Fluorescence spectroscopy is an indispensable analytical method in modern research. The complexity of luminescent systems usually requires the combination of several techniques.

In this work, novel donor-acceptor fluorescence dyes with potential applications in electro-optical devices, materials with non-linear optical properties and fluorescence sensors were characterized spectroscopically. For the targeted synthesis of these fluorophores

with specific fluorescence properties, a detailed understanding of their optical characteristics is essential.

An important part of this work was the optimization of dynamic and static fluorescence techniques for the spectroscopic characterization of donor-acceptor dyes. In particular, an excitation-emission-spectrometer has been supplemented by an integration sphere for the detection of solid state fluorescence. Furthermore, a newly designed TCSPC-experiment enables the analysis of excited states in solution as well as in the solid state.

A low-temperature sample holder was integrated in both experiments for static and dynamic fluorescence spectroscopy at temperatures down to 77 K.

In the second part of this work, a number of boron-based donor-acceptor-dyes, containing a 1,3,2-benzodiazaborolyl or a dicarba-closo-dodecarborane unit, were investigated

spectroscopically. For a comprehensive understanding of the relationship between the structure of dyes and their fluorescence properties, the spectroscopic studies were

supplemented by the results of TD-DFT calculations and X-ray structure analysis. Benzodiazaborolyl-based donor-acceptor dyes exhibit intense luminescence accompanied

by large Stokes shifts. The distinct solvatochromism of the emission confirms a strong change in the dipole moment between the ground state and the excited state which is

characteristic for donor-acceptor dyes. By the variation of the substituents at the nitrogen atoms of the benzodiazaborole, the originally electron donating character can be changed to an electron accepting behaviour. As a result, the benzodiazaborolyl moiety

offers the unique opportunity to create donor-acceptor dyes in which both functionalities originate from the same group of substances.

Systematic measurements revealed that ortho-carboranebased donor-acceptor dyes possess unexpected and complex emission properties which include dual fluorescence. UVemissions are due to local transitions while the low-energy emissions could be traced back to a charge-transfer-transition to an excited state with a geometry significantly different to the ground state. Benzodiazaborolyl-substituted ortho-carboranes exhibit

yellow to red emission in the solid state. Because of the high quantum yields of up to 70 %, these compounds are a promising candidate for technical applications.