Near-Infrared Photoelectrochemical Conversion via Photoinduced Charge Separation in Supramolecular Complexes of Anionic Phthalocyanines with Li+@C60

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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Two phthalocyanines possessing carboxylate groups ((TBA)4 H2 Pc·1 and (TBA)4 H2 Pc·2) form 1:2 supramolecular complexes with lithium cation-encapsulated C60 (Li+@C60 ) [H2 Pc·14-/(Li+@C60 )2 and H2 Pc·24-/(Li+@C60 )2 ] in a polar mixed solvent. From the UV-vis spectral changes, the binding constants (K) were estimated as ca. 1012 M-2. 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 H2 Pc·24-/(Li+@C60 )2 , which is the longest CS lifetime among the porphyrinoid/fullerene supramolecular complexes. H2 Pc·14-/(Li+@C60 )2 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-1 from the temperature dependence of the rate constant for the charge recombination of the CS state of H2 Pc·14-/(Li+@C60 )2 . 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+@C60 were also prepared and investigated. The ZnPc·44-/Li+@C60 supramolecular nanoclusters were assembled on the optically transparent electrode (OTE) of nanostructured SnO2 (OTE/SnO2 ) to construct the dye-sensitized solar cell. The IPCE (incident photon-to-photocurrent efficiency) values of OTE/SnO2 /(ZnPc·44-/Li+@C60 )n were much higher than the sum of the two IPCE values of the individual systems OTE/SnO2 /(Li+@C60 )n and OTE/SnO2 /(ZnPc·44-)n , covering the near-infrared region.

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

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© 2015 American Chemical Society.


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