Fine-Tuning Intermolecular and Intramolecular Interactions to Build the Films of Tris(Phthalocyaninato) Rare Earth Complexes and Their Comparative Performances in Ambipolar Gas Sensing

High-performance ambipolar chemical sensors toward electron-detonating NH3 and electron-accepting NO2 are obtained based on the solution-based films of two ambipolar (p-fluoro) phenoxy substituted tris(phthalocyaninato) rare earth semiconductors with different metal ions, named Gd-2[Pc(OPhF)(8)](3) (1) and Tb-2[Pc(OPhF)(8)](3)(2). Measurements over the films fabricated from 1 and 2 by a simple quasi-Langmuir-Shafer (QLS) method reveal their ambipolar semiconductor nature, with a p-type response in NH3 sensing and n-type response in NO2 sensing, associated with not only suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels but also the different electronic induction effects of the analytes. Interestingly, the devices from the QLS film of 2 with a weaker intermolecular pi-pi stacking in J-type (edge-to-edge) packing mode display much better sensing properties to both NH3 and NO2, compared to those from QLS film of 1 with a stronger intermolecular pi-pi stacking in the H-type (face-to-face) packing mode. This is mainly because of the larger specific surface area from the J-aggregate with the more uniform-sized nanoparticles for the QLS film of 2. In particular, the highly sensitive, stable, and reproducible responses to 1-20-ppm NH3 with a limit of detection of 0.15 ppm only in 1 min are obtained from the QLS film of 2 for the first time. This paper unravels, first, the effect of central metal ions of sandwich triple-deckers on molecular stacking mode, film structure, and gas sensing performances, which would be helpful for designing and preparing high-performance ambipolar gas sensor devices by combining the molecular design and the device fabrication technique.