inorganic chemistry

(H 2 BPurhep), as in chlorins (81,93,94). The success of these
strategies can be best evaluated in terms of the photodecomposi-
tion quantum yields of the sensitizers.
The photodecomposition quantum yield is defined as

Fpd¼

initial rate of disappearance of photosensitizer molecules

initial rate of absorption of photons

(19)

Table IV presentsFpdvalues taken from the literature or calcu-
lated from data in the literature for various photosensitizers
with the structures presented in Fig. 8. Assuming that the oxida-
tion potentials along the series of tetrahydroxyphenyl porphyrin
(H 2 TOHPP), chlorin (H 2 TOHPC, commercialized as Foscan),

TABLE IV

PHOTODEGRADATION ANDSINGLETOXYGENQUANTUMYIELDS OFPHOTOSENSITIZERS,AND
TRIPLETQUENCHINGRATECONSTANTS INAERATEDSOLUTIONS

Fpd 106 FD kq/kdiffa

PBS PBS:methanol Methanol

Photofrinb 55 0.36 0.12
H 2 TOHPPc 3.8 0.46 0.17
H 2 TOHPC (Foscan)c 33 0.43 0.16
H 2 TOHPBc 1500 0.43 0.23
PdBPheo (Tookad)d 1800  1
Stakel (PdBPheo
derivative)e

2800  0

H 2 TClPBOHf,g 284 296 35 0.43 0.43
H 2 TFPBMetf 81 0.63
H 2 TCl 2 PBEtf,h 6 0.66 0.33
H 2 BPurHepi 0.46 0.33

aIn methanol, ethanol, benzonitrile, and, in the case of H 2 TClPBOH, aqueous solutions,

kq/kdiff¼0.11 is expected in the absence of charge transfer and should increase to 0.44

with charge transfer.

bFrom Refs. ( 95 ) and ( 96 ); the value ofFDwas measured for a 10mM PBS solution of

hematoporphyrin derivative( 97 ).

cFrom Refs. (98,99) and 99 , withFDin methanol.

dIn acetone using data fromRef. ( 79 ).

eUsing data fromRef. ( 80 ), but the broadening of the absorption bands shows that the

photosensitizer is aggregated and this typically diminishes the photodegradation.

fFrom Ref. ( 90 ).

gFrom Ref. ( 100 ).

hFrom Ref. ( 65 ).

iFrom Ref. ( 101 ), but the rate constants refer to H 2 BPur in benzonitrile according to

Ref. ( 82 ).

220 LUIS G. ARNAUT