Evidence for a photophysical deactivation pathway competing with the photochromic transformation in a cyano-substituted spironaphthoxazine

Ultrafast Spintronics: Dynamics of the Photoisomerization-Induced Spin-Charge Excited-State (PISCES) Mechanism in Spirooxazine-Based Photomagnetic Materials

The optical control of spin state is of interest in the development of spintronic materials for data processing and storage technologies. Photomagnetic effects at the single-molecule level have recently been observed in the thin film state at 300 K in photochromic cobalt dioxolenes. Visible light excitation leads to ring-closure of a photochromic spirooxazine bound to a cobalt dioxolene, which leads to generation of a high magnetization state. Formation of the photomagnetic state occurs through a photoisomerization-induced spin-charge excited-state process and is dictated by the spirooxazine ligand dynamics. Here, we report a mechanistic investigation by ultrafast spectroscopy in the UV-vis region of the photochemical ring-closing process in the parent spirooxazine, azahomoadamantylphenanthroline spirooxazine, and the photomagnetic spirooxazine cobalt-dioxolene complex. The cobalt appears to stabilize a photomerocycanine transient intermediate, presumably the TCC isomer, formed along the ground-state potential energy surface (PES). Structural changes associated with the TCC isomer induces formation of the high-spin Co(II) form, suggesting that magnetization dymanics can occur along the excited-state PES, leading to ultrafast switching on the ps time scale. We demonstrate the full ring closure of the spiro-oxazine ligand is not required to switch magnetization states which can be induced with a higher yielding isomerization reaction. The ability of this system to undergo optically induced spin state switching on the ps time scale in the solid state makes it a promising canididate for resistive nonvolatile memory technologies.

Joint spectroscopic and theoretical investigation of cationic cyanine dye Astrazon Orange-R: solvent viscosity controlled relaxation of excited states

In this paper, the first study of cationic cyanine dye Astrazon Orange-R by combined spectroscopic and theoretical investigation is presented.

Gas-Phase Dynamics of Spiropyran and Spirooxazine Molecules

The gas-phase dynamics of two classes of photochromic molecules, three spiropyrans and one spirooxazine, have been investigated here using both time-resolved mass spectrometry and photoelectron spectroscopy approaches. It is, to our knowledge, the first gas-phase experiment done of these kinds of molecules. The molecules are excited at 266 nm and probed at 800 nm. The comparison of the dynamics of these four molecules has been used to propose a sequential photoisomerization mechanism involving four steps occurring in the first 100 ps. Each of these steps is discussed and related to the observed condensed-phase dynamics and to theoretical calculations.