Rose bengal singlet oxygen formation

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. 

Table I. Visible Absorption Spectra and Quantum Yields of Singlet Oxygen Formation of Rose Bengal Derivatives...

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... 

Both curves have similar shapes and it is clear that the photooxidation process is controlled by the diffusion of oxygen into the rose bengal sites in the polymer solution. These results suggest that when a snail amount of rose bengal is attached to the polymeric backbone (P-RB-51, 102 152 305) the quantum yield of of singlet oxygen formation is essentially the same (about 0.38). 

Quantum yields of singlet oxygen formation from polymer rose bengals are essentially the same as are quantum yields of singlet oxygen formation in solution (15). 

We have studied the effect of dye/dye interactions on singlet oxygen formation both in soluble polymers and with polymer beads. Rose bengal is our probe. 

Rose bengal loading on Merrifield beads does not affect the quantum yield of singlet oxygen formation sigi icantly, Table IV. The highest observed value is 0.91 (for ( )-RB-0.4) other values are only 15% lower, e.g. 0.76 for -RB-0.2). 

Table IV. Quantum Yield for Singlet Oxygen Formation for ( in CH2CI2 with Various Rose Bengal Loading...

We observed that if an amine is used as the cation at C-6, it has significant influence on the quantum yield of singlet oxygen formation from the polymer-based reagent. The observed efficiency of singlet oxygen formation from -rose bengals in which different ammonium ions are substituted at C-6 is shown in Table V. 

The situation differs when the rose bengal moiety itself is soluble in non-polar solvent as it is in the case of the appended rose bengal C-6 triethylammonium salt. When the C-2 (polystyry1) ester is converted to the C-6 ammonium salt, the solubility of the appended moiety in non-polar solvents is increased, the efficiency of singlet oxygen formation is now limited by (a) the effective isolation of the polymer appended dye and (b) by the possibility of formation of the dissociated form, i.e. by equilibrium between the protonated phenol group and dissociated... 

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