Generation and deactivation of ¹O₂ (¹Δ) by helianthrene and helianthrene‐derivatives

Abstract

Chemical Kinetics / Energy Transfer / Photochemistry / Singlet Oxygen The photooxygenation of helianthrene (H), mesodiphenylhelianthrene (MDH) and mesodiphenylbenzhelianthrene (MDBH) has been studied kinetically by several independent methods in different solvents. The results indicate that singlet oxygen ('A) is generated only by oxygen quenching of the lowest triplet states via the process: TI + 'Z -+ S + 'A, which occurs with unit efficiency for all three hydrocarbons. H is the most reactive 'A-acceptor hitherto known. In solvents of low viscosity like acetone the rate constant of reaction is k7 = 4.6.109 M-' s-' . MDH and MDBH are not only very reactive 'A-acceptors but also efficient 'A-quenchers. In a mixture of toluene and methanol (1 Vol.%) for MDBH the rate constants of physical quenching and photooxygenation amount to kll = 6.3. lo9 M-' s-' and k7 = 0.2.109 M-' s-'.

Potential Photosensitizers for Photodynamic Tumor Therapy—i. Photophysical Properties of Two Chlorin Derivatives

“…Quantum yields of 'A, formation (@iH1-) and rate constants of physical 'A, quenching (kSHLJ. @xH1and kSHL were determined photochemically using MDH as IA, acceptor (Acs et al, 1987). In air-saturated chloroform and carbon tetrachloride, measurements were carried out at three different chlorin concentrations in the range (2.5-10) X M .…”