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

Effect of co-adsorbate and hole transporting layer on the photoinduced charge separation at the TiO2-phthalocyanine interface

Understanding the primary processes of charge separation (CS) in solid-state dye-sensitized solar cells (DSSCs) and, in particular, analysis of the efficiency losses during these primary photoreactions is essential for designing new and efficient photosensitizers. Phthalocyanines (Pcs) are potentially interesting sensitizers having absorption in the red side of the optical spectrum and known to be efficient electron donors. However, the efficiencies of Pc-sensitized DSSCs are lower than that of the best DSSCs, which is commonly attributed to the aggregation tendency of Pcs. In this study, we employ ultrafast spectroscopy to discover why and how much does the aggregation affect the efficiency. The samples were prepared on a standard fluorine-doped tin oxide (FTO) substrates covered by a porous layer of TiO2nanoparticles, functionalized by a Pc sensitizer and filled by a hole transporting material (Spiro-MeOTAD). The study demonstrates that the aggregation can be suppressed gradually by using co-adsorbates, such as chenodeoxycholic acid (CDCA) and oleic acid, but rather high concentrations of co-adsorbate is required. Gradually, a few times improvement of quantum efficiency was observed at sensitizer/co-adsorbate ratio Pc/CDCA = 1:10 and higher. The time-resolved spectroscopy studies were complemented by standard photocurrent measurements of the same sample structures, which also confirmed gradual increase in photon-to-current conversion efficiency on mixing Pc with CDCAK.V. acknowledges the Doctoral Programme of Tampere University of Technology for the financial support. N.V.T. acknowledges NATO SPS project no. 985043. Financial support from Comunidad de Madrid, Spain (S2013/MIT2841, FOTOCARBON) and MINECO, Spain (CTQ2014- 52869-P and CTQ2017-85393-P) is acknowledged. IMDEA Nanociencia acknowledges support from the “Severo Ochoa” Programme for Centres of Excellence in R&D (MINECO, grant SEV-2016-0686)

Fluorescence enhancement of quinolines by protonation

A study of the fluorescence enhancement of isoquinoline, acridine (benzo[b]quinoline) and benzo[h]quinoline is reported with six organic acids of different pKa values. Protonation was found to be an effective tool in the fluorescence enhancement of quinolines. A significant increase in the fluorescence intensity is observed only when strong acids are used, resulting in an over 50-fold increase in fluorescence with trifluoroacetic or benzenesulfonic acid and isoquinoline in a 1.5 : 1 ratio. The benzenesulfonic acid was found to be the most effective in the protonation of the bases despite its higher pKa value compared to trifluoro- and trichloroacetic acid. The X-ray crystal structures of 14 salts reveal the charge-assisted hydrogen bond O⋯N distances to vary very little, from 2.560(2)–2.714(3) Å, with the exception of the isoquinolinium benzenesulfonate where the O⋯N distance of 2.862(7) Å is caused by additional intermolecular interactions in the solid-state.peerReviewe