Neutral, Ï-Radical-Conjugated Microporous Polymer Films of

Article www.acsanm.org

Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX

Neutral, π‑Radical-Conjugated Microporous Polymer Films of Nanoscale Thickness for Potential Use in Magnetoelectronics and Sensor Devices Venkata Suresh Mothika,*,† Martin Baumgarten,‡ and Ullrich Scherf*,† †

Macromolecular Chemistry Group, Bergische Universität Wuppertal, Gaußstraße 20, 42119 Wuppertal, Germany Max-Planck-Institut Für Polymerforschung, Ackermannweg 10, D-55128 Mainz, Germany

‡

Downloaded via 81.22.46.140 on July 26, 2019 at 10:17:37 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: π-Radical conjugated microporous polymers (CMPs) are highly appealing for optoelectronics, especially optical response-based sensor devices, and their thin film fabrication is demanding for developing functional devices. Toward this, neutral, π-radicalic CMP films (poly-D•, polyT•: SBET-488 m2/g) of nanometer thickness (24, 33 nm) were fabricated from air stable, radicalic carbazole-substituted polychlorotriphenyl methane (PTM) radical monomers using electropolymerization method. Electron paramagnetic resonance spectra with g value of 2.0029 revealed radical nature of monomers, polymer thin films. The monomers in solution and polymer thin films are reversibly reduced electrochemically as observed by cyclic voltammetry measurements. The radicalic CMP films (poly-T•, poly-D•) displayed intervalence charge-transfer (IV-CT) transition at ∼750 nm, which was not observed in their hydrogenated polymer films (poly-TH; SBET-385 m2/g, poly-DH). Poly-T• and poly-D• (both of yellow color) easily undergo a reductive conversion into anionic poly-T− and poly-D− (both of deep blue color) by simply being immersed into a n-Bu4NOH solution. All the properties of thin films are also compared with the chemically synthesized bulk hydrogenated (bulk-poly-TH) and radicalic polymer (bulk-poly-T•) powders. Our results demonstrate the designed synthesis of carbazolic radical monomers and utility of electropolymerization method to achieve π-radical CMP thin films for potential application in magnetoelectronics and sensor devices. KEYWORDS: neutral π-radicals, porous polymers, thin films, electropolymerization π-radicalic CMP material with unique properties based on accelerated host−guest interactions if compared to PTM radical “small” molecules or nonporous conjugated PTM linear analogues, especially for application in sensor devices. Resembling open shell molecules,40,41 π-radicalic CMPs exhibit doublet spin states, which may improve the internal quantum efficiencies of organic light emitting diodes (OLEDs) by avoiding triplet state formation. Nevertheless, preparing such π-radical CMPs in the form of films of controllable nanometer thickness and on conducting electrodes for potential use as active layer of magnetoelectronics and sensor devices is still a challenge. Here, we demonstrate a simple electrochemical approach to fabricate PTM-based, π-radicalic CMP thin films based on metal-free, electrochemical oxidative C−C coupling using carbazole substituted PTM-based radicalic monomers (Scheme 1). Wu et al. and Sheng et al. reported chemically

1. INTRODUCTION Organic radical-containing polymers with weakly interacting unpaired electrons (polyradicals) that are separated by an organic bridge are gaining significant attention recently.1−6 They can show electrochemically reversible reduction− oxidation cycles (redox activity) and fast charging−discharging behavior: promising for applications in electrocatalysis or polymer batteries.7−9 Polychlorotriphenylmethane (PTM) radicals were given preference among the organic radicals studied until date due to their high thermal stability and conveniently approachable synthesis.10,11 The chemistry and physics of PTM based molecules, cages, or self-assembled materials have been studied in molecular switches, as electroluminescence emitters, organic magnets, etc.12−18 Veciana et al. demonstrated distance dependent electron tunneling efficiencies in oligo(para-phenylenevinylene)-(PPV) bridged PTM radicals where the π-conjugated PPV bridge acts as a molecular wire and mediates efficient electron exchange.19−21 Embedding such PTM radical moieties in an extended π-conjugated system22 such as π-conjugated microporous polymers (CMPs)23−39 may result in a multifunctional © XXXX American Chemical Society

Received: April 26, 2019 Accepted: June 27, 2019 Published: June 27, 2019 A

DOI: 10.1021/acsanm.9b00776 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX

Article

ACS Applied Nano Materials

Scheme 1. Generation of π-Radicalic CMP Thin Films from PTM-Based Tricarbazolyl Monomer T• Using Electropolymerization Approach as Well as Reversible Reduction of Monomer Radical T• to Monomer Anion T− and Reversible Reduction of Electropolymerized Polyradicalic CMP Thin Film into Polyanionic Film

DH, poly-D•) linear polymers (12−33 nm thick) on ITO or glassy carbon (GC) electrodes using multisweep cyclic voltammetry (Scheme 1). The radical-containing films were characterized using Fourier transform infrared (FT-IR), UV− vis, and electron paramagnetic resonance (EPR) spectroscopy, etc. Hereby, thickness and roughness are easily controlled by changing the cycle number. EPR spectra confirmed the presence of unpaired electron in the thin films. An electrochemically reversible reduction of PTM radicalic moieties to the corresponding anionic species can be derived from the cyclic voltammogram (CV) curves of the thin films in monomer free solution. Reduction of the radicalic CMP thin films to the corresponding anionic CMPs is also observed after immersion of the films in n-Bu4NOH solutions accompanied by distinct color changes that are observable by the human eye (see images of thin films before and after reduction in Figure 4). Distinct intervalence charge-transfer (IV-CT) phenomena occur between terminal carbazolic moieties and the PTM radical cores in all the radicalic CMP thin films and in the radicalic monomers. Molecular dynamics (MD) simulations further support the ongoing IVCT.

synthesized PTM-based radicalic CMP powders and nanosheets, respectively, made via expensive Pd(0)-catalyzed C−C coupling reaction.7,42 These radical CMPs were prepared in two steps using chemical polymerization of PTM-H monomers followed by treatment with n-Bu4NOH/p-chloranil. A direct one-step chemical synthesis of radical CMPs is not possible due to the high reactivity of the PTM radical center present in the monomers. Moreover, the products need further purification to remove leftover “Pd” impurities. The brominated PTM-H monomers (used by Wu et al.) are not suitable to prepare thin films by electropolymerization. Our proposed electropolymerization approach requires a careful design of monomers consisting of the PTM radical core and electrochemically oxidizable carbazolyl (Cz) moieties on the periphery. In our work, we demonstrate that electrochemical polymerization represents a single step approach to directly achieve high quality thin (nanometer-thin) films of neutral radical CMPs in short time without need for further purification processes. Electropolymerization for fabrication of CMP thin films from carbazole bearing monomers, and their applicability in solution/vapor-phase chemical sensing, organic electronics, solar cells, and electrochemical supercapacitors, was extensively demonstrated by us and others.43−50 Similar approaches can be conveniently applied to prepare also πradicalic CMP thin films with high control over nanometer thickness/roughness so that they are of suitable quality for device fabrication.44,51−53 We used di- and tricarbazolyl substituted PTM-H (DH, TH) and PTM• (D•, T•) monomers, which were easily electropolymerized into thin films of corresponding porous (poly-TH, poly-T•) polymer networks or nonporous (poly-

2. EXPERIMENTAL SECTION 2.1. Materials and Methods. All reagents and chemicals required have been purchased from commercial chemical suppliers, unless stated. 9-(4-Ethynylphenyl)carbazole was purchased from TCI Chemical and Co. Tris[2,3,5,6-tetrachlorobenzene]methane and tri(4-iodo-2,3,5,6-tetrachlorophenyl) methane were synthesized according to the literature procedures.54,55 1H NMR spectra were recorded on Bruker Avance III 400 MHz machine. APCI or FD-MS mass spectra were measured on a Bruker Daltronik microTOF system B


Article


Figure 1. (a) UV−vis absorption spectra of monomers D• and T• in toluene and DMF. (b) Chemical formula representations of radicalic and zwitterionic resonance structures of T• in toluene and DMF, respectively (inset shows daylight images of T• in toluene and DMF). (c) EPR spectra of monomer radicals M•, D•, and T• as powder samples. (KrF*-Laser ATLEX-SI, ATL Wermelskirchen). UV−vis absorption and FT-IR measurements were carried out using JASCO V-670 and FTIR-4200 machines, respectively. Photoluminescence (PL) is measured using a HORIBA Scientific FluoroMax-4 spectrofluorometer connected to a QuantaPhi integrating sphere for determination of PL quantum yields. Bulk polymers of bulk-poly-TH and bulk-polyT• synthesized by the chemical oxidation method were purified by washing with supercritical CO2 in a Tousimis Samdri-795 system. Bulk polymer samples and thin films were activated on a Belprep-vac II at 140 °C and 2 Pa over 12 h for adsorption measurements. Kr and N2 adsorption measurements were carried out using a BEL Japan Inc. Belsorp-max system at 77 K in the relative pressure range of 0− 0.6, and 0−1 (P0 = 1 atm) respectively. Ionization potential measurements were carried out with atmospheric pressure ultraviolet photoelectron spectroscopy System (Riken Keiki AC-2). Thermogravimetric analyses (TGA) were recorded at a Mettler Toledo TGA/ DSC1 STAR machine under Ar atmosphere with a heating rate of 5 °C per min. Atomic force microscopy (AFM) images of the thin films were obtained on a Bruker diInnova system operated in tapping mode, and the surface roughness was extracted from the topography images. 2.2. Electropolymerization. Thin film generation followed similar procedure as reported by our group earlier.56,57 Monomer solutions (0.1 mM) were prepared in dichloromethane (DCM)/ acetonitrile (ACN) (4:1) with 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. A three electrode cell connected to electrochemical workstation PAR VersaSTAT 4 was used under Ar atmosphere at 25 °C. Indium tin oxide (ITO) plates were used as working electrode (WE) combined with Ag°/AgNO3

(0.1 M AgNO3, 0.6 V vs NHE, nonaqueous reference) as reference electrode (RE) and a platinum counter electrode (CE). Potentiodynamic regimes are applied for generating polymer films on the ITO electrodes. The potentiodynamic generation of the films for the AFM measurements involves the application of 5 or 10 cyclic voltammetric cycles between 0 and 1.1 V with a scan rate of 0.1 V s−1. Free-standing thin films required for Kr gas adsorption measurements were prepared by the chronoamperometry method by applying a constant potential of 1.1 V for 20 min followed by a discharging step at 0 V for 60 s to discharge the deposited films. Free standing thin films were delaminated from the electrodes and dried after rinsing with CH3CN, CH2Cl2, and used for Kr adsorption measurements or EPR measurements. The films were activated by annealing at 140 °C prior to the gas adsorption measurements. 2.3. EPR Measurements. The EPR spectra were recorded in an argon-purged toluene as solvent (10−4 M) on a Bruker EMX-plus spectrometer (X-band) equipped with an NMR gauss meter and a variable-temperature control continuous-flow-N2 cryostat (Bruker BVT 2000). 2.4. Theoretical Calculations. Density functional theory (DFT) calculations were performed with hybrid functional B3LYP and 631g(d) basis set. This provided the frontier orbitals as LUMO, SOMO, HOMO, and the spin density distribution of the SOMO. Time dependent DFT (TD-DFT) calculations were performed for the estimate of optical absorption spectra. All calculations were done with Gaussian 09.58 C


Article


Figure 2. Simulated spin density distributions for (a) T•, (b) D•, (c) M• and (d) HOMO, SOMO, and LUMO energy levels for T•.

zwitterionic state16,18 formed by electron transfer from the carbazolyl unit to the PTM radical center since the polar solvent DMF stabilizes the zwitterionic form as shown in Figure 1b. It was noticed that this low-energy, electron-transfer band was bathochromically shifted with increased number of carbazolyl units. The preceding data clearly confirm the electron accepting character of the PTM radical cores. 3.3. EPR Measurements. EPR spectra of monomer radicals provided a broad central line (ΔBpp = 0.29 mT) at g = 2.0029 for the solid powders (Figure 1c); upon diluting the monomer samples in toluene, weak 13C-signals became visible as shoulders with larger sized hyperfine couplings as reported earlier for the parent PTM radical.59,60 For D• and T•, the α-13C coupling constant was estimated to ∼3.1 mT, and for other aromatic 13C, roughly 1.3−1.4 mT were-found, averaging the ortho- and para-13C signals, which slightly differ. Upon degassing and enhancing the resolution, more than one α-13C coupling were observed in the M• and D• samples, and in addition to the ortho- and para-13C signals more lines appear in all cases. After degassing, the diluted toluene solutions under high resolution conditions the differences in the EPR spectra of the monomer samples with one, two, or three carbazolylphenylethynyl substituents (M•, D•, T•) could clearly be resolved (Figure S7). The sharp center signal found for T• with ΔBpp of −0.09 mT, was split into two lines in the case of D• with one single proton in a para-position yielding a hyperfine coupling of AH = 0.165 mT and into three lines for M• due to hyperfine coupling with two protons in parapositions (AH = 0.17 mT). 3.4. Theoretical Calculations. Theoretical calculations suggested nonplanar conformations to all radical monomers (Figure S8). Density functional theory calculations were performed to access the energy of the frontier orbitals and the spin density distribution in the three radical monomers. As anticipated, the highest spin density was localized in the PTM core with only minor spin densities reaching out to the carbazole nitrogens (Figure 2a−c and Table S1). The calculations of the optical absorptions by TD-DFT resulted in prediction of longest wavelength transitions (β-HOMO to

3. RESULTS AND DISCUSSION 3.1. Monomer Radical Synthesis. The PTM building blocks MH, DH, and TH (Schemes S1 and S2) were synthesized through Sonogashira C−C coupling from the corresponding iodo and ethynyl derivatives (see Supporting Information for details). All the PTM radicals M•, D•, and T• were prepared by deprotonation of MH, DH, and TH, respectively, using n-Bu4NOH followed by oxidation using pchloranil. All monomer radicals were purified using chromatographic techniques as dark green solids with good yields of ∼70% and their structural integrity confirmed by MS (see Supporting Information for details). The monomer radical compounds (M•, D•, T•) did not show resolved NMR spectra due to their paramagnetic nature. The radical monomers are stable in the solid state under ambient conditions and also as solutions in common organic solvents. 3.2. Optical Properties. UV−vis absorption spectra of MH, DH, and TH in hexane displayed two main absorption bands at 290 and 365 nm assignable to π−π* transitions of the 9-(4-ethynylphenyl)carbazole chromophore, similar spectra are observed in other organic solvents (Figures S1−S3). Along with these bands at 290/370 nm, the UV−vis spectra of the radical monomers in hexane showed a strong additional band at around 450 nm that was bathochromically shifted and of increased intensity with increased number of carbazolyl substituents (Figures S4−S6). This was assigned to π−π* transitions associated with the PTM radical moiety. All monomer radicals showed an additional weak charge- transfer band in the range of 500−800 nm that was associated with the intervalence charge transfer (IV-CT) between carbazolyl donor and PTM radical acceptor moieties. A slight bathochromic shift in these bands observed with change in the solvent polarity suggested a partial IV-CT. Monomer radicals showed a golden yellow color in common organic solvents, interestingly, in dimethylformamide (DMF) the solution color found to be deep blue and new absorption bands at 492, 572 nm (for M•); 527, 615 nm (for D•); 610 nm (for T•) were observed with complete disappearance of the band around 450 nm (Figure 1a,b). This suggested the formation of a charge-separated, D


Article


Figure 3. First 10 consecutive cyclic voltammograms (CVs) of 0.1 mM solutions of the monomeric radicals T• and D• and their hydrogenated counterparts TH and DH in DCM/acetonitrile (4:1) containing 0.1 M TBAP, GC electrode, potential range −0.6 to 1.1 V, representing growth of (a) poly-T•, (b) poly-TH, (c) poly-D•, and (d) poly-DH thin films. Arrows indicate reversible reduction of PTM radical units in the polymers and * indicates charge trapping-associated peaks. The peak potentials are indicated above the corresponding peaks.

β-SOMO transition) at a λmax of 722 nm, 732 nm, and 716 nm in gas phase and 734 nm, 817 nm, and 740 nm in toluene for T•, D•, and M•, respectively (Figures 2d, S9, and S10; Table S1). 3.5. Electropolymerization. PTM radicals can be reversibly electrochemically reduced to PTM-carbanions at low potentials (−0.2 V vs Ag°/AgCl), while the oxidation occurs at very high potentials (1.6 V).61 Monomer radicals (M•, D•, T•) showed single redox waves at −0.4 V, −0.35 V, −0.3 V, which correspond to the reversible reduction of PTM radicals in accordance with literature reports (Figure S11). It should be noted that the reduction potential was gradually lowered from M• to T• due to increased size of the conjugated system. Irreversible oxidation waves were observed at 1.15 V, 1.10 V, and 1.05 V for M•, D•, and T•, respectively, and were assigned to the oxidation of the electron-rich carbazolyl unit in the monomers. Increase of the size of the conjugated π-system lowered the oxidation potential of the monomers. On the other hand, the hydrogenated monomers MH, DH, TH only showed oxidation peaks at 1.15 V, 1.10 V, and 1.05 V, respectively, corresponding to the oxidation of carbazolyl units (Figure S11). Electropolymerization of tri and tetracarbazolyl-substituted rigid monomers (so-called tectons) into threedimensional conjugated microporous polymer thin films with proper control over thickness and roughness as well as their applications in sensor devices were recently reviewed by our group.44,46 Similar techniques were now used to generate πconjugated radicalic CMP thin films using the monomer radicals D• and T•. Electro-oxidative polymerization of monomer radicals was carried out in a three electrode electrochemical cell with glassy carbon (GC) or indium tin oxide (ITO) working electrodes, a Pt wire counter electrode and Ag°/AgNO3 (0.6 V vs NHE) as nonaqueous reference electrode by polymerizing monomer solution (0.1 mM) in dichloromethane (DCM)/acetonitrile (ACN) (4:1) with 0.1

M tetrabutylammonium perchlorate (TBAP) supporting electrolyte. Multicycle CV of T• in the potential range of −0.7 to 1.1 V resulted in a uniform growth of the π-conjugated radicalic CMP thin film (poly-T•) at the electrodes, as shown in Figure 3a. In first positive scan, a peak potential at 1.05 V corresponding to the oxidation of carbazolyl moiety of T• was observed accompanied by reduction peaks at 0.77 and 0.93 V during the following negative scan representing the reduction of dicarbazole units that are formed in the electrochemical coupling of T•. In the subsequent cycles, the rising oxidative peak at 0.8 V corresponded to the oxidation of an increasing number of dicarbazole links of the poly-T• film, which were subsequently reduced in the reverse scans and represented oxidation/reduction (or charging/discharging) of poly-T•. Progressive rise in peak current with every repeated cycle indicated steadily growth of the polymer on the electrode surface (Figure 3a). Remarkably, reversible reduction of the PTM radical cores of poly-T• was also observed at −0.3 V in the negative potential region and its peak current gradually increased as the cycle number increased. This clearly signifies the increased number of radical centers during electropolymerization into a network of three-dimensionally distributed radicals in the thin film. Low intensity signals at 0.6 V in the positive sweep and −0.2 V in the negative sweep region may be attributed to some charge (cations/anions) trapping during doping/dedoping of poly-T• resulting in an incomplete discharging process (Figure 3a). Interestingly, no such signals of charge trapping were observed when the voltammograms were collected in the potential range from 0 to 1.1 V (Figure S12). Electrochemical generation of poly-TH was also performed using DCM/ACN (4:1) solution of TH (0.1 mM) with TBAP supporting electrolyte using GC working electrode. The first oxidative cycle exhibited a single oxidation peak at 1.05 V corresponding to carbazolyl oxidation, and in the negative scan the reduction of the newly formed E


Article


Figure 4. (a) Kr adsorption isotherms of poly-TH (black), poly-T• (green), poly-DH (blue), and poly-D• (red). (b) N2 adsorption isotherms of bulk-poly-T• (blue) and bulk-poly-TH (green). (c) EPR spectra of poly-T•(blue) and poly-D• (black) thin films (the inset shows photographs of free-standing thin films of (I) poly-T•, (II) poly-D• dispersed in DCM); Normalized UV−vis absorption spectra of (d) poly-DH, poly-TH, and (e) poly-T•, poly-T−, (f) poly-D•, poly-D− thin films before and after immersing poly-T• or poly-D• films with n-Bu4NOH in methanol (the inset shows photographs of thin film-coated ITO electrodes). The absorption wavelengths of corresponding peaks are indicated above the bands.

observed for poly-DH, poly-D•, poly-TH, poly-T•. A new band around 800 cm−1 appeared for all polymer thin films and correspond to C−H bending vibrations of 3/6-substituted carbazoles (absent in monomers) thereby signifying the formation of C−C linkages between the carbazole moieties in 3/6-positions (Figures S17 and S18). The poly-D• and poly-T• polymer thin films possess neutral polychlorotriphenylmethane radical (paramagnetic) centers throughout the polymer network. Therefore, the solid-state NMR spectra of these radicalic polymers will not show resolved NMR signals. On the other hand, polymer films obtained through electropolymerization technique are normally in “mg” scale, which makes it difficult to study them by solid state NMR. All electrogenerated polymer thin films are uniformly grown at the electrode (ITO) surfaces as seen from atomic force microscopy (AFM) images (Figure S19). The calculated thicknesses from the topography images are 24/33 nm and 29/ 12 nm with an average roughness of 8.8/7.0 nm and 7.4/2.4 nm for poly-D•/poly-T• and poly-DH/poly-TH, respectively, representing a moderate surface roughness. However, altering the electrochemical deposition parameters these values can be tuned down to lower roughness values that are preferred for device fabrication.51−53 3.6. Microporosity. The occurrence of a permanent microporosity is characteristic property of CMP networks made from rigid tectons. Electrogenerated, microporous thin films are generally studied using Kr gas adsorption since they are accessible in only small amounts of several milligrams. Kr gas is preferred over N2 for adsorption measurements mainly due to its low saturation pressure (1.63 Torr at 77K).62 This helps to determine pressure changes with higher precision even for low amounts of material such as thin films. Free-standing thin films for sorption studies (determination of BET surface

dicarbazole units was observed at 0.75/0.95 V. In the subsequent cycles, an oxidation peak at 0.78 V (corresponding to dicarbazole oxidation in the poly-TH film) was observed. The progressively increasing peak current with increasing cycle number again suggested progressive film formation (Figure 3b). No reduction signals at −0.3 V (characteristic for PTM radical reduction) were observed for poly-TH during electropolymerization. These results illustrate that growth and formation of poly-T• and poly-TH thin films takes place in similar manner, independent if polyradicals (in poly-T•) are formed or not (in poly-TH). In both cases (triangular rigid monomers T• and TH), the oxidative C−C coupling leads to the formation of three-dimensional networks poly-T• and poly-TH that are expected to be microporous (Figure S13). Similar CV features are observed during the electrochemical generation of poly-D• and poly-DH (Figures 3c,d and S12). Please note that the monomers D• and DH are bifunctional; therefore, the deposited polymer thin films should consist of entangled linear polymer chains in a, possibly nonporous arrangement (Figure S14). As anticipated, applying oxidation potential of 1.1 V, also over multiple cycles, to the monofunctional monomer M• showed no polymer growth. However, a reversible reduction of the PTM radicals was observed at −0.4 V with constant peak current value (Figure S15). All deposited polymer thin films show a reversible charging/discharging in monomer free solutions as well as a linear relationship between peak current (ip) and scan rate (ν), thus indicating the formation of an electroactive polymer on the electrode (Figure S16). Formation of C−C linkages between two carbazolyls is evident from Fourier-transform infrared spectroscopy (FT-IR): A band around 745 cm−1 corresponding to the C−H bending vibration of N-substituted carbazoles is present in DH, D•, TH, T•; and a similar band is F


Article


quite difficult to measure the film samples that are still deposited on ITO substrates: they just provided a weak center line with g of −2.0029 and line width of 0.9 mT. The best spectrum could be measured for free-standing film that had been peeled off from the electrode and transferred into a standard quartz tube: but also for these samples 13C-couplings could not be resolved. Nevertheless, our data clearly confirm the presence of polyradicals in the polymeric thin film of polyD•, poly-T• and bulk-poly-T•. Solid state UV−vis absorption spectra of poly-DH, poly-TH displayed two main absorption bands at 300 and 375 nm assignable to π−π* transitions (Figure 4d). The polyradicalic thin films (poly-D•, poly-T•) show an additional band at around 450 nm that is assigned to π−π* transition associated with the N-carbazolyl-phenylethynyl-substituted PTM radicals (Figure 4e,f). The broad band peaking at around 800 nm may be associated with IV-CT interactions between PTM radicals and bicarbazolyl units with a slight bathochromic shift when going from poly-D• to polyT•. The red-shifted absorption of the polymers if compared to the corresponding monomers should reflect the extension of the π-conjugation. The polyradical thin films show a golden yellow color under day light illumination (Figure 4e/f; inset). When the poly radicalic films were immersed with n-Bu4NOH in methanol for a few minutes, reduction of polyradicals to polyanions was observed. The reduction of structurally similar radicals (incorporated into dimeric small molecules) by nBu4NOH was described by Veciana and co-workers;63 however, the underlying mechanism was not described. We can only conjecture about the underlying mechanism: despite our and the Veciana studies using quite different solvents (methanol or methylene chloride), both the hydroxyl anion OH− of the base and the solvent are most probably involved, for example, in an initial base (OH−) addition step followed by hydrogen transfer from the solvent under formation of water. The process shows some similarity to the acid-induced oxidative doping of conjugated polymers. UV−vis absorption spectra of n-Bu4NOH-treated polymer thin films show new bands at 540 and 620 nm (for poly-D•) and at 615 nm (for poly-T•) with simultaneous disappearance of the 450 nm band (assigned to the PTM radical) accompanied by color changes from golden yellow to strong blue within 2−3 min (Figure 4e,f; inset). Hereby, color and absorption spectra of the n-Bu4NOH treated polymer thin films are similar those of the zwitterionic monomer species in DMF solution. poly-T− and poly-D− are formed both electrochemically (one e− reduction) and chemically (in the presence of methanolic n-Bu4NOH) from poly-T• and poly-D•, respectively. Electrochemical reduction of radicals (poly-T•, poly-D•) to their corresponding anions (poly-T−, poly-D−) is electrochemically completely reversible as seen from the CV curves in monomer free solution (Figure S16). On the other hand, poly-T−, poly-D− (blue in color, Figure 4) formed by chemical reduction are stable under ambient conditions. They may possibly be converted back into the corresponding radical state by treating with mild oxidants such as p-chloranil.

area) and for optical measurements were prepared using the chronoamperometry method. Applying an oxidation potential of 1.1 V for 30 min followed by a discharge potential of 0 V for 30 s delivered free-standing thin films (Figure S20) suitable for porosity measurements. All the polymer thin films were dried at 140 °C under vacuum prior to the sorption measurements. Kr adsorption isotherms of poly-T• and poly-TH as 3D networks (Figure 4a) measured at 77 K until a relative pressure (P/Po) of 0.6 displayed Type-I gas uptake profiles with steep uptake in the low pressure regime as indication for the microporous nature of the polymer thin films with a final gas uptake of 132 and 121 mL/g, respectively. Brunauer-EmmetTeller (BET) model-based fitting of the Kr adsorption isotherms yields surface areas of 488 and 385 m2/g for polyT• and poly-TH, respectively, the corresponding BET fitting parameters and constants are listed in Figure S21. Contrastingly, poly-D• and poly-DH (2D polymers) showed no significant Kr gas uptake at 77 K and are, thus, nonporous in nature. It is interesting to note that, in case of poly-TH, the central carbon of the polychlorotriphenylmethane (PTM) moiety is connected to an H atom probably facing toward the pore surface, while it is a radical center in case of poly-T•. However, although the polymer structure differs in only these H atoms, the effective (available/accessible) pore surface may be significantly reduced, and thus, the amount of Kr adsorbed for poly-TH is decreased if compared to poly-T•. As a result, the surface area for poly-T• is effectively higher than for polyTH (SBET for poly-T• = 488 m2/g ; poly-TH = 385 m2/g). Please note that the monomers D• and DH are bifunctional; therefore, the deposited polymer thin films should consist of entangled linear polymer chains in a possibly nonporous arrangement. As shown in Figure 4a, both poly-D• and polyDH showed no Kr adsorption uptake, hence, pointing to very low surface areas. Porosity properties of poly-T• and poly-TH thin films were compared with the corresponding chemically synthesized bulk networks. Iron(III)chloride oxidation of TH as alternate C−C coupling method was used to prepare bulkpoly-TH at room temperature (see Supporting Information for details). Treating bulk-poly-TH with n-Bu4NOH followed by oxidation with p-chloranil produced the polyradicalic bulk polymer (bulk-poly-T•) as dark solid. As for the electropolymerized products, a new band around 800 cm−1 appeared in FT-IR spectra for both powder bulk polymers and corresponds to C−H bending vibrations of 3/6-substituted carbazoles (absent in TH, T•) as signature for the formation of carbazole-carbazole linkages (Figure S22). Both bulk polymers showed appreciable thermal stability until 250 °C, at temperatures of >250 °C a gradual weight loss of ∼30% is observed until 800 °C (Figures S23 and S24). N2 gas adsorption measurements showed typical Type-I adsorption isotherms for bulk-poly-TH and bulk-poly-T•, respectively, with a steep uptake at low pressures as indication of the microporous nature (Figure 4b). The BET surface areas are calculated to be 483 and 433 m2/g for bulk-poly-TH and bulk-poly-T•, respectively (the BET fitting parameters are listed in Figure S25). Please note that the extracted BET surface area values from Kr gas (thin films) and N2 gas (bulk powders) adsorption measurements are quite comparable thus suggesting similarities in the cross-linking density of both materials. 3.7. EPR and Optical Properties. EPR spectra of electrogenerated thin films (Figure 4c) and powder samples (Figure S26) were also recorded and compared. Hereby, it was

4. CONCLUSIONS We have prepared three air-stable monomeric PTM radicals that are mono-, di-, and tricarbazolyl substituted. All radical monomers possess high spin density at the PTM center. Electrochemical, oxidative C−C coupling of the trifunctional monomer T• produced microporous polyradicalic CMP thin films (also as free-standing films) of moderate roughness and G


Article

ACS Applied Nano Materials controllable nanometer thickness. The π-radicalic monomers and polymer thin films displayed IV-CT transitions (β-HOMO to β-SOMO) occurring from the carbazolyl to the PTM moiety, which are completely absent in hydrogenated monomers and the corresponding polymer films. The polyradicalic thin films showed remarkable conversion to polyanionic species after treatment with n-Bu4NOH in methanol. We believe that these polyradicalic, microporous thin films will initiate further research into possible application scenarios as thin film sensors or as materials for magnetoelectronics/spintronics. Spin−spin interactions in polychlorotriphenyl methane (PTM)-based radicalic small molecules, self-assembled monolayers (SAMs), or self-assembled nanostructures were intensely studied by Veciana et al. and others.1−3,12 We expect a similar behavior for our materials. Such spin−spin interactions (e.g., in poly-T•, poly-D•) will be the focus of further investigation.

■

(7) Wu, S.; Li, M.; Phan, H.; Wang, D.; Herng, T. S.; Ding, J.; Lu, Z.; Wu, J. Toward Two-Dimensional π-Conjugated Covalent Organic Radical Frameworks. Angew. Chem., Int. Ed. 2018, 57, 8007−8011. (8) Wang, S.; Li, F.; Easley, A. D.; Lutkenhaus, J. L. Real-time Insight into the Doping Mechanism of Redox-Active Organic Radical Polymers. Nat. Mater. 2019, 18, 69−75. (9) Xu, F.; Xu, H.; Chen, X.; Wu, D.; Wu, Y.; Liu, H.; Gu, C.; Fu, R.; Jiang, D. Radical Covalent Organic Frameworks: A General Strategy to Immobilize Open-Accessible Polyradicals for High-Performance Capacitive Energy Storage. Angew. Chem., Int. Ed. 2015, 54, 6814− 6818. (10) Armet, O.; Veciana, J.; Rovira, C.; Riera, J.; Castaner, J.; Molins, E.; Rius, J.; Miravitlles, C.; Olivella, S.; Brichfeus, J. Inert Carbon Free Radicals. 8. Polychlorotriphenylmethyl Radicals: Synthesis, Structure, and Spin-Density Distribution. J. Phys. Chem. 1987, 91, 5608−5616. (11) Elsner, O.; Ruiz-Molina, D.; Vidal-Gancedo, J.; Rovira, C.; Veciana, J. Synthesis and Characterization of a Nanoscopic MolecularScale Wire Bearing Terminal Redox-Active Polychlorotriphenylmethyl Radicals. Nano Lett. 2001, 1, 117−120. (12) Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Vaughan, G.; Tejada, J.; Rovira, C.; Veciana, J. A Robust Purely Organic Nanoporous Magnet. Angew. Chem., Int. Ed. 2004, 43, 1828− 1832. (13) Sporer, C.; Ratera, I.; Wurst, K.; Ruiz-Molina, D.; Rovira, C.; Veciana, J. Ferrocene Triphenylmethyl Radical Donor-Acceptor Compounds. Towards Development of Multifunctional Molecular Switches. ARKIVOC 2004, 2005, 104−114. (14) Castellanos, S.; Velasco, D.; López-Calahorra, F.; Brillas, E.; Julia, L. Taking Advantage of the Radical Character of Tris(2,4,6trichlorophenyl)methyl to Synthesize New Paramagnetic Glassy Molecular Materials. J. Org. Chem. 2008, 73, 3759−3767. (15) Souto, M.; Guasch, J.; Lloveras, V.; Mayorga, P.; López Navarrete, J. T.; Casado, J.; Ratera, I.; Rovira, C.; Painelli, A.; Veciana, J. Thermomagnetic Molecular System Based on TTF-PTM Radical: Switching the Spin and Charge Delocalization. J. Phys. Chem. Lett. 2013, 4, 2721−2726. (16) Steeger, M.; Griesbeck, S.; Schmiedel, A.; Holzapfel, M.; Krummenacher, I.; Braunschweig, H.; Lambert, C. On The Relation of Energy and Electron Transfer in Multidimensional Chromophores Based on Polychlorinated Triphenylmethyl Radicals and Triarylamines. Phys. Chem. Chem. Phys. 2015, 17, 11848−11867. (17) Gu, X.; Gopalakrishna, T. Y.; Phan, H.; Ni, Y.; Herng, T. S.; Ding, J.; Wu, J. A Three-Dimensionally π-Conjugated Diradical Molecular Cage. Angew. Chem., Int. Ed. 2017, 56, 15383−15387. (18) Dong, S.; Obolda, A.; Peng, Q.; Zhang, Y.; Marder, S.; Li, F. Multicarbazolyl Substituted TTM Radicals: Red-Shift of Fluorescence Emission with Enhanced Luminescence Efficiency. Mater. Chem. Front. 2017, 1, 2132−2135. (19) Lloveras, V.; Vidal-Gancedo, J.; Figueira-Duarte, T. M.; Nierengarten, J.-F.; Novoa, J. J.; Mota, F.; Ventosa, N.; Rovira, C.; Veciana, J. Tunneling Versus Hopping in Mixed-Valence Oligo-PPhenylenevinylene Polychlorinated Bis(Triphenylmethyl) Radical Anions. J. Am. Chem. Soc. 2011, 133, 5818−5833. (20) Rovira, C.; Ruiz-Molina, D.; Elsner, O.; Vidal-Gancedo, J.; Bonvoisin, J.; Launay, J.-P.; Veciana, J. Influence of Topology on the Long-Range Electron-Transfer Phenomenon. Chem. - Eur. J. 2001, 7, 240−250. (21) Bonvoisin, J.; Launay, J.-P.; Rovira, C.; Veciana, J. Purely Organic Mixed-Valence Molecules with Nanometric Dimensions Showing Long-Range Electron Transfer. Synthesis, and Optical and EPR Studies of a Radical Anion Derived from a Bis(triarylmethyl)Diradical. Angew. Chem., Int. Ed. Engl. 1994, 33, 2106−2109. (22) Nishide, H.; Kaneko, T.; Toriu, S.; Katoh, K.; Takahashi, M.; Tsuchida, E.; Yamaguchi, K. π-Conjugated Polyradicals With Poly(Phenylene-Vinylene) Skeleton and Their Through-Bond and Long-Range Interaction. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 1995, 272, 131−138.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.9b00776.

■

Synthesis, NMR and MS data, UV−vis spectrum, CV measurements, FT-IR spectra, BET parameters, EPR spectra, TGA analysis, AFM images of monomers and polymers (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Venkata Suresh Mothika: 0000-0002-3084-1279 Martin Baumgarten: 0000-0002-9564-4559 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS V.S.M. thanks Alexander von Humboldt foundation for postdoctoral fellowship. V.S.M. thanks Sylwia Adamczyk and Anke Helfer for AFM and MS measurements.

■

REFERENCES

(1) Rajca, A. Organic Diradicals and Polyradicals: From Spin Coupling to Magnetism? Chem. Rev. 1994, 94, 871−893. (2) Nishide, H.; Kaneko, T.; Nii, T.; Katoh, K.; Tsuchida, E.; Yamaguchi, K. Through-Bond and Long-Range Ferromagnetic Spin Alignment in π-Conjugated Polyradical with a Poly(phenylenevinylene) Skeleton. J. Am. Chem. Soc. 1995, 117, 548−549. (3) Nishide, H. High-Spin Alignment in π-Conjugated Polyradicals: A Magnetic Polymer. Adv. Mater. 1995, 7, 937−941. (4) Yan, W.; Wan, X.; Xu, Y.; Lv, X.; Chen, Y. A Phenalenyl-based Neutral Stable π-Conjugated Polyradical. Synth. Met. 2009, 159, 1772−1777. (5) Reta, D.; Moreira, I. d. P. R.; Illas, F. Calix[n]arene-based Polyradicals: Enhancing Ferromagnetism by Avoiding Edge Effects. Phys. Chem. Chem. Phys. 2017, 19, 24264−24270. (6) Wu, Y.; Han, J.-M.; Hong, M.; Krzyaniak, M. D.; Blackburn, A. K.; Fernando, I. R.; Cao, D. D.; Wasielewski, M. R.; Stoddart, J. F. XShaped Oligomeric Pyromellitimide Polyradicals. J. Am. Chem. Soc. 2018, 140, 515−523. H


Article

ACS Applied Nano Materials (23) Chaoui, N.; Trunk, M.; Dawson, R.; Schmidt, J.; Thomas, A. Trends and Challenges for Microporous Polymers. Chem. Soc. Rev. 2017, 46, 3302−3321. (24) Li, X.-C.; Zhang, Y.; Wang, C.-Y.; Wan, Y.; Lai, W.-Y.; Pang, H.; Huang, W. Redox-Active Triazatruxene-Based Conjugated Microporous Polymers for High-Performance Supercapacitors. Chem. Sci. 2017, 8, 2959−2965. (25) Pallavi, P.; Bandyopadhyay, S.; Louis, J.; Deshmukh, A.; Patra, A. A Soluble Conjugated Porous Organic Polymer: Efficient White Light Emission in Solution, Nanoparticles, Gel and Transparent Thin Film. Chem. Commun. (Cambridge, U. K.) 2017, 53, 1257−1260. (26) Sun, C.-J.; Zhao, X.-Q.; Wang, P.-F.; Wang, H.; Han, B.-H. Thiophene-Based Conjugated Microporous Polymers: Synthesis, Characterization and Efficient Gas Storage. Sci. China: Chem. 2017, 60, 1067−1074. (27) Bonillo, B.; Sprick, R. S.; Cooper, A. I. Tuning Photophysical Properties in Conjugated Microporous Polymers by Comonomer Doping Strategies. Chem. Mater. 2016, 28, 3469−3480. (28) Pan, L.; Xu, M.-Y.; Feng, L.-J.; Chen, Q.; He, Y.-J.; Han, B.-H. Conjugated Microporous Polycarbazole Containing Tris(2Phenylpyridine)Iridium(III) Complexes: Phosphorescence, Porosity, and Heterogeneous Organic Photocatalysis. Polym. Chem. 2016, 7, 2299−2307. (29) Suresh, V. M.; Bandyopadhyay, A.; Roy, S.; Pati, S. K.; Maji, T. K. Highly Luminescent Microporous Organic Polymer With Lewis Acidic Boron Sites on the Pore Surface: Ratiometric Sensing and Capture of F− Ions. Chem. - Eur. J. 2015, 21, 10799−10804. (30) Bildirir, H.; Paraknowitsch, J. P.; Thomas, A. A Tetrathiafulvalene (TTF)-Conjugated Microporous Polymer Network. Chem. - Eur. J. 2014, 20, 9543−9548. (31) Suresh, V. M.; Bonakala, S.; Roy, S.; Balasubramanian, S.; Maji, T. K. Synthesis, Characterization, and Modeling of a Functional Conjugated Microporous Polymer: CO2 Storage and Light-Harvesting. J. Phys. Chem. C 2014, 118, 24369−24376. (32) Fischer, S.; Schmidt, J.; Strauch, P.; Thomas, A. An Anionic Microporous Polymer Network Prepared by the Polymerization of Weakly Coordinating Anions. Angew. Chem., Int. Ed. 2013, 52, 12174−12178. (33) Xu, Y.; Jin, S.; Xu, H.; Nagai, A.; Jiang, D. Conjugated Microporous Polymers: Design, Synthesis and Application. Chem. Soc. Rev. 2013, 42, 8012−8031. (34) Vilela, F.; Zhang, K.; Antonietti, M. Conjugated Porous Polymers for Energy Applications. Energy Environ. Sci. 2012, 5, 7819. (35) Patra, A.; Scherf, U. Fluorescent Microporous Organic Polymers: Potential Testbed for Optical Applications. Chem. - Eur. J. 2012, 18, 10074−10080. (36) Li, A.; Lu, R.-F.; Wang, Y.; Wang, X.; Han, K.-L.; Deng, W.-Q. Lithium-Doped Conjugated Microporous Polymers for Reversible Hydrogen Storage. Angew. Chem., Int. Ed. 2010, 49, 3330−3333. (37) Yuan, K.; Hu, T.; Xu, Y.; Graf, R.; Shi, L.; Forster, M.; Pichler, T.; Riedl, T.; Chen, Y.; Scherf, U. Nitrogen-Doped Porous Carbon/ Graphene Nanosheets Derived From Two-Dimensional Conjugated Microporous Polymer Sandwiches With Promising Capacitive Performance. Mater. Chem. Front. 2017, 1, 278−285. (38) Yuan, K.; Guo-Wang, P.; Hu, T.; Shi, L.; Zeng, R.; Forster, M.; Pichler, T.; Chen, Y.; Scherf, U. Nanofibrous and GrapheneTemplated Conjugated Microporous Polymer Materials for Flexible Chemosensors and Supercapacitors. Chem. Mater. 2015, 27, 7403− 7411. (39) Yuan, K.; Zhuang, X.; Fu, H.; Brunklaus, G.; Forster, M.; Chen, Y.; Feng, X.; Scherf, U. Two-Dimensional Core-Shelled Porous Hybrids as Highly Efficient Catalysts for the Oxygen Reduction Reaction. Angew. Chem., Int. Ed. 2016, 55, 6858−6863. (40) Peng, Q.; Obolda, A.; Zhang, M.; Li, F. Organic Light-Emitting Diodes Using a Neutral π Radical as Emitter: The Emission from a Doublet. Angew. Chem., Int. Ed. 2015, 54, 7091−7095. (41) Mukherjee, S.; Boudouris, B. W. Organic Radical Polymers: New Avenues in Organic Electronics; Springer International Publishing, 2017.

(42) Yang, Y.; Liu, C.; Xu, X.; Meng, Z.; Tong, W.; Ma, Z.; Zhou, C.; Sun, Y.; Sheng, Z. Antiferromagnetism in Two-Dimensional Polyradical Nanosheets. Polym. Chem. 2018, 9, 5499−5503. (43) Mothika, V. S.; Räupke, A.; Brinkmann, K. O.; Riedl, T.; Brunklaus, G.; Scherf, U. Nanometer-Thick Conjugated Microporous Polymer Films for Selective and Sensitive Vapor-Phase TNT Detection. ACS Appl. Nano Mater. 2018, 1, 6483−6492. (44) Suresh, V. M.; Scherf, U. Electrochemically Generated Conjugated Microporous Polymer Network Thin Films for Chemical Sensor Applications. Macromol. Chem. Phys. 2018, 219, 1800207. (45) Gu, C.; Huang, N.; Chen, Y.; Zhang, H.; Zhang, S.; Li, F.; Ma, Y.; Jiang, D. Porous Organic Polymer Films with Tunable Work Functions and Selective Hole and Electron Flows for Energy Conversions. Angew. Chem., Int. Ed. 2016, 55, 3049−3053. (46) Palma-Cando, A.; Scherf, U. Electrochemically Generated Thin Films of Microporous Polymer Networks: Synthesis, Properties, and Applications. Macromol. Chem. Phys. 2016, 217, 827−841. (47) Gu, C.; Huang, N.; Chen, Y.; Qin, L.; Xu, H.; Zhang, S.; Li, F.; Ma, Y.; Jiang, D. π-Conjugated Microporous Polymer Films: Designed Synthesis, Conducting Properties, and Photoenergy Conversions. Angew. Chem., Int. Ed. 2015, 54, 13594−13598. (48) Zhang, H.; Zhang, Y.; Gu, C.; Ma, Y. Electropolymerized Conjugated Microporous Poly(zinc-porphyrin) Films as Potential Electrode Materials in Supercapacitors. Adv. Energy Mater. 2015, 5, 1402175. (49) Gu, C.; Huang, N.; Gao, J.; Xu, F.; Xu, Y.; Jiang, D. Controlled Synthesis of Conjugated Microporous Polymer Films: Versatile Platforms for Highly Sensitive and Label-Free Chemo- and Biosensing. Angew. Chem., Int. Ed. 2014, 53, 4850−4855. (50) Gu, C.; Chen, Y.; Zhang, Z.; Xue, S.; Sun, S.; Zhang, K.; Zhong, C.; Zhang, H.; Pan, Y.; Lv, Y.; Yang, Y.; Li, F.; Zhang, S.; Huang, F.; Ma, Y. Electrochemical Route to Fabricate Film-Like Conjugated Microporous Polymers and Application for Organic Electronics. Adv. Mater. 2013, 25, 3443−3448. (51) Heinze, J.; Frontana-Uribe, B. A.; Ludwigs, S. Electrochemistry of Conducting Polymers–Persistent Models and New Concepts. Chem. Rev. 2010, 110, 4724−4771. (52) Koyuncu, S.; Gultekin, B.; Zafer, C.; Bilgili, H.; Can, M.; Demic, S.; Kaya, I.;̇ Icli, S. Electrochemical and Optical Properties of Biphenyl Bridged-Dicarbazole Oligomer Films: Electropolymerization and Electrochromism. Electrochim. Acta 2009, 54, 5694−5702. (53) Ambrose, J. F.; Nelson, R. F. Anodic Oxidation Pathways of Carbazoles. J. Electrochem. Soc. 1968, 115, 1159. (54) Ballester, M.; Riera, J.; Castañer, J.; Rovira, C.; Armet, O. An Easy, High-yield Synthesis of Highly Chlorinated Mono-, Di- and Triarylmethanes. Synthesis 1986, 1986, 64−66. (55) Wu, X.; Kim, J. O.; Medina, S.; Ramírez, F. J.; Mayorga Burrezo, P.; Wu, S.; Lim, Z. L.; Lambert, C.; Casado, J.; Kim, D.; et al. Push-Pull-Type Polychlorotriphenylmethyl Radicals: New TwoPhoton Absorbers and Dyes for Generation of Photo-Charges. Chem. - Eur. J. 2017, 23, 7698−7702. (56) Palma-Cando, A.; Woitassek, D.; Brunklaus, G.; Scherf, U. Luminescent Tetraphenylethene-Cored, Carbazole- and ThiopheneBased Microporous Polymer Films for The Chemosensing of Nitroaromatic Analytes. Mater. Chem. Front. 2017, 1, 1118−1124. (57) Mothika, V. S.; Räupke, A.; Brinkmann, K. O.; Riedl, T.; Brunklaus, G.; Scherf, U. Nanometer-Thick Conjugated Microporous Polymer Films for Selective and Sensitive Vapor-Phase TNT Detection. ACS Appl. Nano Mater. 2018, 1, 6483−6492. (58) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, I


Article

ACS Applied Nano Materials J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.: Wallingford, CT, 2009. (59) Ballester, M.; Riera-Figueras, J.; Castaner, J.; Badfa, C.; Monso, J. M. Inert Carbon Free Radicals. I. Perchlorodiphenylmethyl and Perchlorotriphenylmethyl Radical Series. J. Am. Chem. Soc. 1971, 93, 2215−2225. (60) Falle, H. R.; Luckhurst, G. R.; Horsfield, A.; Ballester, M. Electron Resonance Studies of Perchlorodiphenylmethyl and Perchlorotriphenylmethyl Free Radicals. J. Chem. Phys. 1969, 50, 258−264. (61) Souto, M.; Rovira, C.; Ratera, I.; Veciana, J. TTF−PTM Dyads: From Switched Molecular Self-Assembly in Solution to Radical Conductors in Solid State. CrystEngComm 2017, 19, 197−206. (62) Pauporté, T.; Rathouský, J. Electrodeposited Mesoporous ZnO Thin Films as Efficient Photocatalysts for the Degradation of Dye Pollutants. J. Phys. Chem. C 2007, 111, 7639−7644. (63) Franco, C.; Burrezo, P. M.; Lloveras, V.; Caballero, R.; Alcón, I.; Bromley, S. T.; Mas-Torrent, M.; Langa, F.; López Navarrete, J. T.; Rovira, C.; Casado, J.; Veciana, J. Operative Mechanism of HoleAssisted Negative Charge Motion in Ground States of Radical-Anion Molecular Wires. J. Am. Chem. Soc. 2017, 139, 686−692.

J


Neutral, Ï-Radical-Conjugated Microporous Polymer Films of

Recommend Documents

Neutral, Ï-Radical-Conjugated Microporous Polymer Films of