Supramolecular cocrystals built through redox-triggered ion intercalation in π-conjugated polymers

Abstract

Self-organization in π-conjugated polymers gives rise to a highly ordered lamellar structure, in which inter-chain stacking spontaneously forms two-dimensional conjugated sheets. This multi-layer stacked nature of semicrystalline polymers allows the inclusion of various functional molecules. In particular, redox-triggered ion-intercalation is an ideal system for molecular doping, for which extremely high charge carrier density has been achieved. Here, we conducted a detailed structural analysis and electron density simulation to pinpoint exactly where the guest dopants are located periodically in the void space in a polymer’s lamellae. Our findings are indicative of an intercalation compound of layered polymers and a guest intercalant. We show that a homogeneous cocrystal structure can be realized throughout the host polymer medium, which is proved by the observation of coherent carrier transport. The intercalation cocrystal nature gives the best achievable doping level in semicrystalline polymers and excellent environmental stability. These findings should open up possibilities for tuning the collective dynamics of functional molecules through intercalation phenomena.

Strong and Atmospherically Stable Dicationic Oxidative Dopant

“…[34,40] Furthermore, a significant decrease in the intensity of (300) diffraction peak was observed in the doped film which originates from the formation of cocrystals between doped polymers and counter anions. This unique XRD profile suggests that the weighted-center position and number of TFSI − is precisely confined against the repeating unit of PBTTT-C14, [24] which again supports the high doping level estimation from the absorption data. From the 2-terminal conductivity measurement, the doped film exhibited a high electrical conductivity of 656 S cm −1 which is consistent with the result obtained by using TBPA-TFSI.…”

“…The fact that the absorption spectrum of the TAB–2TFSI doped PBTTT–C14 was identical to our previous reports strongly suggests that very high carrier density (close to one hole per monomer unit) was achieved. [ 23,24 ] The impact of the doping process on the microstructure ordering of PBTTT–C14 was also confirmed by X‐ray diffraction (XRD) measurement (Figure 5b,c). A noticeable expansion of lamella stacking and shrinking of π –stacking can be seen from the shift of out‐of‐plane ( h 00) and in‐plane (010) diffraction peaks, respectively.…”

“…Needless to say, the previously reported experimental data describing the doping ability of TBPA-TFSI was obtained from a freshly prepared compound in its solution state where the formation and effect of TAB species are negligible. [24] The disproportionation of TBPA-TFSI was also confirmed by electron spin resonance (ESR) measurement (Figure 2c). The solution ESR signal of the fresh sample showed a nearly identical pattern to TBPA-SbCl 6 (g = 2.00 970) with a g value of 2.00 862 because both compounds share the same TBPA •+ .…”

“…Needless to say, the previously reported experimental data describing the doping ability of TBPA–TFSI was obtained from a freshly prepared compound in its solution state where the formation and effect of TAB species are negligible. [ 24 ]…”

“…By feeding back the notion of the anion exchange doping system, we recently reported a new molecular dopant (tris(4bromophenyl)aminium bis(trifluoromethylsulfonyl)imide; TBPA-TFSI) where the triarylaminium radical cation (TBPA •+ ) serves as the initial doping component and TFSI anion (TFSI − ) to compensate the charges of the doped semiconductor (Figure 1b). [24] As represented by TBPA-SbCl 6 (i.e., tris(4-bromophenyl)aminium hexachloroantimonate), TBPA •+ is known as a persistent radical cation and widely adopted as a strong and clean oxidant. [25][26][27] In addition, TFSI − was chosen as the counter anion because the physicochemical properties, such as binding preference and hydrophobicity of TFSI − significantly contribute to the stabilization of the conducting polymer system.…”