines (DHIs) 4a-χ were prepared in 45-75% yield via nucleophilic addition of 4-styrylquinolines 2a-k to substituted spirocyclopropenes la-c. The absorption maxima (λmax) of the colored betaines 3a-χ were detected by flash photolysis measurements. All betaines 3a-χ showed two absorption maxima, one in the visible region (450-525 nm) and another in the IR region (825-950 nm). Absorption spectra of betaines 3a-χ were also recorded at low temperature (77 K) by FT-UV-Vis-near-IR spectroscopy. The kinetics of the fast cyclizing process of betaines 3a-χ to DHIs 4a-χ were studied by millisecond flash photolysis and were found to take place in the millisecond range (35-310 ms in dichloromethane solution and 50-425 ms in methanol solution). A transient lifetime (ca 1 ms), measured using laser flash photolysis, was attributed to the transformation of (Z) to (E)-betaines 3. Large solvatochromic effects on the absorption maxima (λmax) and a substantial increase in the half-lives (t1/2) with solvent polarity of betaines 3a-χ were also observed. Copyright © 2002 John Wiley & Sons, Ltd.