Photoisomerization of trans-Stilbene in Poly(vinyl alcohol) and Importance of Solute–Polymer Interactions

We have measured the polarized absorption and picosecond transient absorption spectra of trans-stilbene in poly(vinyl alcohol) (PVA) films. We found that the dichroic ratio in the first absorption band and the lifetime of the S1 state increased as the hold-time was increased. The hold-time is the duration in which sample films were kept wet before they were dried. For similar values of the hold-time, the absorption spectra showed a red shift and slight sharpening. These results indicate that during the hold-time, solute–polymer interactions become strong; these interactions not only act as the orienting force during film stretching but also act as friction that opposes isomerization.