Photoacoustic calorimetry was used to measure the quantum yields of singlet molecular oxygen production by the triplet states of tetraphenylporphyrin (TPP), ZnÀTPP and CuÀTPP in toluene, yielding values of 0.67 AE 0.14, 0.68 AE 0.19 and 0.03 AE 0.01, respectively. We show that a novel dichlorophenyl derivative of Zn À TPP is capable of singlet-oxygen production with a 0.90 AE 0.07 quantum yield. The synthesis and characterisation of a new photostable chlorin with high absorptivity in the red that is capable of singlet-oxygen production with 0.54 AE 0.06 quantum yield is described. Our results suggest that chlorinated chlorins may be interesting new sensitisers for photodynamic therapy.

The photophysics of halogenated and metallated tetrakisphenylporphyrins is investigated using single-photon counting, photoacoustic calorimetry and luminescence techniques. The radiationless transition rates in these and related molecules are interpreted with a quantum-mechanical tunnelling model modified to include the effect of spin-orbit coupling in the intersystem crossing rates. It is shown that tetrakisphenylporphyrins with halogens in the ortho positions have long-lived triplet states that are formed in high yields. Ó

A general analysis of the steps of the Rothemund reaction, allowed for a better understanding and a significant improvement of this reaction as a synthetic method in some of the previously known difficult syntheses.

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Three significant modifications to existing methods for the preparation of the important 5,10,15,20-tetrakisarylporphyrins have improved isolated yields, simplified work-up and made large-scale synthesis feasible. Two teuakisalkylporphyrins were also produced. A two-stage approach using hydrogen peroxide in acetic acid as second stage oxidant gave good yields but for ease of isolation and convenience in worldng on a large scale, the one-pot approach is preferred. No one method appears to be suitable for all such tetrak~arylporphyrins and, for best yields, the method of preparation needs to be chosen carefully. Application of statistical opthisation techniques (factorial two design and simplex operation) led to considerably enhanced yields for the one-pot method. For one of the two-stage modifications, significant amounts of chlorins were observed, sometimes of such magnitude as to make it suitable as a method for their preparation.