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

Abstract

AbstractTwenty‐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 1a–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 betaines­3a–χ were also observed. Copyright © 2002 John Wiley & Sons, Ltd.