Laserspektroskopische Untersuchungen zur Dynamik von ionischen Flüssigkeiten mit Hilfe molekularer Sonden

Abstract

Ionic liquids have been studied by transient absorption spectroscopy. Relaxation processes after photo excitation of molecular probes were used as an indicator to study the microscopic environment in ionic liquids and their mixtures with organic solvents. The introduction of a carbonyl group in a carotenoid leads to a powerful probe for studying the polarity and solvation dynamics of ionic liquids. The molecular probes 12'-apo-beta-carotenoic-12'-acid and 12'-apo-β-carotenoic-12'-al were excited to the S(2) state. Internal conversion occurred within 100 fs to a single S(1)/ICT state with intramolecular charge transfer character. This state exhibits characteristic excited state absorption band-shifts due to time-dependent solvation, which appears to be a general feature of carbonyl apocarotenoids with polarity-dependent S(1)/ICT lifetimes. Another approach to characterize the microscopic properties of ionic liquids is mixing with organic solvents. For the measurements of these binary mixtures, the molecular probe 12'-apo-beta-carotenoic-12'-acid was used. It is shown that the polarity of the microscopic environment of this probe in [C6mim]+ [Tf2N]- does not change up to a high dilution with organic solvents. Ionic liquids can be used as electrolyte in dye-sensitized solar cells. A lot of progress has been made when it comes to efficiency but still there is a lack of knowledge about the interaction between the dyes and the electrolyte. In this work a class of indoline based dyes has been studied. It is shown that the dye D205 exhibits the highest measured lifetime of the excited state. This could lead to a higher light harvesting efficiency compared to the other investigated dyes.