Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers.

Two iridium(III) binuclear photosensitizers, [Ir(dFCF3ppy)2(N-N)Ir(dFCF3ppy)2]2+, where N-N is tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine (Ir-TPPHZ) and 1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene (Ir-TAPHAT) are reported for iodide, bromide, and chloride photooxidation in acetonitrile and acetonitrile/water mixtures using blue-light irradiation. Excited-state reduction potentials Ered* of +2.02 and +2.09 V vs NHE were determined for Ir-TPPHZ and Ir-TAPHAT, respectively. Both photosensitizers' excited states were efficiently quenched by iodide, bromide, and chloride with quenching rate constants in the (3.5-9.2) × 1010 and (0.0036-2.9) × 1010 M-1 s-1 ranges in neat acetonitrile and acetonitrile/water mixtures, respectively. Nanosecond transient absorption spectroscopy provided unambiguous evidence of reductive excited-state electron transfer, with all halides in the solvent mixtures containing up to 50% water. Cage-escape yields were large (55-96%) in acetonitrile and dropped below 32% in 50:50 acetonitrile/water mixtures.

报道了两种铱（III）双核光敏剂，[Ir(dFCF3ppy)2(N - N)Ir(dFCF3ppy)2]2+，其中N - N为四吡啶并[3,2 - a:2',3' - c:3″,2″ - h:2‴,3‴ - j]吩嗪（Ir - TPPHZ）和1,4,5,8 - 四氮杂菲[9,10 - b] - 1,4,5,8,9,12 - 六氮杂三亚苯基（Ir - TAPHAT），用于在乙腈以及乙腈/水混合物中利用蓝光照射对碘离子、溴离子和氯离子进行光氧化。相对于标准氢电极（NHE），测定出Ir - TPPHZ和Ir - TAPHAT的激发态还原电位Ered*分别为 +2.02 V和 +2.09 V。在纯乙腈和乙腈/水混合物中，两种光敏剂的激发态均能被碘离子、溴离子和氯离子有效猝灭，猝灭速率常数分别在(3.5 - 9.2)×1010和(0.0036 - 2.9)×1010 M - 1 s - 1范围内。纳秒瞬态吸收光谱为还原激发态电子转移提供了确凿证据，在水含量高达50%的溶剂混合物中所有卤离子均如此。在乙腈中的笼逃逸产率较高（55 - 96%），而在50:50的乙腈/水混合物中则降至32%以下。