In this study, colorimetric as well as chemical studies of commercially available fluorescent brightening agents (FBAs) are conducted. Thereby, special attention is given to polyethylene glycol (PEG) with varying molar masses, which is a known carrier for "boosting" and "activating" fluorescence and ethylene glycol (EG). While the colorimetrical analysis focuses on printed laboratory FBAinks containing liquid FBAs and in selected cases PEG, the chemical analysis is performed detached from the molecular environment "paper".
It is shown, that the chain-length of PEG has a significant impact on the obtainable quantum yield and therefore emission intensity. Based on spectral analysis, it is concluded that PEG decreases the reaction rate of the isomerization reaction (due to a hindering of the twist of the C=C double bond) resulting in longer periods in which the excited state of the trans-isomer can exist. This leads to an increased amount of fluorescence from the excited trans-isomers. Hence, the obtained quantum yield is increased. Quantum yield increases from 33% Qeff (in pure water) to 60% (in 30% PEG 1000) are reported.