Adsorbed polymer photophysics

Several papers compare the properties of sulfobetaine (meth)acrylic polymers. NMR spectra and solution properties of 23a and 23b [59,60] are correlated with data from the corresponding polycarbobetaines [26]. The photophysical and solution properties of pyrene-labeled 23c were studied in terms of fluorescence emission. Addition of surfactants induces the formation of mixed micelles in aqueous solution [61]. Excluded volume effects of the unlabeled polymer were measured by light scattering [62], its adsorption on silica was studied by adsorbance measurement and ellipsometry [62,63], and the electrostimulated shift of the precipitation temperature was followed at various electric held intensities [64]. Polysulfobetaines may accelerate interionic reactions, e.g., oxidation of ferrocyanide by persulfate [65]. The thermal and dielectric properties of polysulfobetaines 23d were investigated. The flexible lateral chain of the polymers decreased Tg, for which a linear relationship with the number of C atoms was shown [66,67]. 

Cellulose. Cellulose has been used as a solid powdered substrate for the study of photophysical and photochemical studies of several organic probes, mostly dyes. Some of the properties of this substrate, namely the capacity of adsorbing molecules both by entrapment and on the surface of the natural polymer (forming in many cases hydrogen bonds) and also the absence (or extremely reduced) of diffusion of oxygen, make this substrate a particularly attractive one for room temperature luminescence studies [75-83]. We recently published some fluorescence and phosphorescence studies of rhodamine dyes [15,81,82], auramine O [81b], 2,3-naphthalimides [84], oxazine [85], acridine orange [86], and cyanine dyes [16, 87, 88] adsorbed on cellulose. 

The photochemical and photophysical behavior of azobenzene adsorbed on polymer or silica films has been reported recently " azobenzene adsorbed in water-swollen Nafion-H+ (Nafion is a polymer consisting of a perfluorinated backbone and short pendant chains terminated by sulfonic acid groups) exhibited strong fluorescence. The irradiation resulted in the formation of benzo[c]cinnoline and benzidine in quantitative yield, while azobenzene incorporated into a methanol-swollen Nafion-H+ membrane did not emit fluorescence but merely underwent E,Z-isomerization. Thus, solvent-swollen Nafion is useful in the selective phototransformation of azobenzene. According to the authors, protonated azobenzene molecules are located at the fluorocarbon/water interface in water-swollen Nafion-H+ Z-Azobenzene formed on these membranes resulted in cychzation to give the observed products (Scheme 52). 

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