Interplay between the Glass Transition Temperature, Analyte Diffusion, and Fluorescence Quenching for Detection of...

Efficient detection of chemical analytes using fluorescence-based sensors necessitates an in-depth understanding of the physical interaction between the analyte molecules and the sensor films. This study explores the interplay between the thermal properties of a series of triphenylamine-centered fluorescent dendrimers with different glass transition temperatures (T_g) for detecting nitroaromatic explosives. When exposed to 4-nitrotoluene (pNT) vapors, biphasic diffusion kinetics were observed for all the dendrimers, corresponding to Super Case II kinetics, suggesting rapid film swelling during initial analyte uptake. The diffusion kinetics were further analyzed using a diffusion-relaxation model, where a strong T_g dependence was observed for both the initial concentration-driven diffusion phase and the slower film relaxation phase. Additionally, a difference in kinetics between analyte uptake and release was observed. The photoluminescence (PL) kinetics also showed a T_g dependence, with more efficient PL recovery observed for films composed of dendrimers that had a lower T_g. Rapid quenching of over 40% with little PL recovery was seen in the dendrimer with the highest T_g (107 °C), while a smaller quench with efficient PL recovery was observed in the dendrimer that had a T_g close to room temperature. The results highlight the critical role of the thermal properties of sensor films in achieving rapid and sensitive detection.