Field enhanced photoluminescence of isolated chains of 3BCMU in their monomer single crystals

Monomer single crystals of 3BCMU (poly 5,7-dodecadiyne-1,12 diol-bis(3-butoxy-carbonyl-methylurethane)) contain in addition to a small amount of blue polymer chains with excitons at 1.9 eV, a very small fraction of conjugated bonds with excitons at 2.28 eV detected by their resonant and strong fluorescence. We studied their behavior in electric fields and found in electroabsorption spectra, the quadratic Stark shift common to polydiacetylene. The luminescence responds to electric fields by significant enhancement by a few percent in fields which are too small to observe the Stark effect. The enhancement increase is sublinear with field and is attributed to excitons generated by carriers injected from band states of regular blue chains into chain segments of different confirmation.