Investigation of structure, optical properties and chemical stability of the KL1421 pyridinium luminophore with high quantum yield

• New organic luminophores. • High quantum yield. • Good chemical stability. • Application in emergent conditions. This study reports on the synthesis sturcutre and optical properties of a novel pyridinium luminophore (KL1421). The main properties of the KL1421 have been modeled by quantum chemistry calculations using the B3LYP method. The structure, electronic, and optical properties of the KL1421 have been investigated by 1 H NMR, FT-IR, XRD, diffuse reflectance, and photoluminescence spectroscopy. The stability of the optical signal and application of the KL1421 as a gas sensor for the detection of water, ammonia, and acetic acid vapors were evaluated. Analysis of theoretical and experimental results exhibits a significant difference in the KL1421 optical properties due to limitations of the selected calculation model. Theoretical calculations have predicted a weak interaction between KL1421 and adsorbed water and ammonia molecules. No chemical interactions and phase transitions have been foreseen by calculations in the interaction between KL1421 and acetic acid. Experimental results showed non-covalent interaction and phase transitions after exposure to water and ammonia environment, and acetic acid, respectively. Weak interaction and crystallinity changes were observed by 1 H NMR, XRD, FTIR, and UV-Vis absorption spectra. Red shift of the absorption edge was found after interaction with target molecules, explained by the change of the HOMO-LUMO transition energy. Analysis of interaction by photoluminescence spectroscopy showed high quantum yield (QY) for the KL1421 (80 %) and high stability of the signal with low noise to signal ratio (3 %). Adsorption of the target molecules was irreversible, remaining physisorbed molecules onto KL1421 surface. It led to insignificant changes of QY (77-78 %) and slight red shift of photoluminescence peak position after exposure to water and ammonia. Strong interaction with acetic acid led to a decrease of the QY to 35 %, red shift of the emission peak position, and decrease of the photoluminescence intensity (60 %). Analysis of the structure and optical properties enables to propose mechanism of interaction between KL1421 and acetic acid, based on hydrogen bonding to the mesylate ion. The formation of new complexes induced phase transitions and changes in charge transfer mechanisms. We propose dual-mode measurements, based on photoluminescence and diffuse reflectance, to evaluate the strength of the interaction between KL1421 and volatile molecules. At this stage, the developed KL1421 luminophores didn’t show good sensitivity towards the selected target molecules. They show good potential as photoluminescent markers for emerging applications in environments with high humidity and pH. Improvement of sensor properties requires modification of the chemical structure and investigation of sensitivity towards other volatile acids.