Microstructural Variation upon Introducing Di([2,2'-bithiophen]-5-yl)pyrenes into a Naphthalene Diimide-Based Polymer

Four pyrene-based conjugated molecules1,6-bis-(bithiophene)-pyrene (A), 1,6-bis-[5-octyl-(2,2'-bithiophen)-5'-yl]-pyrene (B), 2,7-bis-[5-octyl-(2,2'-bithiophen)-5'-yl]-pyrene (C), and 4,9-bis-[5-octyl-(2,2'-bithiophen)-5'-yl]-pyrene (D)have been designed, synthesized, and blended with poly-[[1,2,3,6,7,8-hexahydro-2,7-bis-(2-octyldodecyl)-1,3,6,8-dioxobenzo-[lmn]-[3,8]-phenanthroline-4,9-diyl]-[2,2'-bithiophene]-5,5'-diyl] (P-(NDI2OD-T2, P). The structural difference between A and B lies in the presence of an alkyl substituent, while B, C, and D are regioisomers. The effects of the alkyl substituent and regioisomerism on the microstructure of P have been investigated. Differential scanning calorimetry and ¹H NMR spectroscopy suggest that alkyl substitution may not play a significant role in determining the crystallization and aggregation of P. In contrast, regioisomerism significantly influences these properties. Grazing-incidence X-ray scattering indicates that while the alkyl substituent affects lamellar stacking, regioisomerism plays a crucial role in shaping the polymer's microstructure. The introduction of pyrene enhances polymer backbone rigidification, likely due to the establishment of naphthalene diimide-pyrene interactions, as supported by density functional theory calculations. Organic field-effect transistor measurements reveal that the blends can exhibit higher electron mobility (μ_e) than P. Linear regression analysis suggests that the crystallization of P is correlated with μ_e. Lastly, the current blending approach is compared with the previous incorporation approach, highlighting the role of molecular degrees of freedom in contributing to the observed differences.