AROMATIC KETONES AS STANDARDS FOR SINGLET MOLECULAR-OXYGEN O-2(1-DELTA(G)) PHOTOSENSITIZATION - TIME-RESOLVED PHOTOACOUSTIC AND NEAR-IR EMISSION STUDIES

Time-resolved near-IR emission and optoacoustic calorimetry studies we re carried out on the aromatic ketones phenalenone, benzanthrone, 4-ph enylbenzophenone and the benzophenone-naphthalene (0.1 M) system in or der to assess their adoption as solvent-independent standards for sing let molecular oxygen O-2((1) Delta(g)) photosensitization. All compoun ds show quantum yields of O-2((1) Delta(g)) production (phi(Delta)) in the range 0.9-1 in cyclohexane. Increasing solvent polarity or protic character reduces the phi(Delta) values for all sensitizers except ph enalenone. Laser-induced optoacoustic calorimetry was used to obtain t he absolute phi(Delta) values for the latter compound by applying both maximum amplitude and deconvolution methods. The former yields highly precise results (3%-5% uncertainty) and has been chosen for standardi zation purposes. The deconvolution method yields both kinetic and quan tum yield data, albeit with lower precision (10%-15% uncertainty).