posted on 2018-11-02, 00:00authored byBradley Keller, Zhengxu Cai, Angelar K. Muthike, Prabhat Kumar Sahu, Hyungjun Kim, Audrey Eshun, Paul M. Zimmerman, Deqing Zhang, Theodore Goodson
New
donor–acceptor light harvesting polymers with either a 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene or a 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithienothiophene
donor subunit and either a 2-(nonadecan-9-yl)-5-(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, (E)-1,1′-bis(2-octyldodecyl)-[3,3′-biindolinylidene]-2,2′-dione,
or 3-ethyl-1-(thieno[3,4-b]thiophen-2-yl)heptan-1-one
acceptor were synthesized. In this study, the effects of donor conjugation
length and donor-acceptor combination on the optical properties of
the synthesized polymers were investigated using steady state, up-conversion,
quantum chemical simulations and ultrafast and transient spectroscopic
techniques. At high energies, it was observed that polymers with extended
donor conjugation had significantly enhanced absorption, whereas those
with stronger acceptors showed higher extinction coefficients at lower
energies. Fluorescence up-conversion experiments revealed that the
donor conjugation length increased the fluorescence lifetimes for
the extended conjugated polymers. Two-photon absorption experiments
and quantum chemical simulations showed that polymers with stronger
acceptors exhibited enhanced charge-transfer characteristics. Transient
absorption investigations revealed new optical species for the extended
donor polymers. This study has shown the considerable effect that
donor conjugation has on the optical properties of donor–acceptor
light harvesting conjugated polymers. The results from this work can
be used in the design and synthesis of new donor–acceptor polymers
for organic photovoltaics.