Diarylethenes for Memories and Switches

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators

Linear and Nonlinear Optical Properties of Photochromic Molecules and Materials.

Reversible Photocontrol of Biological Systems by the Incorporation of Molecular Photoswitches

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Chiroptical Molecular Switches

Organic photochromic systems represent a starting point for the elaboration of light-triggered molecular switching devices. The novel bispyridinium and bispyridine compounds 12+ and 6 were synthesized as their uncyclized isomers from 3,5-dibromo-2-methylthiophene in overall yields of 43 and 44%, respectively. The diarylethene photochromes 2 and 10–13, substituted with electron donors and acceptors, were prepared from 5-methylthiophene-2-carboxaldehyde in 21–32% overall yield. All of the compounds were found to exhibit pronounced photochromic properties. Irradiation with UV light resulted in essentially complete photocyclization of the open forms to the intensely coloured closed isomers which could, in turn, be reconverted back to the open state with visible light of γ>600 nm. The absorption maxima of the described compounds in their closed forms are shifted far towards, and even into, the near-IR region. Whereas no thermochromic properties were observed for the open isomers, the rates of thermal decolouration of the cyclized forms was found to be highly dependent on the nature of the substituents on the thiophene rings. It was demonstrated that reversible photochemical interconversion between the two photochromic states could be used to effectively switch a number of physical properties. Thus, the molecules 12+ and 12 represent two kinds of redox switches, the former in reduction and the latter in oxidation, in which electron conduction is switched on in the closed state and off in the open state. Compound 12 may also be considered to be a photoswitchable analogue of tetrathiafulvalene type substances. On the other hand, compound 2 displays a marked increase in nonlinear optical activity on conversion from the open to the closed form. Such systems are prototypes of photoswitchable molecular wires where electron conduction and push-pull interaction can be reversibly modulated by an external stimulus, namely, irradiation by light.

Light‐Triggered Molecular Devices: Photochemical Switching Of optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species

The bisphenolic dithienylethene molecules 1a and 1b were synthesized in overall yields of 45% from 4-bromoanisole and 44% from 2.6-di-tert-butyl-4-iodophenol, respectively. The corresponding extended quinones 3a and 3b were also prepared. Photochemical studies showed that compounds 1 are photochromic; the open forms 1 could be converted with UV light of 312nm to the closed coloured forms 2 with photostationary states lying at essentially complete conversion (> 98%). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stability for both photoisomers. Cyclic voltammetry studies involving the 2/3 couples showed that whereas 2b undergoes irreversible oxidation at + 0.85 V (vs. SCE in THF), the hydroquinone 2a is reversibly oxidized at an E1/2 of + 0.72V (in MeCN, quasi-reversibly in THF at + 0.81 V); this reflects the differences in deprotonation behaviour of the generated QH2/2+ species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properties. In a complementary fashion, redox switching of the photochromic properties within the 2a-3a pair is possible since 3a is stable to visible light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- and electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the basis for an optical memory system with multiple storage and nondestructive readout capacity through a write-lock-read-unlock-erase cycle.

A Dual‐Mode Molecular Switching Device: Bisphenolic Diarylethenes with Integrated Photochromic and Electrochromic Properties

Solid-state materials containing photochromic dithienylethene derivatives were prepared by the sol-gel process in the form of thin films of a few μm-thick. The effect of substituents (pyridyl or methoxyphenyl) of the optically active molecules on photochromic properties was investigated. Thicknesses and refractive indices either at 633 nm or 785 nm were determined in the colored and in the discolored state by using the Attenuated Total Reflexion method. Sol-gel films containing methoxphenyl substituted molecules show a large refractive index change, Δn=3.10−3 at 785 nm. This variation is important considering the low doping level (0.7 wt%).

Stephen H. Kawai

Papers

Light‐Triggered Molecular Devices: Photochemical Switching Of optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species

A Dual‐Mode Molecular Switching Device: Bisphenolic Diarylethenes with Integrated Photochromic and Electrochromic Properties

Photochromism of Dithienylethene Derivatives Trapped in Sol-Gel Matrices