Thioxanthone Dioxide Triplet States Have Low Oxygen Quenching Rate Constants

Jockusch S., Kazancioglu E. O., Karaca N., ARSU N., Landgraf S., Ogilby P. R.

Journal of Physical Chemistry B, cilt.128, sa.1, ss.244-249, 2024 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 128 Sayı: 1
  • Basım Tarihi: 2024
  • Doi Numarası: 10.1021/acs.jpcb.3c06077
  • Dergi Adı: Journal of Physical Chemistry B
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Applied Science & Technology Source, Aquatic Science & Fisheries Abstracts (ASFA), Chemical Abstracts Core, Chimica, Compendex, Computer & Applied Sciences, MEDLINE
  • Sayfa Sayıları: ss.244-249
  • Yıldız Teknik Üniversitesi Adresli: Evet

Özet

With few exceptions, triplet excited states of organic molecules, 3M1, are quenched by ground state molecular oxygen, O2(X3Σg-), with rate constants kq greater than ∼109 M-1 s-1 in fluid solutions. If the energy of the triplet state is above 94 kJ/mol, then such quenching can result in the sensitized production of singlet oxygen, O2(a1Δg). In the interaction between 3M1 and O2(X3Σg-), the magnitudes of both kq and the yield of the O2(a1Δg) depend appreciably on mixing with the M-O2 charge-transfer state. Here, we report that triplet states of several thioxanthen-9-one-10,10-dioxide derivatives have unusually low kq values (as low as ∼1 × 108 M-1 s-1) but have quantum yields for the photosensitized production of O2(a1Δg) that approach unity. Because these molecules possess high oxidation potentials (∼3.5 V vs SCE), we suggest that charge transfer character in the 3M1-O2(X3Σg-) encounter complex is reduced, thereby lowering kq while maintaining high O2(a1Δg) yields. These results provide important experimental support for existing models for the quenching of organic molecule excited states by O2(X3Σg-).