Near-Infrared Photoelectrochemical Conversion via Photoinduced Charge Separation in Supramolecular Complexes of Anionic Phthalocyanines with Li<sup>+</sup>@C<inf>60</inf>

Yuki Kawashima, Kei Ohkubo, Vicente Manuel Blas-Ferrando, Hayato Sakai, Enrique Font-Sanchis, Javier Ortíz, Fernando Fernández-Lázaro, Taku Hasobe, Ángela Sastre-Santos, Shunichi Fukuzumi

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Abstract

Two phthalocyanines possessing carboxylate groups ((TBA)<inf>4</inf> H<inf>2</inf> Pc·1 and (TBA)<inf>4</inf> H<inf>2</inf> Pc·2) form 1:2 supramolecular complexes with lithium cation-encapsulated C<inf>60</inf> (Li<sup>+</sup>@C<inf>60</inf> ) [H<inf>2</inf> Pc·1<sup>4-</sup>/(Li<sup>+</sup>@C<inf>60</inf> )<inf>2</inf> and H<inf>2</inf> Pc·2<sup>4-</sup>/(Li<sup>+</sup>@C<inf>60</inf> )<inf>2</inf> ] in a polar mixed solvent. From the UV-vis spectral changes, the binding constants (K) were estimated as ca. 10<sup>12</sup> M<sup>-2</sup>. Upon the photoexcitation of constructed supramolecular complexes, photoinduced electron transfer occurred to form the charge-separated (CS) state. The lifetime of the CS state was determined to be 1.2 ms for H<inf>2</inf> Pc·2<sup>4-</sup>/(Li<sup>+</sup>@C<inf>60</inf> )<inf>2</inf> , which is the longest CS lifetime among the porphyrinoid/fullerene supramolecular complexes. H<inf>2</inf> Pc·1<sup>4-</sup>/(Li<sup>+</sup>@C<inf>60</inf> )<inf>2</inf> also afforded the long-lived CS state of 1.0 ms. The spin state of the long-lived CS states was determined to be a triplet, as indicated by the EPR signal at g = 4. The reorganization energy (λ) and the electronic coupling term were determined to be λ = 1.70 eV, V = 0.15 cm<sup>-1</sup> from the temperature dependence of the rate constant for the charge recombination of the CS state of H<inf>2</inf> Pc·1<sup>4-</sup>/(Li<sup>+</sup>@C<inf>60</inf> )<inf>2</inf> . The energy of the CS state (0.49 eV) is much smaller than the reorganization energy, indicating that the back-electron-transfer process is located in the Marcus normal region. The small electronic coupling term results from the spin-forbidden back electron transfer due to the triplet CS state. Supramolecular complexes of anionic zinc phthalocyanines with Li<sup>+</sup>@C<inf>60</inf> were also prepared and investigated. The ZnPc·4<sup>4-</sup>/Li<sup>+</sup>@C<inf>60</inf> supramolecular nanoclusters were assembled on the optically transparent electrode (OTE) of nanostructured SnO<inf>2</inf> (OTE/SnO<inf>2</inf> ) to construct the dye-sensitized solar cell. The IPCE (incident photon-to-photocurrent efficiency) values of OTE/SnO<inf>2</inf> /(ZnPc·4<sup>4-</sup>/Li<sup>+</sup>@C<inf>60</inf> )<inf>n</inf> were much higher than the sum of the two IPCE values of the individual systems OTE/SnO<inf>2</inf> /(Li<sup>+</sup>@C<inf>60</inf> )<inf>n</inf> and OTE/SnO<inf>2</inf> /(ZnPc·4<sup>4-</sup>)<inf>n</inf> , covering the near-infrared region.

Original languageEnglish
Pages (from-to)7690-7697
Number of pages8
JournalJournal of Physical Chemistry B
Volume119
Issue number24
DOIs
Publication statusPublished - 2015 Jun 18

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

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