Dynamics of triplet excitons in MEH-PPV measured by two-photon photoemission
نویسندگان
چکیده
We have used two-photon photoemission to probe the dynamics of the long-lived triplet excitons in pristine and photo-oxidized lms of poly[2-methoxy,5-(2'-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV). We use a rate equation model to explain the intensity dependence of the total photoelectron yield in terms of the relaxation dynamics of the triplet excitons. Observations of the pristine lms indicate that triplet-triplet annihilation is an important deexcitation mechanism for photoexcited triplet excitons in MEH-PPV. Upon photo-oxidation, the measured triplet exciton energy is shifted downward and the triplet exciton-derived photoemission linewidth is dramatically narrowed. Both of these e ects are attributed to modi cation of the physical and electronic structure of the lms arising from the formation of carbonyl defects on the polymer chains. We also observe signi cant oxygen-induced lifetime quenching of the triplet exciton.
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