Photochromism of dihydroindolizines. Part XX: Synthesis and photophysical behavior of fluorenyldihydroindolizines photochromes based “Click” chemistry strategy

•For the first time, “Click chemistry” methodology for the synthesis of photochromic dihydroindolizines has been successfully applied.•Optimization of the three alternative synthetic pathways of the target photochromic DHIs has been designed.•Characterizations of the synthesized photochromic DHIs where established on the basis of spectroscopic and analytical tools.•Broad spectrum photochromic properties have been recorded.

Novel type of photochromic dihydroindolizines (DHIs) bearing substituted 2,7- disubstituted triazolofluorene (region A) with different acetylenic linker-conjugates and substituted pyridazines as heterocyclic base (region B) have been productively synthesized through “Click” chemistry strategies by different chemical and photochemical pathways. The chemical structures of the new photochromic triazolo-dihydroindolizines were established on the bases of analytical and spectroscopic tools. Polychromatic light irradiation of the photochromic DHIs led to ring opened colored betaines, which underwent reversible thermal 1,5-electrocyclization. The red to reddish-violet betaines returned back through 1,5-electrocyclization to the corresponding DHIs with diverse rate constants depending on the subsitutents in fluorene terminal triazole moieties. The unique photochromic properties of newly synthesized compounds maybe useful for a plethora of new applications.

Graphical abstractRepresentation of the optimized (MM2) structure of photochromic DHI 10a based “Click” chemistry strategy.Figure optionsDownload full-size imageDownload as PowerPoint slide