Photoinduced structural change

Figure 4 Photoinduced structural change of photochromic compounds. (From Ref. 26.)...

Photoresponsive systems are seen ubiquitously in nature, and light is intimately associated with the subsequent life processes. In these systems, a photoantenna to capture a photon is neatly combined with a functional group to mediate some subsequent events. Important is the fact that these events are frequently linked with photoinduced structural changes in the photoantennae. This suggests that chemical substances that exhibit photoinduced structural changes may serve as potential candidates for the photoantennae. To date, such photochemical reactions as E/Z isomerism of azobenzenes, dimerization of anthracenes, spiropyran-merocyanine interconversion, and others have been exploited in practical photoantennae. It may be expected that if one of these photoantennae were adroitly combined with a crown ether, it would then be possible to control many crown ether family physical and chemical functions by means of an ON/OFF photoswitch. This is the basic concept underlying the designing of photoresponsive crown ethers. We believe that this is one of the earliest examples of molecular machines . 

Photoresponsive polymers are quite special polymers, able to respond to light and dark conditions and thus giving rise to reversible variations in their structure and conformation. These photoinduced structural changes may in turn be accompanied by reversible changes in the physical and chemical properties of the polymeric materials. 

Photochromic polymers have been used in order to develop artificial membranes with particular physical properties and functions, such as permeability, conductivity, and membrane potential, that can be switched on and off or otherwise controlled in response to light.17,105,106 More specifically, photochromic polypeptides have been selected as useful materials due to their ability to undergo photoinduced structural change. 

Figure 5.43 (a) Structures of the cis- and frans-thiol-terminated azobenzene-ferrocene dyads, and (b) illustration of the principle of operation of the photogated reaction in the SAM of these complexes, whereby photoinduced structural changes in the monolayer allow solution-phase ferrocyanide ions access to the electrode surface. Reprinted with permission from D. G. Water, D. J. Campbell and C. A. Mirkin, /. Phys. Chem., B, 103, 402 (1999). Copyright (1999) American Chemical Society... 

Murakoshi, K., H. Tanaka, Y. Sawai and Y. Nakato (2002). Photoinduced structural changes of silver nanoparticles on glass substrate in solution under an electric field. Journal of Physical Chemistry B, 106(12), 3041-3045. 

Photoreorientation of azobenzene chromophores by irradiation with polarized light is a very important photoinduced structural change. For azobenzene moieties, there is a widely accepted mechanism for the photo-reorientation The azobenzene moieties that are parallel with their long axis (and therefore with their transition dipole) to the electric field vector... 

Periplasmic space 181 Phase diagram 60-61 Photoinduced structural change 63... 

Puchenkov and Malkin [107] and Chen and Diebold [108] presented theoretical treatments on the temporal profile of the acoustic wave induced by volume expansion. Both theories showed that the temporal profile of the thermally induced acoustic wave and the volume induced wave are different. The thermodynamic treatment told us that the TG signal by photoinduced structural change appears as the fast rise, which is determined only by the pulse width (if the chemical reaction proceeds very fast). This finding is consistent with the observations by Miller and co-workers [12,25,106]. If the volume expansion takes place after excitation, and is subsequently followed by contraction by the deactivation, the pressure wave induced by the volume change should be different from that expected by the thermal expansion [108]. Indeed, this expected different pressure wave was observed in the TG signal after the photoexcitation of emulsions [109a] and carbon particles [109b]. The pressure wave was explained by the thermal expansion... 

Fig. 3.12 Photoinduced structural changes in [Pt2(P205H2)4]" in solution obtained from EXAFS studies. Transient data (circles) and best fit (solid line) were obtained with the following parameters a Pt-Pt contraction of 0.31(5) A, a Pt-ligand elongation of 0.010(6) A, zero energy shift, and 7 % excitation yield. The error bars represent the standard error of the measurement. Red circles oxygen, orange circles P, grey circles Pt, small white circles H atoms. Adapted with permission from Ref. [59]. Copyright 2009, John Wiley Sons...

Zhou W., Paesler M., and Sayers D. E., Structure and photoinduced structural changes in nonstoichiometric As Sj. A study by x-ray-absorption fine-structure study, Phys. Rev. B, 46, 3817-3821 (1992). 

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