Solid‐State Chemistry of Cyanine‐Type Dyes and the Effect of Two Novel Counterions on Their Crystal Properties

Abstract

Organic dyes undergo a variety of solid‐state chemical processes, including intra‐ and intermolecular reactions, gas‐solid reactions, and polymorphic transformations. The properties of dye solids are markedly affected by this chemistry. This paper reviews solid state dye chemistry from the literature and reports in detail the chemistry of two novel cyanine dye salts whose properties are controlled by the nature of their counterions. In cyanine‐oxonol salts, the oxonol counterion is a large planar dye which forms crystalline dye aggregates with cyanine ions. There is a multiplicity of polymorphic forms of these mixed dyes reflecting multiple favorable dye aggregate geometries. The cyanine‐borate salts undergo intermolecular solid‐state reactions. In either large single crystals or dispersions of the latter salts in polymer binders, alkyl transfer from the anion to the chromophore can be induced thermally or photochemically.

Tetraarylborates {[Ar]4B-}: estimation of oxidation potentials and reorganization energies from electron-transfer rates

“…1H NMR (200 MHz, CD3CN): 6 To an ether solution of tolylmagnesium bromide was added 0.5 equiv of dichlorophenyl boron, and the solution was heated at reflux overnight. 1H NMR (200 MHz, CD3CN): 6 To an ether solution of tolylmagnesium bromide was added 0.5 equiv of dichlorophenyl boron, and the solution was heated at reflux overnight.…”

Ultrafast charge transfer in solid-state films of pristine cyanine borate and blends with fullerene

“…The picosecond time scale for electron transfer from the tetraphenylborate moiety to the excited Cy3 suggested from the global analysis is in accordance with previous ndings in solution. 19,20 No evidence for tetraphenylborate radicals due to carbon-boron bond cleavage has been noticed as the cyanine reduced species absorbing at 420-450 nm recombines with the oxidized tetraphenylborate on the microsecond time scale. The widely used PCBM electron acceptor was blended with Cy3-B with different ratios and we found that the phase morphology drives charge injection in PCBM.…”

“…The photophysical properties of cyanine dyes have been extensively studied in solution [15][16][17] and in pristine solidstate lms. [18][19][20] Cy3 excited state dynamics in solution are strongly dependent on the nature of the counter-anion. [21][22][23][24][25] Cy3 hexauorophosphate (Cy3-P) tends to photoisomerize to the cisisomer and has a rather poor uorescence quantum yield.…”

Photoinduced electron transfer (PET) bond cleavage reactions

“…More recently, Schuster [25] has demonstrated that cyanine dyes, i.e., cyanine borates or cyanine dye-borate mixtures, provide visible light activated initiation of free radical polymerization [26]. The photoexeited cyanine dye oxidizes alkyltriphenylborates by PET to produce the bleached reduced cyanine along with an alkyl radical.…”