Rose bengal polymer

Every polymer, no matter what the rose bengal concentration, shows a maximum absorption for the rose bengal moiety at 571-2 nn when the spectrum is taken in a non-polar solvent such as methylene chloride. RB benzyl ester, on the other hand, shows a maximum absorption at 564 nm in MeOH. This phenomenon is explained by a relatively large influence of hydrogen bonding solvents on the absorption maxima. The absorption maximum of RB benzyl ester (essentially a monomeric rose bengal polymer unit) in different solvents was measured. The positions of the absorption maxima, as a function of solvent, are shown in Thble IV. 

Neckers, D.C. (1988) Properties of Polymeric Rose Bengals - Polymers as Photochemical Reagents, in Synthesis and Separations Using Functional Polymers (eds D.C. Sherrington and P. Hodge), John Wiley Sons, Inc., New York, pp. 209-26. 

Polymer Rose Bengal was synthesized using Merrifield chemistry [296] from chloromethylated polystyrene beads [297] and has quantum yields of singlet oxygen formation about the same as does Rose Bengal in similar solvents. It does not bleach, does not undergo self-quenching, and therefore seems not susceptible to electron transfer between dye molecules, a phenomenon induced by dye site isolation on the backbone of the polymer. 

Among the more interesting applications of polymer Rose Bengal is that of a sensitizer in studying the oxidation of other polymeric substrates [301]. Rose Bengal immobilized on Sepharose has been reported as a sensitizer for protein photooxidation [302], The oxygen uptake by the amino acids cysteine, hisitidine, methionine, tryptophan, and tyrosine was reported to be about 20% as much from the immobilized dye as from the free dye in aqueous solution. 

As a matter of convention, (g) -rose bengal refers to rose bengal iimobilized on insoluble crosslinked styrene-oo-divinylbenzene beads. All other polymers referred to are not crosslinked and hence soluble in various solvents. 

Polymer rose bengal, or Sensitox I, was derived from this concept. It was, in the words of an inmortal reviewer, a "citation classic".17... 

Until the beginning of this work, little was known about the effect of the polymer on the behavior of the sensitizer, rose bengal. In this paper we shall establish that the polymer is indeed an extremely important component of the chemistry of polymeric derivatives of rose bengal. 

The initial polymer rose bengal was prepared from chloro-methylated polystyrene/divinylbenzene beads using the following reactions... 

The results of several control experiments made it clear that polymer rose bengal was an authentic singlet oxygen sensitizer.1 Photooxidation of typical singlet oxygen acceptors in non-polar... 

It was our intention when this new work began to outline, more fully, the effect of the polymeric structure on the effectiveness of rose bengal as a photosensitizer and to compare the behavior of the polymer-bound dye to the behavior of the dye - free - in solution. In the present paper, therefore, we report on the photochemical and spectral properties of new singlet oxygen sensitizers based on soluble polystyrenes. These new derivatives are referred to as P -RB. 

Because of the substantial excess of chloramethyl groups in the polymer relative to the quantity of added rose bengal (Table II), it could be assumed that all of the RB becomes attached to the polymer chain. The previous elegant work of Iamberts and Neckers ... 

The resultant polymeric rose bengals are soluble in solvents like methylene chloride and chloroform, but are not soluble in MeOH with the exception of P -RB- 1520 vrtiich is soluble in a mixture of MeOH/CH2Cl2 (1 1). In addition all of the polymers show the typical carbonyl absorption of an ester between 1725 and 1741 am-1. 

This indicated that the polymer degradation process was likely sensitized by monomeric rather than polymeric rose bengal. 

These polymers separate into three groups which have different electronic absorption properties. Hie first is P-RB-51, the lowest in rose bengal content. This polymer has an Axi/A 2 ratio which is very similar to the ratio of A)i/A>2 for RB (Figure 2). The second group of polymers P-RB-102, P-RB-152, and P-RB-305 has a ratio of the two absorption maxima, A, p/A, which is very similar to, but lower than that of either P-RB-51 or RB. The last group of polymers shows a reduction in the ratio of A /A In this case, the amount of RB attached to the polymer is much larger by comparison. 

It is clear that as the amount of rose bengal attached to the polymeric support increased in the regime where the polymer can be called "lightly functionalized", the quantum yield of singlet oxygen formation increases also, reaching a maximum value for the... 

As the loading of the polymer is increased, the actual amount of polymer required to achieve a fixed concentration of rose bengal in the solvent became less. More polymer is dissolved in the solution in the lower loading case, hence the solution is more viscous. 

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