Three-arm poly(dimethylsiloxane) junction bearing a single pendant dansyl group: A model architecture for polymer junction points dissolved in liquids and molten polymers

We have determined the static and time-resolved fluorescence of a poly(dimethylsiloxane) (PDMS)-based three-armed junction that contains a single dansyl reporter group when it is dissolved at low concentration in three normal liquids (good, Theta, and poor solvents) and neat methyl-terminated PDMS. The junction results are compared to a junctionless analogue--dansyl propylamine. We report on the activation energies for dansyl thermal quenching and rotational reorientation and the dansyl residue's ability to reorient and precess at the junction point. In normal liquids a decrease in solvent quality leads to a collapse of the junction's PDMS arms around the dansyl reporter group, an inhibition of the dansyl residue's ability to form its twisted intramolecular charge transfer state, and impedance of the dansyl residue's ability to reorient. When the junction is dissolved in neat methyl-terminated PDMS, there is evidence for chain-length-dependent interpenetration of the PDMS solvent molecules into the junction and modulation of the local microenvironment surrounding the dansyl residue at the junction. These results demonstrate the dramatic role solvent can play in tuning the local microenvironment that surrounds a polymeric junction point.