Stable Radical Isoporphyrin Copolymer Prepared with Di(phenylphosphane)

Abstract

Two diphosphanes with variable-length ligands tested as nucleophiles to prepare isoporphyrin copolymers in the presence of ditolylporphyrin of zinc (ZnT₂P) prevented the oxidation of the diphosphine ligand. This paper demonstrates the power of this approach and describes the photoelectrocatalytic properties. The obtained copolymers were characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy, atomic force micrograph (AFM), EQCM (Electrochemical Quartz Cristal Microbalance) and electrochemistry. Their impedance properties (EIS) were studied and their photovoltaic performances were also investigated by photocurrent transient measurements under visible light irradiation.

Keywords: EPR spectroscopy; EQCM; electrochemistry; phosphonium; photocurrent; porphyrin.

Scheme 1

Representation of the zinc-tetraphenylporphyrin (ZnTPP), zinc-meso-5,15-ditolyl-porphyrin (ZnT₂P), cis-1,2-bis(diphenylphosphino)ethene (1), and 1,2-bis(diphenylphosphino)benzene (2).

Scheme 2

Representation of electropolymerization reaction from zinc-meso-5,15-ditolyl-porphyrin (ZnT₂P), cis-1,2-bis-(diphenyl-phosphino)ethene (1), and 1,2-bis-(diphenylphosphino)-benzene (2).

Figure 1

(A) Cyclic voltammograms recorded of cis-1,2-bis(diphenylphosphino)ethene and 1,2-bis(diphenylphosphino)benzene in CH₃CN/1,2-C₂H₄Cl₂ (3/7) with 0.1 mmol·L⁻¹ NBu₄PF₆, v = 0.1 V·s⁻¹. Cyclic voltammograms recorded during 25 iterative scans conducted between −1.1 V and +1.0 V vs. SCE in the presence of ZnT₂P (0.25 mmol·L⁻¹) with (B) cis-1,2-bis(diphenylphosphino)ethene (0.25 mmol·L⁻¹) and (C) 1,2-bis(diphenylphosphino)benzene (0.25 mmol·L⁻¹) in a 1,2-C₂H₄Cl₂/CH₃CN (7/3) solution with NBu₄PF₆ (0.1 mol·L⁻¹). WE: ITO. S = 1 cm². v = 0.1 V·s⁻¹. Blue curve: first scan (n = 1). Red curve: final scan (n = 25).

Figure 2

(A) Electrochemical quartz crystal microbalance measurements (Δm) and consecutive cyclic voltammograms (first 25 scans) of poly-ZnT₂isoP2 and 1,2-bis(diphenylphosphino)benzene ligand. (B) Mass change (Δm) of the first 25 scans calculated from Sauerbrey’s equation versus the number of scan n of poly-ZnT₂isoP2. (C) Proposed redox reactivity of poly-ZnT₂isoP2. (D) Figure of poly-ZnT₂isoP2 copolymer films deposited at 25 scans between −1.0 V and 1.0 V (v = 100 mV·s⁻¹) on the ITO and after oxidized to 1.6 V on the ITO.

Figure 3

(A) Repeat unit are (isoZnT₂P-⁺PPh₂-HC=CH-PPh₂⁺·2PF₆⁻) and (isoZnT₂P-⁺PPh₂-Ph-PPh₂⁺·2PF₆⁻) for poly-ZnT₂isoP1 and poly-ZnT₂isoP2, respectively. (B) The mass change calculated from Faraday’s law (Δm_calc = MQ/(nFA), where M is the molecular mass of the repeat unit, Q is the anodic charge measured from CV, n the number of electrons exchanged, 3 electrons and is the surface of the electrode) and compared with Δm_EQCM measured from EQCM data vs. the iterative scan numbers n (n = 3, 5, 10 and 20).

Figure 4

XPS spectra of the modified ITO electrodes with poly-ZnT₂isoP2 obtained after 25 iterative scans between −1.1 V and 1.0 V versus SCE. XPS spectra (A), P 2p (B), C 1s (C), N 1s (D).

Figure 5

X-Band EPR spectrum in DMF of poly-ZnT₂isoP1 and poly-ZnT₂isoP2 at room temperature. The solution of copolymer was prepared by washing with 160 mL of DMF the covered ITO obtained using 25 scans between 1.1 V and +1.0 V versus SCE and -, v = 100 mV·s⁻¹. In order to have enough solution, the operation was repeated three times.

Figure 6

(A) UV–vis–NIR spectra of poly-ZnT₂isoP1 and of poly-ZnT₂isoP2. (B) Cyclic voltammograms recorded for poly-ZnT₂isoP1 and poly-ZnT₂isoP2. (C) Photoelectrochemical response. (D) ESI Nyquist of poly-ZnT₂isoP1 after 20 iterative scans and of poly-ZnT₂isoP2 for the film obtained after 10 iterative scans.

Figure 7

Tapping mode AFM topography of (A,C) of poly-ZnT₂isoP1 and poly-ZnT₂isoP2, respectively. (B,D) Section analysis of the coils marked by a white line of poly-ZnT₂isoP1 and poly-ZnT₂isoP2, respectively.

Figure 8

(A) The structures of poly-ZnT₂isoP1 and poly-ZnT₂isoP2. (B,C) Schematic illustrations of the energy level diagram for poly-ZnT₂isoP1 showing electron transfer processes in H₂O containing I₃⁻ 5 mmol·L⁻¹ and I⁻ 0.5 mol·L⁻¹ (-(Ph)₂P⁺- = di(phenylphosphonium); Porp = porphyrin).