Excited state processes of 2-butylamino-6-methyl-4-nitropyridine N-oxide in nonpolar solvents. A transient absorption spectroscopy study.

Earlier steady-state fluorescence studies showed that 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) can undergo fast excited-state intramolecular proton transfer (ESIPT). In a nonpolar solvent such as n-octane, both normal and tautomeric fluorescence was observed. Strikingly, the relative ratio of those two emission bands and the fluorescence quantum yield of the normal emission were found to depend on the excitation wavelength in violation of the Kasha-Vavilov rule.

High-resolution steady-state and time-resolved luminescence studies on the complexes of Eu(III) with aromatic or aliphatic carboxylic acids.

Eu(III) luminescence spectroscopy, both in the steady-state and the time-resolved mode, is an appropriate technique to study the properties of complexes between heavy metal ions and humic substances (HS), which play a key role in the distribution of metal species in the environment. Unfortunately, room temperature luminescence spectra of Eu(III) complexes with aromatic and aliphatic carboxylic acids - model compounds of HS binding sites - are too broad to fully exploit their potential analytical information content. It is shown that under cryogenic conditions fluorescence-line-narrowing (FLN) is achieved, and the highly resolved spectra provide detailed information on the complexes.

Excited-state double proton transfer in 1H-pyrazolo[3,4-b]quinoline dimers.

Pyrazoloquinolines are highly fluorescent, both in liquid solutions and in the solid state, which makes them good candidates for various optical devices. The aim of the current work is to understand the photochemical behavior of pyrazolo[3,4-b]quinoline (PQ), which is quite complicated since in n-alkane solvents PQ tends to form strong complexes with protic solvent constituents (often present as minor impurities), as well as dimers. Both types of H-bond complexes were studied systematically by temperature-dependent conventional absorption and fluorescence spectroscopy; the effect of protic solvent constituents was mimicked by varying the ethanol concentration in n-octane in the range from 0.

Cryogenic fluorescence and absorption spectroscopy studies on monomeric and dimeric species of 2-butylamino-6-methyl-4-nitropyridine N-oxide.

2-Butylamino-6-methyl-4-nitropyridine-N-oxide (2B6M) belongs to a group of compounds that can undergo not only excited-state intra-, but also intermolecular proton transfer. The latter of course requires the presence of dimeric species. Previously, we have shown that for 2B6M in aprotic non-polar solvents in the liquid state such dimers play no role.

Intramolecular proton-transfer processes starting at higher excited states: a fluorescence study on 2-butylamino-6-methyl-4-nitropyridine N-oxide in nonpolar solutions.

This article describes the exceptional photophysics of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M). It is known from the literature that this compound may undergo excited-state intra- or intermolecular proton-transfer reactions. In nonpolar solvents, 2B6M exhibits an unusual fluorescence behavior: there is a substantial difference between the relative band intensities of the excitation and absorption spectra.