From p‐ to n‐Type Mixed Conduction in Isoindigo‐Based Polymers through Molecular Design

Abstract

dominated by poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and closely related derivatives as the active material, [4][5][6][7] new semiconducting materials have started to enter the arena in recent years. [8][9][10][11][12] In particular, hole-transporting (p-type) mixed conductors have emerged with properties on par or even better than benchmark PEDOT:PSS formulations, [9,13,14] whereas electron-transporting (n-type) materials are still lacking considerably in terms of mixed conduction performance. [15][16][17][18][19] The design of semiconducting materials for bioelectronic applications is heavily influenced by the rich body of literature in the broader field of organic electronics, evidenced by the development of, for example, oligo-and polythiophenes, [8,11,20,21] fullerenes, [18] diketopyrrolopyrrole-, [12,[22][23][24] and naphthalene-diimide-based [15,16] systems as efficient OMIECs. With that in mind, another versatile and highly efficient charge-transporting moiety, isoindigo (IG), has received very little attention for bioelectronic applications. [25] The IG motif depicted in Figure 1a can be structurally modified not only by introducing various solubilizing Organic mixed ionic and electronic conductors are of significant interest for bioelectronic applications. Here, three different isoindigoid building blocks are used to obtain polymeric mixed conductors with vastly different structural and electronic properties which can be further fine-tuned through the choice of comonomer unit. This work shows how careful design of the isoindigoid scaffold can afford highly planar polymer structures with high degrees of electronic delocalization, while subtle structural modifications can control the dominant charge carrier (hole or electron) when probed in organic electrochemical transistors. A combination of experimental and computational techniques is employed to probe electrochemical, structural, and mixed ionic and electronic properties of the polymer series which in turn allows the derivation of important structure-property relations for this promising class of materials in the context of organic bioelectronics. Ultimately, these findings are used to outline robust molecular-design strategies for isoindigo-based mixed conductors that can support efficient p-type, n-type, and ambipolar transistor operation in an aqueous environment.

Cyano‐Functionalized n‐Type Polymer with High Electron Mobility for High‐Performance Organic Electrochemical Transistors

“…The OECT devices of both polymers showed clear n-type accumulation-mode characteristics with almost negligible hysteresis in their transfer and output curves regardless of device gate voltage scan rate (Figures 3a-d, Table 2; with literature-reported channel materials for n-type OECTs; [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] please note the representative high-performance materials based on various electrondeficient building blocks are shown in color with displayed legends while the rest are shown in black.…”

“…Since the pioneering work of p(gNDI-gT2) in 2016, [38] there are only limited number of reports on n-type materials for OECTs (please see summary in Table S1, Supporting Information). They mainly include donor-acceptor (D-A) polymers such as naphthalene diimde (NDI)-based P90, [39,40] p(C6-gNDI-gT2), [41] P(NDIMTEG-T), [42] P(C6-T2), [43] bithiophene diimide-based f-BTI2TEG-FT, [44] isoindigo-based AIG-BT, [45] lactone-based p(C-T), [46] and diketopyrrolopyrrolebased P(gPzDPP-CT2), [47] all-acceptor (A-A) ladder-type polymers BBL [48,49] and PgNaN, [50] small molecule C60-TEG. [51] n-Type organic mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop.…”

“…Their V g -dependent transconductance performances were also shown. e) Comparison of the μC* and μ e,OECT values of f-BTI2g-TVT/f-BTI2g-TVTCN polymerswith literature-reported channel materials for n-type OECTs;[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] please note the representative high-performance materials based on various electrondeficient building blocks are shown in color with displayed legends while the rest are shown in black.…”

Highly Efficient Mixed Conduction in N‐type Fused Small Molecule Semiconductors

“…Notably, different from the charge transport in OFETs, where closer π–π stacking facilities the electron charge transport, [ 29 ] while the charge conduction in OECTs is dominated by the bulk doping as well as ions transport. [ 39 ] We thus postulate that the coexist of face‐on and edge‐on orientation of gNR with its bimodal orientation packing enables effective 3D charge transport, [ 24,40,45,67,68 ] rendering the higher OECT channel mobility up to 10 −2 cm 2 V −1 s −1 than that of hgNR .…”

Solution processable dithioalkylated methylidenyl cyclopentadithiophene based quinoidal small molecules for n-type organic field-effect transistors

“…[31][32][33][34][35] Hence, developing high-performance and ambiently stable n-type OSCs for OFETs is highly desirable. 28,[36][37][38][39][40] In addition, aromatic frameworks with conjugated cores functionalized with electron-withdrawing substituents are suitable building blocks for electron transport. [41][42][43] Among different OSC structural variations, dicyanomethylene (DCN)-substituted quinoidal oligothiophenes are excellent n-type semiconductors because of their high electron affinity originating from the quinoidal structure terminated by two strongly electronwithdrawing groups, affording low-lying LUMO energy levels.…”