Tj. Cleij et Lw. Jenneskens, Nonionic water-soluble polysilanes: Global conformation in solution and the occurrence of preferential solvation, J PHYS CH B, 104(10), 2000, pp. 2237-2241
In aqueous solution UV-absorption and fluorescence emission spectroscopy re
veal that the nonionic water-soluble polysilanes poly(4,7,10-trioxaundecylm
ethylsilane) (1) and poly(4,7,10,13-tetraoxatetradecylmethylsilane) (2) are
present in a highly folded random coil. In contrast, in organic solvents t
he backbone adopts a more extended conformation. These changes in backbone
conformation are accompanied by changes in the average backbone silicon seg
mental length L from 15 to 21-24. Concomitantly, the exciton coherence leng
th also exhibits a 2-fold increase. The results obtained for 1 and 2 are co
mpared to those of poly(4,7,10-trioxahexadecylmethylsilane) (3) and poly(4,
7,10,13-tetraoxanonadecylmethylsilane) (4), which contain instead of a CH3,
a C6H13 moiety as the side chain end group. A detailed analysis of aqueous
/organic binary solvent mixtures of 2 reveals that already a low mole fract
ion of the organic solvent induces large shifts in the photophysical proper
ties; i.e., preferential solvation occurs at a mole fraction of ca. 0.15, H
ence upon addition of small amounts of organic solvents, the solute-solvent
interactions, which in H2O prevent the silicon backbone from adopting a mo
re extended conformation, an reduced, causing the backbone to be less disto
rted. This is supported by the increase in the quantum yield Phi in going f
rom polar aqueous to apolar organic solvents.