A series of alternating co-polymers were synthesized, composed of tetra-phenylenevinylene derivatives and 2- and 4-carbon tethers.  Static absorption and photoluminescence of drop-cast films show that while the monomeric control and the 4-carbon tethered system exhibit a redshift in absorption and quenched fluorescence after thermal annealing, the 2-carbon tethered system shows little change after annealing, favoring a highly fluorescent film.  Time-resolved photoluminescence measurements support this trend: the fluorescent decay of the monomeric control and 4-carbon linked system is expedited to favor a faster relaxation pathway (10 ns) both before and after thermal annealing.  TEM images reveal that while the monomer and 4-carbon tethered system form crystalline features during annealing, the morphological characteristics of the 2-carbon tethered system are trapped after film casting; the annealing process produces no alterations to the amorphous pattern afforded in the as-cast film. Geometry optimization calculations of the 2- and 4-carbon systems shed light on experimental data; the 2-carbon tether is too short to allow intramolecular p-stacking between neighboring phenylenevinylene units to occur at a distance typically found in similar oligomers, which may hinder the ability of the polymer to reorganize during annealing. The vast differences imparted by small modifications to the tether length may provide a method of fine-tuning the photophysics and morphological features within the thin films of other polymeric species.

Carpenter's rule polymers: Morphological and photophysical response in tethered oligo-phenylenevinylenes as a function of linker length

247th National Meeting (2014)

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