Photochromism of dihydroindolizines. Part XVIII: palladium-catalyzed Negishi coupling for the synthesis of photochromic dihydro 5-azaindolizine-linker-conjugates with a terminal ethylene anchoring group

Eight new photochromic dihydro 5-azaindolizine-linker-conjugates with a terminal ethylene anchoring group have been synthesized via palladium-catalyzed Negishi coupling. Polychromatic light irradiation of the photochromic dihydro 5-azaindolizines (DHAIs) led to ring-opened colored betaines which underwent reversible thermal 1,5-electrocyclization into their corresponding DHAIs in the second domain. The noteworthy multiaddressable photochromic properties are useful for a plethora of new applications for these materials such as anchoring the ethylene group to metal-oxide nanoparticles.     

Photochromism of Dihydroindolizines. Part III [1]. Synthesis and Photochromic Behavior of Novel Photochromic Dihydroindolizines Incorporating a Cholesteryl Moiety

Summary. Ten novel photochromic dihydroindolizines (DHIs) based on 1,5-electrocyclization and bearing a cholesteryl moiety at 7-position of the DHI skeleton were synthesized. 1D, 2D, NOESY ¹H NMR spectra, mass spectrometry, and elemental analysis were used for their characterization. Irradiation of the DHIs in CH₂Cl₂ solution with polychromatic light leads to the formation of red to red-violet colored betaines. Most colored betaine forms are notable in CH₂Cl₂ solution at room temperature because of their slow 1,5-electrocyclization except in one case, where the colored betaine could be observed only after cooling with liquid nitrogen due to the fast electrocyclization back reaction. The kinetics of the reverse 1,5-electrocyclization of the colored betaines into the corresponding DHIs were detected using both UV/VIS and flash photolysis measurements.The presence of three isosbestic points in the fading spectrum of the betaines proved that the thermal back reaction to the DHIs follows a first order mechanism. Tuning of the photophysical properties of DHIs and their colored betaines was achieved by change of substituents in the ester and fluorene regions. A notable increase of the t₃₀-value of some betaines by a factor ranging between 1.01 and 1.57 compared with the betaine form of dicyanopridazine DHI standard (t₃₀=243min) was observed. The high photo-fatigue resistance of these betaines will help to find their applications.Present address: Special Division for Human Life Technology, National Research Institute of Advanced Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan     

α-Decay near the shell closure from ground and isomeric states

The modified two-potential approach (MTPA) is employed to study the exotic α-decay near the closed shells Z=82 and N=82, 126 within a deformed version of the cluster model. We perform systematic calculations on favored α-decay half-lives from both the ground states (g.s.) and the isomeric states (i.s.) by using the microscopic double-folding potential. The obtained α-decay half-lives are found to be in good agreement with the experimental data. This indicates that four types of α transitions among ground states and isomeric states (g.s. → g.s., g.s. → i.s., i.s. → g.s., i.s. → i.s.) are well described in a unified model. In addition, the unfavored α transitions in the Bi isotopes are investigated to pursue a further understanding of α-decay properties.     

New approach for alpha decay half-lives of superheavy nuclei and applicability of WKB approximation

The α decay half-lives of recently synthesized superheavy nuclei (SHN) are calculated by applying a new approach which estimates them with the help of their neighbors based on some simple formulas. The estimated half-life values are in very good agreement with the experimental ones, indicating the reliability of the experimental observations and measurements to a large extent as well as the predictive power of our approach. The second part of this work is to test the applicability of the Wentzel-Kramers-Brillouin (WKB) approximation for the quantum mechanical tunneling probability. We calculated the accurate barrier penetrability for alpha decay along with proton and cluster radioactivity by numerically solving Schrödinger equation. The calculated results are compared with those of the WKB method to find that WKB approximation works well for the three physically analogical decay modes.     

Photochromism of dihydroindolizines. Part 16: Tuning of the photophysical behavior of photochromic dihydroindolizines in solution and in polymeric thin film

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.     

α-Decay calculations of medium mass nuclei within generalized density-dependent cluster model

The α-decay half-lives of even–even medium mass nuclei have been systematically investigated using a radial wave function within the generalized density-dependent cluster model. The α-decay width is calculated using the overlap integral of the quasi-bound initial state wave function, the scattering final state wave function, and the difference of potentials. The effective α–nucleus potential is constructed using the double-folded integral of realistic nucleon–nucleon interactions with the mass density distributions of α particles and daughter nuclei. For comparison calculations are also carried out for the Woods–Saxon shape potential. The present study is restricted to even–even nuclei with 82<N126, where the shell effect on the α-preformation factor has been taken into account for even–even N=126 isotones. The obtained α-decay half-lives are found to agree with the experimental data with a mean factor of less than 2 for both the double-folded potential and the Woods–Saxon shape potential.