Effect of thermal cycling on the martensitic transformation in two kinds of Cu-Zn-Al shape memory alloys, whose parent phases are ordered into D03 and B2 types, has been examined by electrical resistivity vs. temperature measurement, optical and transmission electron microscopy and X-ray diffraction. The thermal cycling was carried out between 77 K below Mf temperature and 288 K above Af temperature up to 104 times. With increasing thermal cycle, Ms temperature of the B2 type alloy (Cu-29.1Zn-6.7Al (at.%)) increases, while that of the D03 type alloy (Cu-12.5Zn-19.4Al (at.%)) decreases. The change in Ms temperature is about 10 and 15 K in the B2 and D03 type alloys, respectively, after 103 reproducible after 10 cycles or so, and in addition, residual martensites at room temperature become noticeable roughly after 102 cylces, as reported previously. On the other hand, the martensitic structure creasing thermal cycle, and the microstructural reproducibility is poor even after 103 cycles, as in a CuAl-Ni alloy previously studied. Numerous dislocations are accumulated in the parent phases of both the thermal cycled alloys. The density of the dislocations appears to be higher in the B2 alloy than in the D03 alloy. Disordering takes place in the parent phases of both the alloys with thermal cycling, as in the CuAl-Ni alloy. The observed change in Ms temperature in each alloy is considered to be caused by the disordering. Characteristics of the disordering suggest that dislocations with the Burgers vector of 1/4•<111) and 1/2•<111> are generated in the D03 and B2 parent lattices, respectively, by thermal cycling. The feature of disordering is different from that in the Cu-Al-Ni alloy previously examined, and is inconsistent with the result of a previous analysis made on B2 type Cu-Zn-Al alloys. Mechanisms of the disordering by thermal cycling in both the alloys are discussed.
Development of organic fluorophore is an important theme. Especially, the fluorophores with longer fluorescence peaks are useful to biological probes. One of the methods to change the fluorescence peak is the introduction of substituents. However, opposing characteristics of the substituents lead to different changes in the fluorescence peaks. Furthermore, the introduction of the substituent also affects their electric properties. Thus, if the materials were developed with the substituent effect on the optical and electric properties separately, it will be useful to design the functional materials related to both optical and electric properties. Herein, we investigated the substituent effect of dipyrrolo[1,2-a:2′,1′-c]quinoxalines on fluorescence properties. We synthesized the compounds bearing electron-donating or electron-withdrawing substituents at the benzene ring on dipyrrolo[1,2-a:2′,1′-c]quinoxaline, which would have more direct influence on the optical properties. By introducing each substituent at the 6 position of dipyrrolo[1,2-a:2′,1′-c]quinoxaline, the bathochromic shift was observed in the fluorescence spectra. In the case of fluorine substituent, the change of the fluorescence peak reached was about 19 nm. Using a TDDFT calculation, we explained the reason for such a substituent effect that large on the increment of LUMO energy or decrement of HOMO energy occurred by introducing electron-withdrawing or electron-donating substituents at the 6 position, respectively. The substituent effect on the change of orbital energies is typical although the different characteristics of substituents resulted in the similar tendency about the change of fluorescence peak. Furthermore, with the introduction of phenyl substituents at the 3 and 10 positions, we achieved 40–50 nm longer fluorescence peaks compared with that of the original dipyrrolo[1,2-a:2′,1′-c]quinoxaline.
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