Photophysics of 1-methyllumichrome

Singlet and triplet excited states properties of 1-methyllumichrome have been studied in a series of non-polar, polar aprotic, and polar protic solvents, and adsorbed to a cellulose matrix. These observations are discussed in terms of the possible solvent-solute interactions. The absorption and emission spectra and the fluorescence lifetimes and quantum yields of 1-methyllumichrome have been measured, along with the transient absorption spectra. The excited state decays are all single-exponential, suggesting a single emitting species present in all cases. The spectroscopic data show that the singlet excited state properties of 1-methyllumichrome depend on the solute-solvent hydrogen interaction. Significant changes in fluorescence quantum yields and fluorescence lifetimes were recorded and explained by variations of the non-radiative decay rate constant. Placing the 1-methyllumichrome in a restricted environment caused pronounced changes in its behaviour under laser flash photolysis. Transient absorption measurements of 1-methyllumichrome in H2O+β-CD and in a cellulose matrix, provided the spectra of the radical anion and of the triplet excited state of the 1-methyllumichrome anion, respectively. Singlet oxygen is shown to be photosensitised in high yield, and this observation provides an insight into possible photodegradation pathways mediated by this molecule. In addition to the experiments, the nature of the electronic structure of 1-methyllumichrome has been studied by means of the time-dependent density functional theory.