title: Ordered fibrillar morphology of donor-acceptor conjugated copolymers at multiple scales via blending with flexible polymers and solvent vapor annealing: insight into photophysics and mechanism.
abstract: The ordered, aligned fibrillar morphology at multiple scales of a donor-acceptor (D-A) conjugated copolymer of 3,6-bis-(thiophen-2-yl)-N,N'-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole and thieno[3,2-b]thiophene (PDBT-TT) was prepared via blending with flexible polymers (PS13.7k, PDBT-TT/PS = 1/10 w/w) followed by chloroform (CF) solvent vapor annealing (SVA) for 24 h. The aligned fibrillar bundles were of about 500 nm width, consisting of parallel aligned nanofibrils of ab. 10 nm width. It was found that the direction of backbones in nanofibrils was parallel to the long axis of nanofibrils, which implied an intense intra-chain conjugation associated with extended backbones and J-aggregation of PDBT-TT. This ordered morphology corresponded to the characteristic photophysical features of (i) red-shifted absorption arising from J-aggregation, (ii) larger Davydov splitting, (iii) the prevailing absorbance of J-aggregation over H-aggregation in its UV-Vis spectrum and (iv) more red-shifted max photoluminescence emission, compared with the films prepared via the other methods. By investigating the Raman spectra and XRD profiles, it is proposed that the origin of the best morphological and photophysical order is the combination of blending and SVA. The limited and "flexible" space formed due to phase separation between PDBT-TT and PS facilitated the motion of rigid PDBT-TT chains and promoted their stacking order as templates, and CF vapor assisted the conformational transition of chains to more "coil-like" to help them reorganize in a thermodynamic stable way.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, P. R. China. ychan@ciac.ac.cn.
authors.forename: Haiyang
authors.initials: H
authors.lastname: Wang
authors.forename: Jiangang
authors.initials: J
authors.lastname: Liu
authors.forename: Yaozhuo
authors.initials: Y
authors.lastname: Xu
authors.forename: Xinhong
authors.initials: X
authors.lastname: Yu
authors.forename: Rubo
authors.initials: R
authors.lastname: Xing
authors.forename: Yanchun
authors.initials: Y
authors.lastname: Han