PH-responsive switching of near-infrared absorption of a diradical complex of PtII and 3,4-diaminobenzoate formed in aqueous solutions

Kousaku Tamura, Atsuko Masuya, Nobuhiko Iki, Yasunori Ohba, Seigo Yamauchi, Hitoshi Hoshino

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


In alkaline aqueous solutions, 3,4-diaminobenzoate (H2( 2LPDA)-) reacts with PtII to form a 1:2 (Pt:L) complex that intensely absorbs near-infrared (NIR) light at 713 nm ( = 8.0 × 104 M-1 cm-1). The absorption disappeared at pH < 3 (in DMSO), showing pH-responsive switching of the NIR absorption. By comparing the NIR-absorbing behavior of this complex to that of a complex, [PtII(1LISQ)2] 2-, containing the analogous phenylenediamine ligand [( 1LISQ)2- = o-diiminobenzosemiquinonate radical], the complex can be formulated as [PtII(2L ISQ)2]2-. The assignment of the entity was consistent with the redox and spectroelectrochemical behaviors and electronic spin resonance (ESR) spectroscopy. First, one-electron oxidation of [Pt II(2LISQ)2]2- formed an ESR-silent complex assignable to the dimeric complex [{PtII( 2LISQ)(2LIBQ)}2] 2- [(2LIBQ) = o-iminobenzoquinone form] in which the two radical centers at (2LISQ)2- were antiferromagnetically coupled. Second, the one-electron reduced complex of [PtII(2LISQ)2]2- exhibited an ESR signal attributed to [PtII(2L ISQ)(2LPDA)]3-; 34% of the electronic spin was located at the PtII center rather than on the (2LISQ)2- moiety. The pH-responsive switching-off of the NIR absorption was thus rationally explained by oxidation of [Pt II(2LISQ)2]2- to [{PtII(2LISQ)(2LIBQ)} 2]2- by the increase of the rest potential of the solution in the lower pH region.

Original languageEnglish
Pages (from-to)81-86
Number of pages6
JournalInorganica Chimica Acta
Issue number1
Publication statusPublished - 2011 Nov 30


  • Near infrared light
  • Pt
  • Radical complex
  • Redox
  • o-Phenylenediamine

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


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