Citation
Yu, Zhou and Guo, Xiangru and Zhang, Qi and Chi, Lang and Chen, Ting and Xia, Ruidong and Wu, Longfei and Lüer, Larry and Cabanillas González, Juan
(2016).
Novel fluorene-based copolymers containing branched 2-Methyl-butyl-substituted fluorene-co-benzothiadiazole units for remarkable optical gain enhancement in green-yellow emission range.
"Journal of Physical Chemistry C", v. 120
;
pp. 11350-11358.
ISSN 1932-7447.
https://doi.org/10.1021/acs.jpcc.6b01375.
Abstract
We develop novel fluorene-based green-yellow emission copolymers (namely, nF1/4F8BT) composed of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and branched 2-methylbutyl substituted fluorene-co-benzothiadiazole units (F1/4BT) in different ratios. Upon blending nF1/4F8BT copolymers with poly(9,9-dioctylfluorene) (PFO), a systematic increase in photoluminescence quantum efficiency is observed as the ratio of the branched monomers increase. Likewise, nF1/4F8BT and PFO:nF1/4F8BT blends exhibit superior optical gain properties with respect to F8BT, manifested as a 30% reduction of amplified spontaneous emission threshold and 50% increase in optical gain with respect to F8BT blends at the same emission wavelength. The optical-gain-related properties were studied to understand the influence of the branched side chain unit on stimulated emission properties. Femtosecond transient absorption studies confirm exciton-annihilation hindrance in the new copolymers likely caused by interference of branched substituents with molecular packing in films. Branch side-chain substitution of a limited number of monomers is an efficient strategy to boost the optical gain properties of conjugated polymers.