Single photochromic

Figure 13 Response of a singly photochromic system to light irradiation commences at time and ends at t2...

Holland NB, et al. 2003. Single molecule force spectroscopy of azobenzene pol5uners switching elasticity of single photochromic macromolecules. Macromolecules 36(6) 2015 2023. 

Holland, N., Huge , T., Neuert, G., Cattani-Scholz, A., Renner, C., Oesterhelt, D., Moroder, L, Seitz, M., and Gaub, H. (2003) Single molecule force spectroscopy of azobenzene polymers switching elasticity of single photochromic macromolecules. Macromolecules, 36(6), 2015-2023. 

QDs excited by single or multiple photons exhibit multixponen-tial decays, in our hands generally with two components of <10 and 10-25 ns. This property renders the nanoparticles useful reagents for the systematic modulation of emission via a technique we have denoted as photochromic FRET (pcFRET, Fig. 12.5 see [1, 2, 134]). The method was developed in order to circumvent inherent limitations in the quantitative determination of FRET in cells, particularly in imaging applications. We have classified pcFRET as a member of the family of so-called acceptor depletion methods [1, 2] due to the reversible change in the structure, and thus spectroscopic properties, of the photochromic compound (e.g., a diheteroarylethene) serving as the FRET acceptor. The key... 

He J, Chen F, Liddell PA, Andreasson J, Straight SD, Gust D, Moore TA, Moore AL, Li J, Sankey OF, Lindsay SM (2005) Switching of a photochromic molecule on gold electrodes single-molecule measurements. Nanotechnology 16(6) 695... 

Naumov P, Yu P, Sakurai K (2008) Electronic tera-order stabilization of photoinduced metastable species structure of the photochromic product of spiropyran determined with in situ single crystal X-ray photodiffraction. J Phys Chem A 112 5810-5814... 

All the 311 molecules adopt a P-helical conformation in the central hexatriene part (this crystal is named (P)-311 NpF). Single crystals with the opposite chirality, (M)-311 NpF, in which 311 is in an M-helical conformation, were also obtained from the same sample batch. The chiral cocrystals underwent photochromism. Upon irradiation with 365 nm light, the colorless crystal turned blue. 

The absorption spectrum at 0° has a maximum at 600 nm. Upon rotation of the direction of the incident polarized light by as much as 90°, the absorption intensity decreases. The anisotropy of the absorption spectra reflects the regular orientation of the photogenerated closed-ring isomers and indicates that the photochromic reaction occurred in the single-crystalline phase. The blue color disappeared by irradiation with visible light a > 480 nm). Anthracene-substituted derivatives also showed photochromic properties (01JPC(A)1741). 

Photochromism has also been observed when two porphyrinic groups are linked to a dithienylethene scaffold. The closed form showed an absorption band at 560 nm (01JA1784). The same behavior was observed in the system 318-319 (02AM918). Dithienylethene photochromic systems have also been described to be linked to single-walled nanotubes (07JA12590). 

Photochromism is a reversible transformation of a single chemical species between two states, the absorption spectra of which are clearly different, the transition in at least one direction being induced by electromagnetic radiation [1], The widest and most important group of the photochromic system is based on electrocyclic reactions [2,3] a few have been commercially successful (polymer-based photochromic eyewear, novelty items and security printing inks). Several other photochromic systems based on E,Z-isomerization, cycloaddition reaction, electron or proton transfer have potential industrial applications [4],... 

Yamamoto, S., Matsuda, K., and Irie, M. (2003) Absolute asymmetric photocyclization of a photochromic diarylethene derivative in single crystals, Angew. Chem. Int. Ed., 42, 1636-1639. 

There are different types of photochromic systems (5), e.g. triplet-triplet absorption, cis-trans isomerization or homolytic dissociation reactions. Since lignin has a very heterogenous and complex structure there is probably not a single responsible system, but rather a mixture of systems. 

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