TY - JOUR
T1 - PH-responsive switching of near-infrared absorption of a diradical complex of PtII and 3,4-diaminobenzoate formed in aqueous solutions
AU - Tamura, Kousaku
AU - Masuya, Atsuko
AU - Iki, Nobuhiko
AU - Oba, Yasunori
AU - Yamauchi, Seigo
AU - Hoshino, Hitoshi
PY - 2011/11/30
Y1 - 2011/11/30
N2 - 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.
AB - 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.
KW - Near infrared light
KW - Pt
KW - Radical complex
KW - Redox
KW - o-Phenylenediamine
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U2 - 10.1016/j.ica.2011.08.018
DO - 10.1016/j.ica.2011.08.018
M3 - Article
AN - SCOPUS:80054991806
SN - 0020-1693
VL - 378
SP - 81
EP - 86
JO - Inorganica Chimica Acta
JF - Inorganica Chimica Acta
IS - 1
ER -