Cyanines during the 1990s: A Review

Cy5 is one of a few commercially available dyes in the near-infrared wavelength range. In this study, the fluorescence fluctuations of Cy5 have been investigated under steady-state excitation conditions by fluorescence correlation spectroscopy (FCS). The fluctuations in fluorescence are compatible with and can be used to characterize the photoinduced isomerization and back-isomerization, as well as the transitions between the singlet and triplet states of the dye. By employing a simple kinetic model, the rate constants of these processes can be determined. The model was used over a broad range of experimental conditions, where the influence on the isomerization properties of solvent viscosity, polarity, and temperature, excitation intensity and wavelength, and the presence of different side groups was investigated. We propose FCS as a useful and simple complementary approach to study isomerization processes of cyanine dyes yielding information about the rates of both the photoinduced isomerization and the...

Characterization of Photoinduced Isomerization and Back-Isomerization of the Cyanine Dye Cy5 by Fluorescence Correlation Spectroscopy

Compounds of the formula (I), wherein R1, R2 and R10 independently of one another are C1-C20alkyl, phenyl, C1-C12alkylphenyl or phenyl-C1-C6alkyl; R3 and R4 independently of one another are hydrogen, C1-C20alkyl, NR6R7 or SR8, provided that at least one of R3 or R4 is NR6R7 or SR8; R5 is hydrogen or C1-C20alkyl; R6 and R7 independently of one another are C1-C20alkyl, or R6 and R7 together with the N-atom to which they are attached form a 5 or 6 membered ring, which optionally is interrupted by O, S or NR9 and which optionally additionally is substituted by one or more C1-C4alkyl; R8 is phenyl, biphenylyl, naphthyl, anthryl or phenanthryl, all of which optionally are substituted by one or more C1-C4alkyl; and R9 is hydrogen, C1-C20alkyl, C2-C4hydroxyalkyl or phenyl; exhibit an unexpectedly good performance in photopolymerization reactions.

Oxime ester photoinitiators

3,3‘-Diethylthiadicarbocyanine (DiSC2(5)) is a symmetrical cationic cyanine dye consisting of two N-ethylated benzothiazole groups linked by a pentamethine bridge. Spectroscopic analysis indicates dimerization of the dye in the presence of duplex DNA sequences consisting of alternating adenine/thymine (A/T) or inosine/cytosine (I/C) residues, based on the following observations:  (i) the absorption maximum shifts from 647 to 590 nm, (ii) exciton splitting is observed in the induced circular dichroism spectrum, and (iii) fluorescence from the dye is strongly quenched. Dimerization on I/C, but not G/C sequences indicates that the cyanine dimers insert into the minor groove, a conclusion that is supported by viscometric analysis. Spectroscopic studies with short synthetic oligonucleotide duplexes demonstrate that dimerization is highly cooperative:  binding of one dimer greatly facilitates binding of a second dimer. For longer binding sites, this cooperativity leads to the formation of extended helical cyani...

Spontaneous Assembly of Helical Cyanine Dye Aggregates on DNA Nanotemplates

Photoinitiators for free radical polymerization

Cyanine borate (R(Ph){sub 3}B{sup {minus}}; R = alkyl) salts dissolved in nonpolar solvents exist predominantly as ion pairs. Irradiation of the ion pair with visible light absorbed by the canine leads to formation of a locally excited singlet state of the dye. The singlet excited cyanine in the ion pair is capable of oxidizing the borate anion to the boranyl radical (R(Ph){sub 3}B{sm bullet}). The rate constant for this electron-transfer reactions (k{sub et}) depends on the free energy change ({Delta}G{sub et}). This latter value was estimated for a series of borates and the relationship between k{sub et} and {Delta}G{sub et} appears to give a maximum value consistent with the quadratic law predicted from Marcus theory. The boranyl radical undergoes carbon-boron bond cleavage to generate a free alkyl radical. The rate of bond cleavage depends directly on the stability of the alkyl radical formed. When stabilized alkyl radicals are formed, carbon-boron bond cleavage is faster than the back-electron-transfer reaction that regenerates the cyanine borate ion pair.

Photochemistry of carbocyanine alkyltriphenylborate salts: intra-ion-pair electron transfer and the chemistry of boranyl radicals

Photoinitiation of polymerization is a process of immense practical, economic, and theoretical importance. In typical examples the polymerization of an acrylate or styrene-derived monomer is initiated by irradiation of a sensitizer with ultraviolet light. The excited state of the sensitizer may dissociate directly to form active free radicals as in the case of the benzoin ethers, or it may first undergo a bimolecular electron-transfer reaction whose products initiate polymerization as is the case in the benzophenone-dimethylaniline system. Efforts to extend the range of useful photoinitiators of free-radical polymerization to the visible region of the spectrum have heretofore met with only modest success. These special initiators typically are sensitive only to blue light or suffer from thermal instability and have low quantum efficiencies. The authors report herein the discovery that triphenylalkylborate salts of cyanine dyes (Chart I) are photoinitiators of free-radical polymerization whose sensitivity throughout the entire visible spectral region is the result of a novel intra-ion-pair electron-transfer reaction.

Electron-transfer reactions in cyanine borate ion pairs: photopolymerization initiators sensitive to visible light

A substrate is coated with a visible light sensitive composition comprising a free radical addition polymerizable or cross linkable material and a photobleachable ionic dye-counter ion compound capable of absorbing visible light and generating free radicals. The composition is exposed to light to harden the composition, and to bleach the composition to an essentially colourless state. Also described are photohardenable compositions containing photobleachable ionic dye-counter ion compounds as photoinitiators useful in the aforesaid process.

Process for coating a substrate

A photohardenable composition comprises a free radical addition polymerizable or crosslinkable compound and an ionic dye-counter ion compound, said compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said compound. The use of such compositions in dentistry, for producing holograms, for producing three-dimensional models and for protecting or repairing underwater surfaces, is also described.

Peter Gottschalk

Papers

Photochemistry of carbocyanine alkyltriphenylborate salts: intra-ion-pair electron transfer and the chemistry of boranyl radicals

Electron-transfer reactions in cyanine borate ion pairs: photopolymerization initiators sensitive to visible light

Process for coating a substrate

Photosensitive compositions and materials

Electron-Transfer Reactions in Cyanine Borate Ion Pairs: Photopolymerization Initiators Sensitive to Visible Light.