Observation of the missing mode effect in a poly-phenylenevinylene derivative: effect of solvent, chain packing, and composition.
J Chem Phys
; 133(17): 174901, 2010 Nov 07.
Article
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| MEDLINE
| ID: mdl-21054063
ABSTRACT
Optical emission spectra of poly[2-methoxy-5-[3('),7(')-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) in dilute solutions exhibit a vibronic progression interval (â¼1225 cm(-1)) that does not correspond to any ground state vibrational mode frequency. This phenomenon is assigned as the missing mode effect (MIME) in which five key displaced polymer backbone vibrational modes in the range of 800-1600 cm(-1) contribute to the MIME interval. Emission spectra are calculated by analytically solving the time-dependent Schrödinger equation using estimates of mode-specific vibrational displacements determined independently from preresonance Raman intensities. Emission spectra of MDMO-PPV thin films and nanoparticles are measured and lineshapes show an increase of the MIME frequency to â¼1340 cm(-1) in addition to changes in vibronic intensity distributions and energies. Composite blend thin films consisting of MDMO-PPV and a fullerene derivative (11 w/w) exhibit a substantially larger MIME interval (â¼1450 cm(-1)) that arises from an increase in polymer chain planarity. This structural change is most apparent from large decreases of the excited state displacement of an out-of-plane C-H bending mode (961 cm(-1)) that becomes forbidden in the planar structure.
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2010
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