Reduced and Oxidized Forms of the Pt-Organometallic Version of Polyaniline

Abstract

This work represents an effort to synthesize all four forms of polyaniline (PANI) in its organometallic versions. Polymers containing substituted 1,4-benzoquinone diimine or 1,4-diaminobenzene units in the backbone exhibiting the general structure (C≡CC(6)H(4)-N═C(6)X(4)═N-C(6)H(4)C≡C-PtL(2))(n) and (C≡CC(6)H(4)NH-C(6)X(4)-NHC(6)H(4)C≡C-PtL(2))(n) along with the corresponding model compounds (C≡CC(6)H(4)-N═C(6)X(4)═N-C(6)H(4)C≡C)(PtL(2)Cl)(2) and (C≡CC(6)H(4)NH-C(6)X(4)-NHC(6)H(4)C≡C)(PtL(2)Cl)(2) (L = PBu(3); X = H, F, Cl) were synthesized. The polymers and corresponding model compounds were characterized (including (1)H and (31)P NMR, IR, mass spectra, elemental analysis, and X-ray structure determinations) and investigated for their redox properties in the absence and in the presence of acid. Their optical properties, including ns transient spectroscopy were also investigated. These properties were interpreted through density functional theory (DFT) and time-dependent DFT (TDDFT) computations. These materials are found to be oligomers (GPC) with thermal stability (TGA) reaching 350 °C. The greatest stabilities were found in the cases with X = F. Using a data bank of 8 X-ray structures of diimine derivatives, a relationship between the C═N bond distance and the dihedral angle between the benzoquinone ring and the flanking phenyl planes is noted. As the size of the substituent X on the benzoquinone center increases, the degree of conjugation decreases as demonstrated by the C═N bond length. The largest dihedral angles are noted for X = Cl. These polymers exhibit drastic chemical differences when X is varied (X = H, F, Cl). The completely reduced polymer (C≡CC(6)H(4)NH-C(6)H(4)-NHC(6)H(4)C≡C-PtL(2))(n) (i.e., X = H) was not chemically accessible whereas in the cases of X = F, Cl, these materials were obtained and represent the first examples of fully reduced organometallic versions of PANI (i.e., leucoemaraldine). For the (C≡CC(6)H(4)-N═C(6)X(4)═N-C(6)H(4)C≡C-PtL(2))(n) polymers, the completely oxidized form for X = H was isolated (pernigraniline), but for X = F and Cl, only the largely reduced mixed-valence form (i.e., emaraldine) was obtained via chemical routes. In acidic solutions, the chemically accessible polymer for X = H, (C≡CC(6)H(4)-N═C(6)H(4)═N-C(6)H(4)C≡C-PtL(2))(n), exhibits two chemically reversible waves indicating that the reduced form (C≡CC(6)H(4)NH-C(6)H(4)-NHC(6)H(4)C≡C-PtL(2))(n) can be generated. The absorption spectra of the highly colored diimine-containing species exhibit a broad charge transfer band (assigned based on DFT calculations (B3LYP); C(6)H(4)C≡C-PtL(2)-C≡CC(6)H(4) → N═C(6)X(4)═N) in the 450-800 nm window red shifting according X = H → Cl → F, consistent with their relative inductive effect. The largest absorptivity is measured for X = H because this polymer is fully oxidized whereas for the cases where X = F and Cl, these polymers exists in the mixed valence form. The ns transient absorption spectra of two polymers (X = F; reduced and mixed-valence polymers) were measured. The t...

The Pt‐Organometallic Version of Perigraniline: Going Blue

“…However this spectral range is quite unusual and unexpected taking into account previous findings on the benzoquinone diimine systems and the obvious extension of the π‐conjugation in anthraquinone diimine vs benzoquinone diimine (Figure 3). 6–8 Moreover, the UV–vis data indicate that λ max (CT 7b ) > λ max (CT 7a ), which is unusual due to the donating ability of the amino groups, but corroborates somewhat their CV traces. An explanation for these unexpected observations is found in the electrochemistry and X‐ray data below.…”

“…Based on the electron‐donating ability of the amino group, the similarity of the lesser negative reduction peak potentials of 7a and 7b is surprising but corroborates the similarity of the position of their CT band. Concurrently, the reduction peak potentials for the quinone diimine‐containing polymer 1 are +0.51 (anodic) and +0.26 V vs SCE (cathodic sweep) 6. There is clearly a pronounced ease for the latter to be reduced.…”

“… Comparison of the [Pt] *→ AQ CT band position for the anthraquinone diimine‐containing polymers 8a–d with quinone diimine‐containing polymers 1 , 2 , 4–6. 6–8 …”

“…Polyaniline (PANI) is a conducting material that finds applications in batteries and solar cells, notably as a replacement for the ITO (indium/tin oxide) counter electrode, and exists under three forms, perigraniline (fully oxidized; Figure 1), leuco‐emaraldine (fully reduced), and emaraldine (mixed‐valence) 1–5. We recently reported a series of conjugated Pt(II)‐containing quinone diimine polymers ( 1 – 6 ; Figure 1) where every second quinone diimine residue is replaced by a trans ‐PtL 2 (CC) 2 unit hence affording an organometallic version of perigraniline 6–8. These thermally robust materials ( T dec > 300 °C; TGA) are also electroactive but exhibit a characteristic low‐lying charge transfer, CT, band arising from the trans ‐PtL 2 (CCC 6 H 4 ) 2 ( [Pt] ) unit to the quinone diimine center ( Q ) rendering them push–pull systems.…”

Azophenine as Central Core for Efficient Light Harvesting Devices

“…The dihedral angles made by the C 6 H 4 ‐NH‐quinone diimine and by the C 6 H 4 ‐N=quinone diimine, respectively range from ≈30 to 33° and ≈51 to 55°. These ranges are exactly what is expected for this type of steric interactions . The longer single N−C bond with respect to N=C one allows for less steric hindrance between the ortho ‐hydrogens and the central quinone diimine.…”