We have used two-photon photoemission to probe the dynamics of the long-lived triplet excitons in pristine and photo- oxidized films 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 films 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 effects are attributed to modification of the physical and electronic structure of the films arising from the formation of carbonyl defects on the polymer chains. We also observe significant oxygen-induced lifetime quenching of the triplet exciton.

Date Published: 1 December 1997
PDF: 11 pages
Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); doi: 10.1117/12.284147

Published in SPIE Proceedings Vol. 3145:
Optical Probes of Conjugated Polymers
Z. Valy Vardeny; Lewis J. Rothberg, Editor(s)