In Cage Mobility in Thin Polymer Films Probed by Single Molecule Spectral and Orientational Fluctuations

PEDRO F. ARAMENDÍA

Sarasota, Florida

Congreso; 22nd IAPS Meeting; 2013

Inter-American Photochemical Society

P { margin-bottom: 0.21cm; direction: ltr; color: rgb(0, 0, 0); widows: 2; orphans: 2; }P.western { font-family: "Times New Roman",serif; font-size: 12pt; }P.cjk { font-family: "Times New Roman",serif; font-size: 12pt; }P.ctl { font-family: "Times New Roman",serif; font-size: 12pt; } The in cage mobility of Nile Red embedded in nanometric thin films of poly(alkylmethacrylates) was studied by single molecule fluorescence microscopy. Fluorescence emission spectra were recorded as a function of time in different locations of the polymer film by confocal microscopy, in the 278−323 K temperature range. Three types of emission spectra were identified. The spectra with the highest emission energy spectra show small amplitude fluctuations. The other two types of emission profiles exchange more frequently. The fluctuations are analyzed by the complementary cumulative distribution function of spectral emission energy difference between successive spectra in a time trace. The fluctuations show three components: two of them with zero mean average and distinctly different standard deviations and a third component with much lower probability and an amplitude of 0.13−0.15 eV. The behavior of the spectral fluctuations is very similar in all conditions, pointing to a common feature of the probe−polymer cage as responsible for their presence. Orientational rearrangements of the fluorophores were monitored by polarized wide field emission of single molecules, as well as by polarized emission of bulk samples under polarized irradiation with photobleaching. in the same systems. We observe neat changes in the mobility behavior between polymer films and within the same polymer matrix with the film thickness that parallel the expected change in the glass transition temperature of the sample. The difference in behavior between the spectral and orientational fluctuations with the environment can be explained by the different space requirements of both types of variations.