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Photochromic dihydroindolizines (DHIs) 4a,5-dihydropyrrolo[1,2-b]pyridazine based tripodal-linker systems with adamantane core and ethyl benzoate tripods as anchoring groups have been successfully synthesized. In addition, new spirocyclopropene precursors have been prepared through both chemical and photochemical processes. The photochromic properties of the newly synthesized DHIs derivatives have been optimized and fine-tuned by the incorporation of various substituents on the fluorene (region A) and pyridazine (region C) moieties. Several alternative routes for the synthesis of the DHIs under investigation have been established. The Sonogashira crosscoupling reaction was utilized for fragment coupling between DHIs and the phenylacetylene tether of the adamantane core. Several reaction conditions of this key reaction were surveyed to obtain optimal yields of a new series of coupling products targeted for anchoring to semiconductor nanoparticles. The chemical structures of the newly synthesized materials were elucidated by both analytical and spectroscopic tools. Irradiation of the photochromic DHIs with polychromatic light resulted in ring opened colored betaines which underwent cycloreversion reactions via thermal 1,5-electrocyclization processes. The kinetic of the thermal 1,5-electrocyclization was studied by using a UV/VIS/NIR spectrophotometer. The kinetic measurements showed the half-lives of the colored betaines to be in the second domain. A pronounced increase in the half-lives of betaines bearing dimethyl-substituted pyridazine was noted compared with non-substituted pyridazine betaines. A strong effect of solvent polarity on the λ and half-lives of the betaines was observed. The further adjustment of the absorption maxima and the kinetic properties via the manipulation of substituents on the fluorene (region A) and pyridazine moieties (region C) should yield more refined systems for application as supports onto metal-oxide surfaces which remains an active area of our ongoing research. Copyright © 2010 John Wiley & Sons, Ltd. Photochromic DHI-tripodal linker towards anchoring on the metal-oxide nanoparticles have been synthesized. Tuning of the photochromic behavior by structure changes was recorded. [ABSTRACT FROM AUTHOR]

Multi-addressable photophysical properties of new synthesized photochromic materials based on photochromic dihydroindolizine system (DHI) covalently linked to N-acyl-11 aminoundecanoic acid (AUDA) or to its sodium salt or to its ester, through an amidic or urethane linkage have been studied. The DHI skeleton in these compounds is substituted in both the fluorene part (region A) or in the heterocyclic base (region B) with the gelling moieties. These molecules have been designed to respond to their environment. Interestingly, they are shown to act as efficient gelators for polar organic fluids, water and obviously they exhibit a thermosensitive answer as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the DHI subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light, or acidity as external stimuli. These new synthesized photochromic gels with their multi-addressable properties will find their applications as super photoresponsive materials. Developing and tuning of the photophysical properties of the synthesized compounds by the amide and urethane substituents in the 4-position of the fluorene and pyridazine regions have been achieved. The absorption maxima (λmax) and the half-lives (t1/2) of the colored betaines were detected in all cases using UV/VIS spectrophotometric measurements. Irradiation of DHI 12-20 in CH2Cl2 or in acetonitrile solutions at ambient temperature with polychromatic light leads to the formation of red to red-violet colored betaines 12′-20′. The kinetics of the bleaching process of betaines 12′-20′ to DHIs 12-20 were found to take place in the second range (96-218 s) and fit well the first order thermal back reaction. Some of these DHIs showed a photostability higher than that of the standard one. These interesting photophysical properties will help this family of compounds to find useful applications. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this work, photochromic materials based on the dihydroindolizine (DHI) system were synthesized in multistep reactions using chemical and photochemical methods. Some of the synthesized photochromic dihydroindolizine derivatives were substituted on the fluorene (region A) and pyridazine (region C) moieties in order to provide the appropriate functionality for optimal tuning of the photochromic properties of the system. Irradiation of the photochromic DHIs with polychromatic light led to ring opened colored betaines, which underwent thermal 1,5-electrocyclization. The red to green colored betaines produced after UV irradiation returned back through 1,5-electrocyclization to the corresponding DHIs with different rate constants depending on the substituents in both fluorene and pyridazine regions. The kinetic measurements of the thermal 1,5-electrocyclization under different temperatures that ranged from −10 to 25 °C showed that the half-lives of the colored betaines fall in the second to hours domain. Interestingly, these materials showed a very good photochromic behavior not only in solution but also in the PMMA matrix. Irradiation of a slide prepared by the deep-coating method led to the formation of the colored betaine and the kinetics of the thermally reversible 1,5-electrocyclization and the AFM image of the film has been recorded. Indeed, the chemical and thermal stability of the investigated betaines in polymer (PMMA) will render such species useful for a plethora of new of applications. [Copyright &y& Elsevier]