Characterization of carbazole derivatives and modulation of their luminescence

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Characterization of carbazole derivatives and modulation of their luminescence

This thesis investigates the effects of intermolecular interactions such as hydrogen bonding, halogen bonding and ionic interactions on the emission of organic compounds in solution and solid state. The study focuses on carbazole derivatives with either hydrogen or halogen bond acceptor and donor moieties. These non-covalent bond donors and acceptors are characterized using absorption and emission spectroscopy as well as time-correlated single photon counting. In the solid state, the films are also characterized using optical profilometry and digital holographic microscopy. Titration series using pentafluoroiodobenzene, phenol, benzenesulfonic acid and pyridine are prepared to study the emission modulation induced by the non-covalent bonding. In addition to emission spectra, the changes in the excited-state lifetime and emission quantum yields are determined. The effects of non-covalent bonding in the solid state are studied forming polymer-chromophore complexes capable of weak interactions. Polystyrene is used as a reference polymer, poly(vinyl phenol) as a hydrogen bond donor, poly(4-vinyl pyridine) as a halogen bond acceptor, and finally poly(styrenesulfonic acid) in the formation of ionic interactions. Halogen bonding in solution induces intramolecular charge transfer that modulates the emission of the compound. The emission modulation results in increased emission intensity and a blue-shift in the emission spectra. Even greater effects can be seen with ionic interactions using benzenesulfonic acid which enhances the emission intensity and emission quantum yield up to 0.93. Weak hydrogen bonding did not result in emission modulation. Halogen bonding in solution was also studied using carbazole derivatives as halogen bond donors, but carbazole derivatives displayed greater potential as halogen bond acceptors than donors. Similar effects were also observed in the solid state, only in less significant amounts.

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