Exciton Relaxation in PDA-4BCMU: From Crystals to Films

Adjusting the Third-Order Nonlinear Optical Properties of a Conjugated Polymer Film

“…Particularly striking are chromic effects that reflect conformational disorder on length scales shorter than the size of a relaxed exciton on a crystalline polydiacetylene chain. For example, blue single crystals of poly(4BCMU) turn red on exposure to solvent vapors, and form yellow solutions in good solvents …”

“…The linear vibrational and electronic responses of polydiacetylenes provide important information on the conformation and orientation of the polymer backbone (Figure ) and side groups (Figure ). Both the center frequency and the bandwidth of the π → π* electronic transition, localized on the polymer backbone, depend on the processing history of the material, and we can exploit this relationship to characterize and quantitate the extent of backbone disorder in the polymer . We use anisotropy in the electronic response to infer the extent of backbone ordering in stretch aligned poly(4BCMU).…”

“…For the elongation ratio, l / l 0 , spanning the range of 1 (unstretched) to ∼5, we measure a corresponding variation in α ∥ /α ⊥ from 1 to 2.5. To put these values in perspective, disordering a single crystal with α ∥ /α ⊥ ∼ 50 by exposure to solvent vapor reduces α ∥ /α ⊥ to 5 …”