The popularity of photodynamic therapy results from a cytotoxic effect achieved on target tissue without destroying healthy tissue. It is based on administration of a photosensitizer, light of the appropriate wavelength and reaction with molecular oxygen. The key process is transition of the photosensitizer to the triplet excited state and generation of reactive singlet oxygen. Therefore, the goal is to enhance the efficacy of the therapy by modifying properties of the photosensitizer. For this there is a need for a molecule of high quantum yields of a triplet excited state and a singlet oxygen. Target of the current research are porphyrins, of which the most interesting are meso-substitued porphyirins. Their substituents significantly change the value of mentioned quantum yields. Since number and type of substituents is adjustable, this is the focus of many studies and investigations. Here are shown the results of introduction of electrondonor and electron-acceptor groups to the porphyrin ring, as well as alkyl chains, silylation and halogenation. Also, here is given the overview of two techniques, pulse train fluorescence technique and measurement of the porphyrins in triplet excited state. Since the bromine derivative showed the highest quantum yield of triplet excited state (ΦT = 0.98) and silylated derivative the highest quantum yield of singlet oxygen (Φ∆ = 0.77), the promising porphyrins are the ones with bromine and silicon in the meso position. Also, the example of alkyl chains in meso position, gives the insight in the indirect impact of substituents on quantum yields. Alkyl chain with 22 carbon atoms is hydrophobic and it increases the aggregation of porphyrins in aquatic medium. In that way, the efficacy of photosensitizer is decreased (ΦT < 0.08). As opposed to these conclusions, results that cannot be interpreted with same certainty and need more research are metoxyphenyl group and fluorine in meso position.