Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Oxidation and Corrosion of Platinum–Nickel and Platinum–Cobalt Nanoparticles in an Aqueous Acidic Medium

We report on the synthesis, characterization, and corrosion behavior of randomly oriented platinum–nickel and platinum–cobalt nanoparticles (PtNi-NPs, PtCo-NPs). Unsupported and carbon-supported nanocatalysts were synthesized using the “water-in-oil” microemulsion method. X-ray diffraction (XRD) was used to examine their average crystallite size, which was 2.3 nm in both cases. The shape, size, and size distribution of the nanoparticles were evaluated using transmission electron microscopy (TEM); they were determined to be spherelike with an average size of 3.3 and 3.2 nm for PtNi-NPs and PtCo-NPs, respectively, and a narrow size distribution. Comparison of the XRD and TEM data indicated that the nanocatalysts were polycrystalline in nature. Thermogravimetric analysis (TGA) measurements were carried out to evaluate the metal loadings of the carbon-supported nanocatalysts, which were 38.1 wt % for PtNi-NPs and 40.8 wt % for PtCo-NPs. Static Density Functional Theory (DFT) calculations were performed to analyze the structures and energetics of the PtNi and PtCo systems; it was found that the presence of Ni and Co introduced ca. 8% of volume reduction, as compared to the volume of pure, bulk Pt. Cyclic voltammetry (CV) measurements at potential scan rates of 5.0 and 50.0 mV s–1 in 0.50 M aqueous H2SO4 indicated that the specific surface areas (As) of the PtNi-NPs and PtCo-NPs were 74.5 m2 gPt–1 and 33.1 m2 gPt–1, respectively. In situ confocal Raman spectroscopy was successfully used to monitor the formation and reduction of surface oxide layers in the submonolayer and monolayer ranges. Corrosion of the nanocatalysts was studied using anodic and cathodic potentiodynamic polarization (PDP) measurements at a very low potential scan rate of s = 0.10 mV s–1 in 0.50 M aqueous H2SO4 saturated with different gases (N2(g), O2(g), or H2(g)). The nature of the dissolved gas had a profound impact on the corrosion characteristics of the nanoparticles. The nanocatalysts were stable in the electrolyte saturated with H2(g) and underwent slight corrosion in the electrolyte saturated with N2(g) and significant corrosion in the electrolyte saturated with O2(g). The carbon support was also observed to undergo corrosion and porosity changes. The degradation of the nanocatalysts was more pronounced in the case of the anodic PDP measurements than the cathodic ones. Cyclic voltammetry was employed to analyze the loss of As of the nanocatalysts as a result of PDP measurements, and the results were found to corroborate the corrosion data. Evolution of the value of As of the nanocatalysts in 0.50 M aqueous H2SO4 outgassed using N2(g) was examined by recording 500 CV transients in the 0.05 V ≤ E ≤ 1.45 V range at s = 50.0 mV s–1. It was found that in both cases this treatment resulted in a 50% reduction in As

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates