Abstract
The photophysical behaviour of the dye pseudoisocyanine (PIC) was studied in macromolecular (sodium alginate) and hydrotropic (sodium toluenesulphonate and sodium styrenesulphonate) solutions. It was found that the placement of the dye in these media affected the spectroscopic properties and the lifetimes of its excited states. The effects are traced down to the interactions of the dye molecules with the macromolecules or their placement in the hydrotropic aggregates, inducing the formation of J-aggregates of the dye or constraining its internal movements reducing the rate of internal conversion. The lifetimes of the triplet state of the dye in alginate were of the order of 20-30 ns in freshly prepared solutions, whereas when leaving the solution to rest for some hours the decay became biexponential with the growing of a species with lifetime around 150 ns. The latter is assigned to dye molecules placed in the alginate network.
Highlights
The photophysics of the cyanine known as pseudoisocyanine (PIC) has a relative long history due to its early use as a spectral sensitizer in photography.[1]
As expected, the emission (Figure 1b) increases with solvent viscosity, due to the increasing medium rigidity that reduces the rotation of the aromatic rings around the methine bridge, diminishing the internal conversion deactivation of the excited singlet state
The selected concentration range encompasses the minimum hydrotropic concentration (MHC) regions for these hydrotropes, which is around 1.0 mol L–1 for TS and 0.1 mol L–1 for StyS.[23]
Summary
The photophysics of the cyanine known as pseudoisocyanine (PIC) has a relative long history due to its early use as a spectral sensitizer in photography.[1] Its photophysics is well known.[2,3,4] The monomer band appears around 520 nm with a vibronic shoulder at 490 nm and a smaller one at 460 nm.[3] The decrease of the monomer band with increasing dye concentration is accompanied by the appearance of a band at ca. The dye 1,1’-methylene-2,2’-cyanine, whose structure differs from PIC only by the rigid linkage of the aromatic rings, has high emission intensity even in fluid media at room temperature.[18]
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