Photoinduced intramolecular

Williams R M, Zwier J M and Verhoeven J W 1995 Photoinduced intramolecular electron transfer in a bridged Cgg (acceptor)-aniline (donor) system. Photophysical properties of the first active fullerene diad J. Am. Chem. See. 117 4093-9... 

Yonemura, H., Noda, M., Hayashi, K, Tokudome, H., Moribe, S. andYamada, S. (2002) Photoinduced intramolecular electron transfer reactions in fiillerene-phenothiazine linked compounds effects of magnetic field and spacer chain length. Mol. Phys., 100, 1395-1403. 

Ikegami M, Arai T (2002) Photoinduced intramolecular hydrogen atom transfer in 2-(2-hydroxyphenyl)benzoxazole and 2-(2-hydroxyphenyl)-benzothiazole studied by laser flash photolysis. J Chem Soc Perkin Trans 2 1296-1301... 

E. Galoppini, M. A. Fox, Effect of the Electric Field Generated by the Helix Dipole on Photoinduced Intramolecular Electron Transfer in Dichromophoric Alpha-Hdical Peptides , J. Am. Chem. Soc 1996, 118, 2299-2300. 

Delmond S, Letard JF, Lapouyade R et al (1996) Cation-triggered photoinduced intramolecular charge transfer and fluorescence red-shift in fluorescence probes. New J Chem 20 861-869... 

Compounds undergoing photoinduced intramolecular charge transfer (ICT) and internal rotation... 

Photoinduced intramolecular interaction of t-S and tertiary amine moieties linked with a polymethylene chain has also been studied24. The photoexcitation of fraws-stilbene in which a tertiary amine is attached to the ortho position with a (CH2)i-3 linker leads to fluorescent exciplexes by intramolecular electron transfer, and results in no more than trans-cis isomerization. The failure to give adducts from the intramolecular exciplexes could arise from the unfavourable exciplex geometry to undergo the necessary bond formation. 

Similar experimental studies were carried out on molecules in which the bridge is constituted by conjugated groups [83, 84]. General references on photoinduced intramolecular electron transfers may also be found in two recent reviews [85, 86]. 

Photoinduced intramolecular electron transfer in the donor-acceptor complex 87 (R = H) generates transient charge-separated open-shell species with the remarkably long lifetime of about 75 ps [89]. Dyads that contain Tt-extended tetrathiafulvalene units also form stable cationic species upon oxidation [90]. The dumbbell shaped triad 91 [91-93] (Scheme 4.13) was obtained by carrying out the reaction with the in situ generated bis-diene at room temperature, in the dark and in o-dichlorobenzene as a solvent in 50% yield. The product is thermally unstable and easily undergoes a retro-Diels-Alder reaction [91]. 

Investigation of photoinduced intramolecular ET processes in such systems has in general shown that, compared to analogous porphyrin/quinone systems, i. charge separation occurs with higher efficiency and ii. charge-separated states have longer lifetimes (Scheme 9.4). Such a behavior is the result of the combination of two... 

Fig. 3. Time-resolved stimulated emission signal of 10-hydroxybenzoquinoline (10-HBQ) in cyclohexane (30 mM) with excitation at 360 nm and probe at 620 nm. Photoinduced intramolecular proton transfer reaction of 10-HBQ is also shown in the inset.

Studies of fluorescence quenching in 8-bond pairs in solvents such as diethylether and acetonitrile, allowed a rate of the photoinduced intramolecular electron transfer of the order of 109s 1 to be estimated, showing that very rapid intramolecular transfer can also occur in the excited bifunctional molecule. 

Wagner and McMahon [101] have irradiated compounds bearing chiral auxiliaries and observed that high diastereoselectivity can be achieved with photoinduced intramolecular ortho cycloaddition (Scheme 26). Carbon atom 8 is the only permanent new stereocenter created by the ortho photocycloaddition. WhenX = (2R,5R)-( )-2,5-dimethylpyrrolidine or(7/ )-H Fcamphorsultam, di-astereomeric excesses as high as 90% are obtained. The (85)-cyclooctatriene-sul-tam derivative could be isolated as a single diastereomer after one recrystallization. 

We have reported further improvements in the photorefractive sensitivity of liquid crystals by doping with chromophores that undergo efficient photoinduced intramolecular charge transfer [24], The magnitude of the observed photorefrac-... 

Photoinduced Intramolecular Electron Transfer Within Porphyrinic Rotaxanes... 

Photoinduced intramolecular electron tunneling was observed also in some other porphyrin containing bridge molecules, such as porphyrin covalently linked to phenolphthalein [308], dimethylaniline — mesoporphyrin II — quinone triad [309], Zn porphyrin-viologen-quinone triad [310], carotenoid — porphyrin -diquinone tetrad [311]. The influence of conformational state of porphyrin-viologen bridge molecules on the rate of PET reactions was studied in Ref. [312]. 

Oxepinotropones like 147b, in contrast to 1-benzoxepines, do not undergo photoinduced intramolecular cyclization [94H(38)957],... 

In preparing the highly neuroexcitatory o-anisyl derivative 26, Shira-hama and co-workers utilized a photoinduced intramolecular Diels-Al-der reaction of precursor 32, itself derived from optically active vinyl glycinol (Scheme 8).32 Although an attractive and relatively short synthetic route, the possibilities for modification of the C-4 aryl substituent were felt too limited for our purposes. 

Loway et al. have prepared an aziridine by the application of photoinduced intramolecular aziridination the aziridine was subsequently converted to L-daunosamine glycoside (Scheme 4.65) [98]. 

A detailed discussion of the energetics of photoinduced intramolecular ET in organic dyads is available in the literature [44]. Therefore, only a brief discussion of the energetic features which are unique to transition metal dyads are presented herein. The free energy for photoinduced forward and back ET (AG and AGbet, respectively) between an electron donor and an electron acceptor (D and A, respectively) is given by... 

VI. PHOTOINDUCED INTRAMOLECULAR ELECTRON TRANSFER IN METAL-ORGANIC DYADS ... 

Based on their easily tunable photophysical and redox properties, transition metal complexes are versatile components to be used in the construction of photochemical molecular devices. The studies presented in this article show that the combination of the Ru(bpy)22+ photosensitizer and cyanide bridging units allows the synthesis of a variety of polynuclear systems that exhibit interesting photochemical properties. Depending on the nature of the attached metal-containing units, supramolecular systems can be obtained that undergo efficient photoinduced intramolecular energy or electron transfer processes. 

Wasielewski, M.R., Niemczyk, M.P. and Svec, W.A., 1982. Selectively metalated doubly cofacial porphyrin trimers. New models for the study of photoinduced intramolecular electron transfer, Tetrahedron Lett.. 3215-3218. 

A much more deep-seated photorearrangement than in the dibenzo[2.2.2] systems occurs in the dibenzo[3.2.1] compound 55 with chloride or bromine as nucleofugal group at C-8 (equation 49)229. 9-Functionalized phenanthrenes are formed, supposedly also by way of photoinduced intramolecular electron transfer in the (triplet) excited state. 

Benzoindole 114 has been synthesized by a remarkable sequence, in which the benzannulation precursor 113 is pre-assembled starting from two different chromium carbenes. It is formed in a [3+2] cycloaddition, in which the acylamino carbene complex 111 acts as the dipolar component and the alkynylcarbene complex 112 serves as the dipolarophile. The resulting 3-pyrrolylcarbene complex 113 undergoes a photoinduced intramolecular benzannu-lation to give the benzoindole 114 [84a]. This strategy complements an approach towards carbazoles [84b], Isoindolines and 1,2,3,4-tetrahydroisoquinolines are accessible from the reaction of pentacarbonyl (a-methoxyethylidene) chromium with 7r,co-dialkynes bearing a nitrogen atom in the carbon ether [84c]. 

Takashima H,Tara C, Namikawa S, Kato T, Araki Y, Ito O, Tsukahara K. Photoinduced intramolecular electron-transfer reactions of reconstituted met- and zinc-myoglobins appending acridine and methylacridinium ion as DNA-binders. J Phys Chem B 2006 110 26413-23. 

The intramolecular ET rate constants are 1600 s (low- to high-potential heme) and 40 s l (high- to low-potential heme). As expected from the accompanying spin change (cf. above) and the small driving force, these values are low compared with many data for strongly exothermic photoinduced intramolecular ET processes in metalloprot-eins [5, 19, 20]. 

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