Diarylethenes memory

Such thermally irreversible photochromic chromophores represent the other class, classified as P-type (photochemically reversible type). Although many photochromic compounds have been so far reported, P-type chromophores are very rare. Only two families, furylfulgide derivatives and diarylethene derivatives, exhibit this reactivity.19 101 The photogenerated isomers of these derivatives are thermally stable and never revert to their initial isomers even at elevated temperatures (-100 °C). The thermally stable photochromic compounds offer potential for various applications in photoswitching and memory devices. 

Fig. 11 shows the photoswitching of the injection current. Upon UV irradiation, the hole injection current increased, while decreasing to zero on irradiation with visible light. Very thin amorphous diarylethene film as thin as 0.2 pm could also control the hole injection to the organic hole transport layer (Fig. 9b). These results are potentially applicable to optical memory-type organic photoconductors.

Irie, M. (2000) Diarylethenes for memories and switches. Chemical Reviews, 100, 1685-1716. 

As in previous years, thiophene based diarylethene derivatives constitute an important class of materials which are considered as promising candidates for various kinds of optoelectronic devices, such as switches and optical memories. 

Fukaminato, T., Kobatake, S., Kawai, T, and Irie, M. Three-dimensional erasable optical memory using a photochromic diarylethene single cry stal as the recording medium. Proc. Jpn. Acad. 77, B, 30, 2001. 

The photoreactivity of DTE derivatives in the crystalline state is of special interest because of their potential usefulness for holographic and three-dimensional memories. In crystals, molecules are regularly oriented and packed in fixed conformations. In many cases, free rotation is inhibited. Therefore, the photoreactivity in the crystalline phase is dependent on the space for free rotation of the thienyl rings and the conformation formed in the crystal lattice. Several reports on the synthesis of metal complexes of photochromic diarylethenes and their photo-reactivity in the single-crystalline phase or the photoswitching of the coordination structure have been reported. These studies demonstrate that complexation to metal ions does not prohibit the photochromic reactions of the diarylethene units in the single-crystalline phase. 

T. Tsujioka, N. lefuji, A. Jiapaer, M. Irie, S. Nakamura, Hole-injection isomerization of photochromic diarylethene for organic molecular memory, Appl. Phys. Lett., 89, 222102-222105 (2006). 

Fujimoto Y, Ubukata T, Yokoyama Y (2008) Dendtimer diarylethenes the memory effect of conformation in polymer matrices. Chem Commun 5755-5757. doi 10.1039/b812503a... 

Dithienylethene and derivatives. l,2-Di(2,5-dimethylthien-3-yl)cyclopentene and its derivatives are generally termed dithienylethenes or diarylethenes. Their photochromic properties with the reversible cyclization/cycloreversion are fascinating for chemist and material scientists and have been widely applied to photoswitch, optical memory, etc. in molecular devices and in nanotechnology. Therefore, many researchers are seeking possibilities to move the frontiers. In the last two years many novel dithienylethenes have been prepared and their photochromie properties were investigated. 

Diarylethenes with heterocyclic aryl groups are newcomers to the photochromic field. They belong to the thermally irreversible (P-type) photochromic compounds. The most striking feature of the compounds is their fatigue resistance. The coloration/decoloration cycle can be repeated more than 10 times while retaining the photochromic performance. Both properties, thermal stability of both isomers and fatigue resistance, are indispensable for application to optoelectronic devices, such as devices for memory and switches. In this chapter, recent research on diarylethene derivatives will be described. 

Another example of a metal complex of a diarylethene is shown in Figure 35.9. In this case, the closed ring isomer 21b shows the stronger fluorescence compared to the open-ring isomer 21a. The emission quantum yield of 21b was 0.15 X of excitation 240 nm), while that of 21a was 0.03 (240 nm). Excitation of this compound at 240 nm scarcely affects the photochemical reactivity. Therefore, the system can also be used potentially for nondestructive readout of optical memory. 

---