Influence of the Glass Transition on Rotational Dynamics of Dyes in Thin Polymer Films. Single Molecule and Ensemble Experiments

ARÁOZ, BEATRIZ; CARATTINO, AQUILES; DANIELA TÄUBER; CHRISTIAN VON BORCZYSKOWSKI; PEDRO F. ARAMENDÍA

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2014 vol. 118 p. 10309 - 10317

1089-5639

We performed polarized fluorescence emission studies of Nile Red (NR) in poly-(methylmethacrylate)(PMMA),poly-(ethylmethacrylate)(PEMA),andpoly-(butylmethacrylate), (PBMA), at the single molecule (SM) and at the ensemble level, to studythe in cage movements of the ground state molecule in polymer films of nanometric thicknessat room temperature. Experiments were performed with wide field irradiation. At theensemble level, the linearly polarized irradiation was used to induce a photoselection bybleaching, which is compensated by rotational diffusion. Both results show an appreciabledifference in mobility of NR in the films that is correlated with the different glass transitiontemperatures of the films, particularly in PEMA, which displays a clearly distinct behaviorbetween the 200 nm films, representing a rigid environment, and the 25 nm ones, showingmuch higher mobility. We developed a model of broad application for polarizedphotobleaching that allows obtaining rotational diffusion coefficients and photobleachingquantum yields in an easy way from ensemble experiments. The parameters obtained fromensemble measurements correlate well with the results from single molecule experiments.