Photon gating

Current research aims at high efficiency PHB materials with both the high speed recording and high recording density that are required for future memory appHcations. To achieve this aim, donor—acceptor electron transfer (DA-ET) as the hole formation reaction is adopted (177). Novel PHB materials have been developed in which spectral holes can be burnt on sub- or nanosecond time scales in some D-A combinations (178). The type of hole formation can be controlled and changed between the one-photon type and the photon-gated two-photon type (179). 

Walter, D. G., Campbell, D. J., and Mirkin, C. A. Photon-gated electron transfer in rwo-component self-assembled monolayers. /. Phys. Chem. B 1999,103, 402-405. 

Recently, two-color, photon-gated PHB was prop< l and observed in some in-(H ganic and organic systems. This proposal was to avoid the hole destruc-... 

Fig. 24. Energy level diagram for BaClFrSm showing the mechanism which allows photon gated holebum-ing to be produced, after Winnakcr et al. (1985).

Winnacker A., Shelby R.M., Macfarlane R.M. Photon-gated hole burning A new mechanism using two-step photoionization. Opt. Lett. 1985 10 350-352... 

Fig. 45 Photon-gated electron transfer in a two component self-assembled mono-layer [223]...

If the inequalities, Eqs. (67) and (69), for the intensities of both burning lasers which take part in the photon-gated HB are fulfilled the angle xjf between dipoles di and da can be found from the following equation [52]... 

Solutions could be found for many of these requirements. For instance, the use of photon-gated hole burning ensures nondestructive read out. Many materials have been discovered in which this concept could be successfully demonstrated however, attempts to unify all the requirements in one system have failed so far. 

In other experiments, the photon-gated transport of Fe(bpy)3 + at conical recessed nanopores, functionalized with a spiropyran (SP) moiety, has been described. Upon exposure to UV light, SP is converted in the presence of a weak acid to the protonated merocyanine, MEH+. MEH+ is converted back to SP by shining visible light on the nanopore orifice. The effect of the photon-generated charges on the diffusion-limited oxidation of Fe(bpy)3 + is significant. In the dark (i.e., with the surface attached molecule in the electrically neutral form, SP), for Fe(bpy)3 oxidation is ca. 8... 

Wang, G. Bohaty, A. K. Zharov, L White, H. S. Photon gated transport at the glass nanopore electrode. JAm Chem Soc 2006,128, 13553-13558. 

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