From Event: SPIE Organic Photonics + Electronics, 2015
We used steady state and picosecond transient photoinduced absorption (PA),
excitation dependence (EXPA(ω)) spectrum of the triplet exciton PA band, and its
magneto-PA (MPA(B)) response to investigate singlet fission (SF) of hot-excitons into
two separated triplet excitons in luminescent π-conjugated polymers. From the high
energy step in the triplet EXPA(ω) spectrum of poly(dioctyloxy)-phenylenevinylene
(DOO-PPV) films, we identified a hot-exciton SF (HE-SF) process having threshold
energy at E≈2ET (=2.8 eV, where ET is the energy of the lowest lying triplet exciton),
which is about 0.8 eV above the lowest singlet exciton energy. The picosecond
transient PA with 3.1 eV pump excitation shows that in DOO-PPV film a triplet
exciton is generated at time, t<500 ps. However the ultrafast triplet generation is
missing in DOO-PPV solution, indicating that the HE-SF is predominantly interchain
in nature. The HE-SF process was confirmed by the triplet MPA(B) response for
excitation at E>2ET, which shows a typical SF response. Our work shows that the SF
process in π-conjugated polymers is a much more general process than thought
Yaxin Zhai, Ella Olejnik, and Z. Valy Vardeny, "Optical and magnetic probes of hot singlet exciton fission in pi-conjugated polymers for organic photovoltaic applications," Proc. SPIE 9564, Light Manipulating Organic Materials and Devices II, 95640A (Presented at SPIE Organic Photonics + Electronics: August 12, 2015; Published: 5 September 2015); https://doi.org/10.1117/12.2187596.
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