Triangulenium cations: New sensitizers for singlet oxygen generation

NARAYANA PILLAI MANOJ; SUMALEKSHMY, S; NEVES PITTA, R; PETROSELLI GABRIELA; OLIVEROS ESTHER; BRAUN ANDRÉ M.

Riezlern

Simposio; Minisymposium Photochemie Optische Spektroskopie Sensorik; 2006

Singlet  oxygen  is  a  multifaceted  molecule  with  applications  ranging  from  synthesis  to materials  technology  and medicine.  The  role  of  singlet  oxygen  in  the  oxidative  stress  of biological  tissues as well as  its beneficial applications  in photodynamic  therapy demand a proper understanding of its generation and dynamics in biological media. Photosensitization offers a convenient way  to generate singlet oxygen  in vivo or  in vitro. The search  for new sensitizers  for  this purpose  is  in  the  focus of  research groups working in this area.   However the participation of singlet oxygen in this process has not been ruled out conclusively. Trioxatriangulenium (TOTA) cation exhibits a triplet energy of 228 kJM-1 and a quantum  yield  of  intersystem  crossing  of  0.57  in  water.  The  triplet  state  may  therefore transfer  efficiently  its  energy  to  molecular  oxygen  to  produce  singlet  oxygen.[3] Azatriangulenium cations (TATA) have similar photophysical properties and exhibit a robust photochemical  and  thermal  stability  compared  to  trioxatriangulenium  (TOTA)  cation. Azatriangulenium cations having long alkyl substituents on the N atoms can be solubilized in microheterogeneous  media  such  as  micelles  and  liposomes.  Steady–state  and  time–resolved measurements  of  singlet  oxygen  luminescence  at  1270  nm  showed  that  these cations  are  efficient  sensitizers  for  singlet  oxygen  generation,  and  corresponding experimental details and results are presented and discussed.