Characterization of the molecular environment of polymer Langmuir-Blodgettfilms using a pyrene fluorescent probe

The molecular environment of polymer Langmuir-Blodgett (LB) films with diff erent alkyl chain length, poly(N-dodecyl acrylamide) (pDDA) and poly(tert-p entyl acrylamide) (ptPA), which are copolymerized with a small amount of 1- pyrenylmethyl acrylate (PyMA) comonomer as a luminescent probe, was investi gated by means of the surface pressure (pi)-area (A) isotherms, UV-vis spec troscopy, and fluorescence spectroscopy. The pyrene ring orients perpendicu lar to the p(DDA/PyMA) layer in both the monolayer at the air/water interfa ce and LB multilayers, while the pyrene moiety of p(tPA/PyMA) takes a paral lel orientation to its layer plane. The pyrene residue is more exposed to i ts surroundings in p(tPA/PyMA) LB films and therefore sensitive to solvent polarity. The measurement of fluorescence anisotropy confirmed that the pyr ene was densely packed in the LB films. These findings suggest that the mol ecular orientation of luminescent molecules can be controlled when the leng th of side chains is changed by only several angstroms in a polymer LB asse mbly system.