Photochromism of Molecular Assembly

4 -Viologens exchanged with benzene sulfonate anions having long alkyl side chains (V2+2ArS03 ) possess relatively low melting points and afford transparent 

The color species developed by near-UV light are hardly affected by irradiation with visible light, suggesting that the back electron transfer is thermal in nature. This is promising for photo-memory, that is, color development by photon-mode and heat-mode bleaching. 

Since photoelectron transfer of viologens proceeds from counteranions to dications in spite of the large difference of dark redox potentials between both 

Benesi-Hildebrandt plots were linear in a low concentration range however, the linear relationship did not exist between the transition energies and the difference in the half-redox potential of 2V. The solvation of 2,2 -bipyridinium dication is relatively small compared with that of the 4,4 -isomer possessing a symmetrical molecular structure. This decreases the electrostatic interaction to lead to a low transition energy. The CT bands for Bu-V2+ and Bzl-V2+ with [Fe(CN)6]4 ions almost linearly increase in an absorbance upon near-UV irradiation, and the absorbance decreases progressively in the dark and even more rapidly upon heating. 

The films cast from an aqueous polymer solution of these [Fe(CN)6] complexes became opaque with evaporating water in the polymer solution due to the low 

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