title: Conformation-Dependent Photostability among and within Single Conjugated Polymers.
abstract: The relationship between photostability and conformation of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) conjugated polymers was studied via excitation polarization modulation depth (M) measurements. Upon partial photobleaching, M distributions of collapsed, highly ordered MEH-PPV molecules shifted toward lower values. Conversely, M distributions of MEH-PPV molecules with random coil conformations moved toward higher values after partial photobleaching. Monte Carlo simulations of randomly distributed dipole moments along polymer chains subjected to partial photobleaching revealed that a statistical effect leads to an increase in peak M value. Decreases in M values seen experimentally in the population of MEH-PPV molecules with high M values, however, are due to conformation-dependent photostability within single MEH-PPV polymers. We show that, while folded MEH-PPV molecules are relatively more photostable than extended MEH-PPV molecules in an ensemble, extended portions of particular molecules are more photostable than folded domains within single MEH-PPV molecules.
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Heungman
authors.initials: H
authors.lastname: Park
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Dat Tien
authors.initials: DT
authors.lastname: Hoang
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.|Department of Chemistry, Sungkyunkwan University , Suwon 440-746, Republic of Korea.
authors.forename: Keewook
authors.initials: K
authors.lastname: Paeng
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Jaesung
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Kaufman
keywords: Conjugated polymer; MEH-PPV; exciton migration; fluorescence; modulation depth; photobleaching