Narrow Results

Two asymmetrical amphiphilic phthalocyanines simultaneously containing hydrophobic alkoxy and hydrophilic 15-crown-5-ether substituents at the phthalocyanine periphery H₂{Pc(15C5)₃[(OC₈H₁₇)₂]} (Pc-1) and H₂{Pc(15C5)[(OC₈H₁₇)₆]} (Pc-2) and their symmetrical analogue H₂[Pc(OC₈H₁₇)₈] (Pc-3) have been synthesized and characterized. The _Pc-n/CdS (n = 1, 2 and 3, respectively) hybrid films are obtained successfully via a simple quasi-Langmuir–Shäfer (QLS) method using H₂S-vapor annealing over the Pc-n/Cd²⁺ self-assembled film formed at the interface of the air/CdCl₂ aqueous solution. The film-structure and properties of both the hybrid Pc-n/CdS and pure Pc-n films are comparatively studied by a wide range of methods including UV-vis, polarized UV-vis, XRD, SEM and I–V measurements. Experimental results exhibit a slipped co-facial stacking mode in an “edge-on” conformation (H-type aggregate) formed for the phthalocyanine molecules in both pure Pc-n films and the corresponding Pc-n/CdS hybrid films, with increasing intermolecular π–π interactions in the order of Pc-n < Pc-n/CdS and Pc-3/CdS < Pc-2/CdS < Pc-1/CdS, respectively. Accordingly, filmmicrostructures, crystallinity and conductivity are effectively improved by introducing CdS nanoparticles into the 15-crown-5-substituented phthalocyanines forming Pc-1/CdS and Pc-2/CdS hybrid films. These render excellent sensing performance towards NO₂ in the 0.05–2.5 ppm range within a fast dynamic exposure period of 30 s. Strikingly, Pc-1/CdS hybrid film presents an unprecedented high sensitivity of 157.3%.ppm^-1vs. very low NO2 concentration range of 0.05~0.25 ppm, achieving one of the best room temperature sensing performances in terms of high sensitivity, rapid responsibility and low detection limit among self-assembled film-based NO₂ sensors.