Photochromism of dihydroindolizines. Part XXIV: Exploiting “Click” chemistry strategy in the synthesis of fluorenyldihydroindolizines with multiaddressable photochromic properties

Abstract A new category of photochromic dihydroindolizines (DHIs) incorporating substituted 2,7- and 4-substituted tetrazole and oxadiazole moieties in the fluorene skeleton (region A) were efficiently prepared utilizing “Click” chemistry approaches. The structure elucidation for all synthesized precursors as well as the target photochromic DHIs was carried out using some analytical and spectroscopic techniques. A highly tunable photochromic behaviors of the parent dihydroindolizine are possible by the introduction of substituents in different positions of the DHI framework. For example, the substituents in 2,7 and 4-positions of fluorene part showed the ability for extending photochromism. The photochromic behaviors of photochromic DHIs substituted in fluorene part (region A) such as the reaction kinetics and fluorescence properties and their photo-fatigue resistance were studied. It has been disclosed that the replacement of the tetrazole moieties in 2,7-position in (region A) by oxadiazole moieties has strong effect on both the spectral, kinetic characteristics, fluorescence emission and photostability. The observations of this work imply that the substituent groups in the fluorene part influenced the thermal back-reaction rates and played an imperative role in controlling all photochromic properties of the open form. The new synthesized substituted (DHIs) in the fluorene by both tetrazole moieties in 2,7-position and by oxadiazole moieties in 2,7 and 4 positions in fluorene part made these materials act as fluorophores and postulate new opportunities for the design of the next generation of photochromic materials which will make it talented materials in many applications such as electronic smart materials, photochromic glasses, photonic devices and fluorescent fabrics. Because of their noticeable fluorescence emission high photostability, these materials can be used as fluorophores, recording or storage information for numerous periods without color fading.