Molekyylin sisäinen virittyneen tilan protoninsiirto 10-hydroksibentso[h]kinoliinijohdannaisissa

If a molecule contains a proton donor and a proton acceptor group in close proximity, an intramolecular hydrogen bond may be formed between the groups. Upon electronic excitation, a proton transfer from the donor to the acceptor is possible. This process is called an excited-state intramolecular proton transfer (ESIPT). The ESIPT processes can be studied with spectroscopic techniques, because the different tautomers of an ESIPT compound have different spectroscopic properties. The energy difference between the ground state and first excited state is smaller for the proton transfer tautomer than for the normal tautomer, and thus the fluorescence bands of these two species are located at quite different wavelengths. One of the most promising compounds for ESIPT applications is 10-hydroxybenzo[h]quinoline (HBQ). Due to its restricted geometry and the specific alignment of oxygen and nitrogen atoms, this compound possesses an exceptionally strong intramolecular hydrogen bond. Thus, the ESIPT reaction is fast and does not suffer from solvent perturbation, not even in protic solvents. In this Thesis, a systematic study on the substituent effect on the ESIPT kinetics of HBQ derivatives is presented. The used measurement techniques include steady-state absorption and emission spectroscopy as well as time-resolved methods for determining fluorescence lifetimes. Several different HBQ derivatives are studied, and the performance of compounds with different substituents at the same position is compared. Furthermore, the effect of solvent polarity on the ESIPT rate is investigated by repeating the measurements in solvents with different polarities. ESIPT is reported to occur in most of the studied compounds. An electron-donating substituent at the methylenepyridine part of the molecule shifts the fluorescence emission of the proton transfer tautomer to shorter wavelengths compared to the non-substituted HBQ. An electron-withdrawing substituent has the opposite effect, respectively. Furthermore, the electron-withdrawing substituents induce an increase in the relaxation rate of the proton transfer tautomer, caused by the lowered basicity and proton-binding ability of the proton acceptor moiety. A remarkable solvent effect in the proton transfer relaxation rate is observed only for two compounds with a nitro substituent. Perhaps the position and the electron-withdrawing character of the substituent weaken the intramolecular hydrogen bond in these compounds, making it more vulnerable to perturbation by polar solvents. /Kir1