Supporting Information

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1 Supporting Information Ionic Liquid Designed for PEDOT:PSS Conductivity Enhancement Ambroise de Izarra, a,b,1 Seongjin Park, a,1 Jinhee Lee, a Yves Lansac, b,c, * Yun Hee Jang a, * a Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea; b GREMAN, UMR 7347, CNRS, Université detours, Tours, France c Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Orsay, France lansac@univ-tours.fr, yhjang@dgist.ac.kr. Choice of density functional theory (DFT) functional: Validation. We choose B3LYP in Section 2.1 of the present work to calculate the ion exchange energies because our previous studies have shown a surprisingly good agreement between B3LYP TDDFT calculations and UV/visible absorption spectra of a charge-transfer (donor-acceptor) type of polymers and oligomers. 1-5 However, on the other hand, the current system (PEDOT:PSS, EMIM:X IL, and their combinations) may involve more explicit long-range charge transfer than those donor-acceptor co-polymers. Therefore, our key quantities (binding energy and ion exchange energy) of several key compounds (PEDOT, PSS, EMIM, TCB, and their combinations) calculated with B3LYP are verified with a long-range-corrected or range-separated hybrid functional implemented in Gaussian09, 6 LC- PBE, 7-8 in which the PBE short-range (SR) exchange functional is supplemented by the Hartree- Fock long-range (LR) one, that is, E x (SR-PBE) + E x (LR-HF). After the range separation parameter is tuned (to 0.17 a.u. -1 ) with those key compounds until their ionization potentials and electron affinities are reproduced by their HOMO and LUMO energy levels, respectively, the binding energy (PEDOT:PSS, EMIM:TCB, PEDOT:TCB, EMIM:PSS) and the ion exchange energy (not the free energy; PEDOT:PSS + EMIM:TCB PEDOT:TCB + EMIM:PSS) calculated with the optimized LC- PBE functional are within 4% of error from the B3LYP values as follows. Binding energy (kj/mol) B3LYP LC- PBE ( = 0.17 a.u. -1 ) (kj/mol) (1) PEDOT:PSS (2%) (2) EMIM:TCB (3%) (3) PEDOT:TCB (3%) (4) EMIM:PSS (2%) Exchange energy (kj/mol) B3LYP LC- PBE ( = 0.17 a.u. -1 ) (kj/mol) (3) + (4) (1) (2) (3%) The binding energy of each pair is consistently underestimated by B3LYP (by 6-8 kj/mol or 2-3%). However, such underestimation is rather consistent all over the pairs, and therefore the ion exchange energy obtained from their combination gives 1 kj/mol (3%) of error between LC- PBE (-31 kj/mol) and B3LYP (-32 kj/mol). Therefore, we use B3LYP for the rest of the calculation performed in Section 2.1 of this work.

2 S2. DFT-optimized PEDOT:X binding geometry: Validation. Our minimal model, one single-chain trimer of PEDOT (tri-edot) and a single anion X, used in the DFT geometry optimization should describe well the local pairwise electrostatic interaction between charge groups involved in the IL-triggered PEDOT-PSS separation process and would provide a good framework to estimate the intrinsic feasibility of this process with merits of fast screening and minimum uncertainty in model geometry (conformation/configuration). However, on the other hand, the absence of - stacking in this single tri-edot model could be unrealistic for PEDOT:X (especially PEDOT:TCB) solutions and films and may lead to incorrect binding geometry (as well as binding energy) between PEDOT and X. Therefore, we perform 60-ns molecular dynamics (MD) simulations on PEDOT:PSS models which are similar to (but smaller than) the one used in the work of Franco-Gonzalez and Zozoulenko: 9 a periodic unit cell (6 nm on each side) composed of 12 tri-edot and 12 PTS (Tos) units mixed with ~6500 water molecules. Indeed, 3-to-5-membered small -stacked tri-edot clusters bound with a few PTS anions spontaneously form and stay dispersed in water until the end of the simulation. Adding 12 or 24 EMIM:TCB pairs to this final state induces spontaneous ion exchange and forms a single large cluster of -stacked tri-edot surrounded by TCB anions (Figure, middle and right). The binding geometry found in this domain, in which the anions are also bound to tri-edot mostly from the side, is consistent with the DFT-optimized geometry (Figure, left). On the other hand, the PTS/ES binding geometry from DFT (negatively-charged sulfonates directed toward positivelycharged tri-edot on the side) is not captured by our aqueous-phase MD simulation (hydrophilic sulfonates solvated in water) but rather consistent with the binding configuration of solutioncasted/vapor-phase-polymerized PEDOT:Tos crystals Figure. A cluster of 12 tri-edot units (blue) decorated by TCB anions (red) zoomed in the last snapshot of 60-ns MD simulations on 12 pairs of tri-edot:pts (a minimal model of PEDOT:PSS) mixed with 12 pairs of EMIM:TCB IL in water. Only the most relevant species are shown for clarity. The tri-edot:tcb binding geometries (shown in green boxes) are close to the DFT-optimized geometry (shown on the left).

3 S3. Force field (FF): Energy expressions and parameters. A parametrization of the interaction energy E based on the OPLS-AA FF is used for the MD simulations presented in this work. The functional form is expressed as follows. bonding nonbonding bond angle torsion improper vdw coulomb. Bond stretching (E bond ) Angle bending (E angle ) 2 2 Torsion (E torsion ) Improper torsion (E improper ) 1 1 2

4 Figure S2. Atomic names of tri-edot (1), EMIM (2), ES (3), PTS (4), and TCB (5).

5 Table. FF parameter: Atomic charges taken from our DFT calculations. a Name C1 C2 C3 C4 C5 H6 H7 C8 H9 H10 FF type CA CB CB CA CT HC HC CT HC HC q ( e ) Name C11 C12 C13 C14 C15 H16 H17 C18 H19 H20 FF type CA CB CB CA CT HC HC CT HC HC q ( e ) Name C21 C22 C23 C24 C25 H26 H27 C28 H29 H30 FF type CA CB CB CA CT HC HC CT HC HC q ( e ) Name O31 O32 O33 O34 S35 O36 O37 S38 S39 C40 FF type OS OS OS OS SA OS OS SA SA CT q ( e ) Name H41 H42 H43 C44 H45 H46 H47 C48 C49 N50 FF type HC HC HC CT HC HC HC CA CA N q ( e ) Name N51 C52 C53 C54 C55 H56 H57 H58 H59 H60 FF type N CT CB CT CT HC HC HC HC HC q ( e ) Name H61 H62 H63 H64 H65 H66 S67 O68 O69 O70 FF type HC HC HC HC HC HC SY OY OY OY q ( e ) Name O71 C72 C73 H74 H75 H76 H77 H78 S79 O80 FF type OS CT CT HC HC HC HC HC SY OY q ( e ) Name O81 O82 C83 C84 C85 C86 C87 C88 C89 H90 FF type OY OY CA CA CA CA CA CA CT HA q ( e ) Name H91 H92 H93 H94 H95 H96 B97 C98 C99 C100 FF type HA HA HA HC HC HC BZ CN CN CN q ( e ) Name C101 N102 N103 N104 N105 FF type CN NZ NZ NZ NZ q ( e ) a See Figure S2 for the name of each atom in tri-edot and EMIM:X. Table S2. FF parameter: Lennard-Jones vdw FF type CA CB CT HC OS SA OY N HA BZ (Å) (kcal/mol) FF type CN NZ SY (Å) (kcal/mol)

6 Table S3. FF parameter: Bond stretching Bond type CA-CB CA-CA SA-CA CB-CB OS-CB HC-CT CT-CT OS-CT r0 (Å) Kr (kcal/mol Å 2 ) FF type CT-CA CA-N CT-N CB-N CB-HC CA-HC CA-HA SY-CA r0 (Å) Kr (kcal/mol Å 2 ) FF type SY-OY BZ-CN CN-NZ SY-OS r0 (Å) Kr (kcal/mol Å 2 ) Table S4. FF parameter: Angle bending Angle type CA-CA-CB SA-CA-CB SA-CA-CA CB-CB-CA OS-CB-CA OS-CB-CB o ( ) K (kcal/mol rad 2 ) Angle type HC-CT-HC HC-CT-CT OS-CT-HC OS-CT-CT CT-CA-CB SA-CA-CT o ( ) K (kcal/mol rad 2 ) Angle type CT-OS-CB CA-SA-CA HC-CT-CA N-CA-CA HC-CA-CA N-CA-HC o ( ) K (kcal/mol rad 2 ) Angle type N-CB-HC CA-N-CT CB-N-CA CT-N-CB CT-CT-N N-CT-HC o ( ) K (kcal/mol rad 2 ) Angle type N-CB-N CA-CA-CA HA-CA-CA CT-CA-CA SY-CA-CA CA-SY-OY o ( ) K (kcal/mol rad 2 ) Angle type OY-SY-OY CN-BZ-CN NZ-CN-BZ OY-SY-OS SY-OS-CT o ( ) K (kcal/mol rad 2 )

7 Table S5. FF parameter: Ryckaert-Bellemans dihedral torsion Dihedral type HC-CT-CT-HC HC-CT-CT-OS HC-CT-OS-CB CT-CT-OS-CB CT-OS-CB-CB C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type CT-OS-CB-CA OS-CT-CT-OS *-CB-CA-* *-CB-CB-* CB-CA-CA-SA C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type *-CA-CA-* *-CA-SA-* CB-CB-CA-SA CB-CA-CT-HC CA-CB-CB-CA C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type SA-CA-CA-SA SA-CA-CT-HC *-CT-N-* *-CA-N-* *-CB-N-* C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type N-CA-CA-N *-N-CT-* CB-N-CT-CT CA-N-CT-CT N-CT-CT-HC C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type HC-CT-CA-CA OY-SY-CA-CA NZ-CN-BZ-CN OY-SY-OS-CT SY-OS-CT-HC C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Dihedral type SY-OS-CT-CT OS-CT-CT-HC OS-CT-CT-HC C0 (kcal/mol) C1 (kcal/mol) C2 (kcal/mol) C3 (kcal/mol) Table S6. FF parameter: Improper torsion Torsion type HC-N-CB-N CA-HC-CA-N CT-CB-N-CA f (kcal/mol) o ( )

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