Characterization of carbazole derivatives and modulation of their luminescence
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Karbatsolijohdannaisten luminesenssin modulaatio ja karakterisointi
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.