Femtosecond study of exciton dynamics in polyfluorene statistical copolymers in solutions and thin films

Jin Z. Zhang; Melissa A. Kreger; Gerrit Klaerner; M. Kreyenschmidt; Robert D. Miller; J. Campbell Scott

doi:10.1117/12.284150

1 December 1997 Femtosecond study of exciton dynamics in polyfluorene statistical copolymers in solutions and thin films

Jin Z. Zhang, Melissa A. Kreger, Gerrit Klaerner, M. Kreyenschmidt, Robert D. Miller, J. Campbell Scott

Author Affiliations +

Proceedings Volume 3145, Optical Probes of Conjugated Polymers; (1997) https://doi.org/10.1117/12.284150
Event: Optical Science, Engineering and Instrumentation '97, 1997, San Diego, CA, United States

Abstract

The formation and decay dynamics of photogenerated excitons in polyfluorene statistical co-polymers in solutions and in thin films have been studied using femtosecond transient absorption spectroscopy. In solution photoexcitation of the polymer generates primarily intrachain singlet excitons which are initially hot and then relax quickly (< 200 fs) towards the equilibrium position in the excited state. The exciton subsequently decays following a double exponential with time constants of 30 ps and 330 ps in toluene. The fast decay is attributable to vibrational relaxation, spectral diffusion, or internal conversion (recombination) of the exciton from the excited to the ground electronic state through tunneling or thermal-activated barrier crossing before thermalization. The slow decay is assigned to conversion of the thermalized exciton to the ground state through both radiative and non-radiative pathways. In films the exciton dynamics are found to depend strongly on excitation intensity. At low intensity, the dynamics are similar to that in solutions, with a double exponential decay with time constants of 15 ps and 300 ps. At high intensities, a fast decay component with a time constant of 0.8 ps appears, which becomes more dominant at higher intensities. This fast decay is attributed to exciton- exciton annihilation due to high density of excitons created. The signal in films at both low and high excitation intensities is attributable to intrachain singlet excitons, as in solution. There is no evidence for formation of interchain bound polaron pairs in films at low intensities. At high intensities, the possibility cannot be ruled out completely, especially in relation to the fast decay. If bound polaron pairs are formed as indicated by the fast decay, they must be generated as a result of interaction between excitons on different chains since they are absent at low power, an they must be created and then decay within about 1 ps.

Citation Download Citation

Jin Z. Zhang, Melissa A. Kreger, Gerrit Klaerner, M. Kreyenschmidt, Robert D. Miller, and J. Campbell Scott "Femtosecond study of exciton dynamics in polyfluorene statistical copolymers in solutions and thin films", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); https://doi.org/10.1117/12.284150

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available