Photo-switchable

Bates, M., Huang, B., Dempsey, G. T. and Zhuang, X. (2007). Multicolor super-resolution imaging with photo-switchable fluorescent probes. Science 317, 1749-53. 

The use of T2D-IR spectroscopy in its various modes is not limited to MLCT. It is applicable to all kinds of photo-triggered processes. Besides the investigation of electronically excited states, photo-chemical reactions like isomerizations and dissociations can be explored. Application to a photo-switchable peptide has already been demonstrated [10]. Conformational dynamics of biomolecules that are triggered by laser-induced T-jump or the control of pH by photo-acids, can also be investigated. 

Fig. 6.15 Different forms of inclusion of eo-sin guest molecules in (isomeric) photo-switchable POPAM host compounds. The number and position of the included eosin molecules vary according to the conditions...

Hamada, F. Fukushima, M. Osa, T. Ikeda, H. Toda, F. and Ueno, A. (1993) Azobenzene-capped y-cyclodextrin as photo-switchable host, Makromol. Chem., Rapid Commun. 14, 287-291. 

Scheme 7 Electronic transduction of photo-switchable bioelectrocatalytic functions of proteins, (A) by the tethering of photoisomerizable units to the protein (R is a diffusional electron mediator that electrically contacts the redox...

GOx (22a). (b) protonated nitromerocyanine-tethered GOx, (22b). I nset Reversible photo-switchable amperometric transduction of the bioelectrocatalyzed oxidation of glucose by 22a - ( ) and 22b-(o). 

Very recently, the azobenzene norbornene derivative XI (Scheme 2) was successfully prepared and polymerized with initiator 5 and 9, and it showed a nematic mesophase. The polymer was photo-switchable due to photo cisltrans-isomerization of the N=N double bond [65]. This is the first step towards ROMP-derived materials that may be used for optical data storage. 

Fig. 20.2. Photo-switchable probes constructed from activator-reporter pairs, (a) Spectrally distinct reporters exhibit photo-switching behavior. The lower panel shows the fluorescence time traces of Cy5, Cy5.5, and Cy7 when paired with a Cy3 dye as the activator. The upper panel shows the green laser pulses used to activate the reporters. The red laser was continuously on, serving to excite fluorescence from the reporters and to switch them off to the dark state, (b) The same reporter can be activated by spectrally distinct activators. The lower panel shows the fluorescence time traces of Cy5 paired with different activators, Alexa Fluor 405 (A405), Cy2, and Cy3. The upper panel shows the violet (405nm, magenta line), blue (457nm, blue line), and green (532 nm, green line) activation pulses...

In addition to the photo-switchable cyanine dyes, other photo-activatable dyes such as caged fluorescent compounds [5] and photo-chromic rhod-amine [22], as well as photo-switchable fluorescent proteins, such as PA-GFP [23], Kaede [24] and EosFP [25], KikGR [26], Dronpa [27,28] and rsFastLime [29], and photo-switchable CFP2 [30] can also be used for STORM/PALM/ FPALM imaging. 

In addition to using the photo-switchable cyanine dyes, multi-color superresolution imaging can also be accomplished by using photo-switchable fluorescent proteins [34] or a combination of dyes and fluorescent proteins [35]. 

Fig. 8A-C. Molecular switches based on the binding ability of crown ethers. A A photo-switchable binding event based on conformational change upon azobenzene isomerization. B A photoswitchable binding event based on both conformational and electrostatic changes. C A redox-switchable calix[4]arene-crown ether...

Linkage isomerizations have also been observed for other small molecules such as N2, N02, NCS, S02, and dimethylsulfoxide (DMSO).15 The isomers are likely participants as intermediates in biorelevant ligand interchange or addition processes, in the NO recombination after photolysis, or even in the route to NO release from the ES in aqueous, room-temperature photochemistry (Section 7.7). Indeed, the photo-switchable nitrosyl compounds are an attractive class of materials with favorable photochromic and photorefractive properties, potentially useful for optical and biomedical applications. 

FIG. 7.4 (A) Use of diffusional electron relay to amplify the electrochemical stpial of the photo-switchable phenoxynaphthacene quinone/tetradecanethiol mixed monolayer. (B) Cyclic voltammograms of the electrode in the presence of BV (2) (I mM) (a) in the trans-quinone state (la) and (b) In the ono-quinone state (I b), Recorded at pH 7.5, scan rate 5 mV s. Inset Photoswitching behavior of the electrocatalytic current (Adapted from reference 43, Figure 8, scheme 5. Copyright 1996, American Chemical Society.)... 

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