Different porphyrin conformations are believed to play a role in controlling the cofactor properties in natural tetrapyrrole-protein complexes. In order to study the correlation between macrocycle nonplanarity and physicochemical properties in detail, a series of six porphyrins with graded degree of macrocycle distortion was investigated. These conformationally designed porphyrins are based on the successive introduction of β-ethyl groups into the tetraphenylporphyrin parent macrocycle and the degree of nonplanarity is dependent on the number and localization of the β-ethyl meso-phenyl interactions. The electronic properties of the complete series of porphyrins were investigated in solution. It was found that the singlet and triplet properties depend not only on the out-of-plane distortion parameter but also on the type of central metal. Moreover, it was found that macrocycle distortion affects the singlet state properties significantly stronger than the triplet properties. In addition, the efficiency of energy transfer to molecular oxygen was investigated. It was shown that the singlet oxygen quantum yield depends strongly on the triplet state lifetime of the porphyrins, resulting in differences between the decrease of intersystem crossing and singlet oxygen quantum yield. The observed gradual change of electronic parameters of base free tetraphenylporphyrins with increasing deformation of the macrocycle indicates the validity of using conformationally designed porphyrins to fine-tune photophysical properties.

In vivo measurement of singlet oxygen luminescence kinetics is affected by the heterogeneity of biological samples. Even though singlet oxygen luminescence detection is technically getting easier, the analysis of signals from biological samples is still far from quantitative real time surveillance as it is aspired by the community. In this paper small unilamellar vesicles (SUVs) are used for modelling the general behaviour of heterogeneous samples. The geometry of the SUVs can be determined independently using dynamic light scattering. Therefore an accurate theoretical description of the generation, deactivation and diffusion of the singlet oxygen is possible. The theoretical model developed here perfectly fits the experimental results. Thus the location of the singlet oxygen generating a photosensitizer molecule can be exactly determined from the kinetics of the singlet oxygen luminescence. The application of the used theoretical approach thus allows for accurate quantitative measurements in SUVs.

The Jablonski diagram describes the kinetics of electronic transitions of organic dyes by a rate constant model. A generalization of the Jablonski diagram is presented which allows one to account for polarization and anisotropy effects. To do this, the discontinuous distribution approach (DDA), which models rotational diffusion by discontinuous jumps of the molecule between the principal molecular orientations, is employed. Thus, both rotational diffusion and population dynamics can be modeled by a system of rate differential equations rather than by solving the equation of rotational diffusion, which considerable simplifies the numerics. The generalized Jablonski diagram fully describes the kinetics of any desired electronic and orientational relaxation processes. In particular, orientational relaxation can be calculated for an arbitrary initial distribution of excited molecules. Thus, the new model is especially suited for applications in non-linear spectroscopy since it is not restricted to the small signal limit as many other approaches are.