QUENCHING OF THE LUMINESCENCE OF SINGLET MOLECULAR-OXYGEN BY PHTHALOCYANINES AND NAPHTHALOCYANINES

Using the direct measurement of the photosensitized luminescence of singlet molecular oxygen (1O2) the rate constants (k(q)) have been determined for 1O2 quenching by the following phthalocyanines and naphthalocyanines in chloroform: tetra-(4-tret-butyl) phthalocyanine (I), octa-(3,6-butoxy)-phthalocyanine (II), tetra-(6-tret-butyl)-2,3-naphthalocyanine (III), aluminium tetra-(1-tert-phenyl)-2,3-naphthalocyanine (IV), tri-(n-hexylsiloxy)-derivatives of silicon-(V), tin-(VI), aluminium-(VII) and gallium-(VIII) 2,3-naphthalocyanine. The following k(q) values were obtained (kq.10(-8), M-1(s)-1): 2.9 (I), 59 (II), 100 (III), 20 (IV), 3.9 (V), 53 (VI), 33 (VII), 110 (VIII). The data suggest that quenching by (I) is mostly caused by the formation of charge transfer complexes in collisions between 1O2 and the quencher. The energy transfer from 1O2 to the low-lying triplet states of the quenchers strongly contributes into 1O2 quenching by (II)-(VIII). It was concluded that phthalocyanines and naphthalocyanines might be efficient inhibitors of photodestructive processes in photochemical and photobiological systems.