Photochemical hole burning study of unimacromolecular micelles with controlled radii embedded in poly(vinyl alcohol)

摘要

The highly constrained microenvironment and the dependence of the structural relaxation and electron-phonon interaction on the distance between the chromophores and the matrix around them in unimolecular micelles (unimers) of amphiphilic random terpolymers containing sodium sulfonate, cyclododecyl (CD) and a small amount of tetraphenylporphine (H_2TPP) groups were studied at low temperatures using photochemical hole burning spectroscopy. The radii of the terpolymers micelles were controlled, and they were embedded in poly(vinyl alcohol). The terpolymers with CD groups form unimers in the polymer matrix. We also measured the homopolymers containing CD or sodium sulfonate groups doped with H_2TPP or sodium salt of sulfonated tetraphenylporphine (TPPS). The burned holes were thermally more stable in the unimer with CD clusters than those both in CD homopolymers and in the hypothetical system where the sodium sulfonate and CD groups are randomly dispersed. The results were attributed to the "pinning down" of the H_2TPP species to constrained configurations in the CD cluster. The phonon frequency and the inhomogeneous width are independent of the micelle's radii in the present experiment condition. Then we conclude that the electron-phonon interaction and intermolecular interaction including van der Waals interaction and dipole-dipole interaction are effective within 2.3 nm in the present system.