Solution processed thin films of an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu₂[Pc(15C5)₄]₂[Pc(OC₁₀H₂₁)₈], have been prepared from three different methods: self-assembly (SA) annealed in solvent vapor, quasi-Langmuir–Shäfer (QLS) and drop casting methods. In particular, we successfully developed a simple QLS process for fabricating ordered multilayers with a good thickness control. The films prepared from three different methods were characterized by a wide range of methods including electronic absorption spectra, IR, X-ray diffraction, atomic force microscopy (AFM), and current–voltage (I–V) measurements. J-type aggregates have been formed with the increasing degree of order of molecular stacking Cast < QLS < SA films. Moreover, the gas sensing behavior of the three types of films was investigated towards ozone in the 8–300 ppb range. Unexpectedly good sensitive, stable and reproducible responses to O₃ gas are obtained for these kinds of ultra-thin solution processed films in a fast response/recovery cycle of only 1/4 min. The response of Eu₂[Pc(15C5)₄]₂[Pc(OC₁₀H₂₁)₈] films is linearly correlated to the ozone concentration. The interaction between the Eu₂[Pc(15C5)₄]₂[Pc(OC₁₀H₂₁)₈] films and different ozone concentrations was found to follow first-order kinetics. Strikingly, QLS films showed the most stable response and the largest average sensor response rate constant among the three types of films.

New organic devices including a heterojunction between a semiconducting molecular material (MS) – lutetium bisphthalocyanine (LuPc₂) – and a doped insulator (DI) – copper phthalocyanine (Cu(F_nPc), where n = 0, 8, 16) – are designed and studied as transducers for redox-active species sensing.

Organic heterostructures have emerged as highly promising transducers to realize high performance gas sensors. The key reason for such a huge interest in these devices is the associated organic heterojunction effect in which opposite free charges are accumulated at the interface making it highly conducting, which can be exploited in producing highly sensitive and faster response kinetics gas sensors. Metal phthalocyanines (MPc) have been extensively studied to fabricate organic heterostructures because of the large possibilities of structural engineering which are correlated with their bulk thin film properties. Accordingly, in this review, we have performed a comprehensive literature survey of the recent researches reported about MPc based organic heterostructures and their application in gas sensors. These heterostructures were used in Organic Field-Effect Transistor and Molecular Semiconductor—Doped Insulator sensing device configurations, in which change in their electrical properties such as field-effect mobility and saturation current in the former and current at a fixed bias in the latter under redox gases exposure were assessed to determine the chemosensing performances. These sensing devices have shown very high sensitivity to redox gases like nitrogen dioxide (NO₂), ozone and ammonia (NH₃), which monitoring is indispensable for implementing environmental guidelines. Some of these sensors exhibited ultrahigh sensitivity to NH₃ demonstrated by a detection limit of 140 ppb and excellent signal stability under variable humidity, making them among the best NH₃ sensors.

The semiconducting properties of the heteroleptic and homoleptic bis(phthalocyaninato) holmium complexes bearing electron-withdrawing phenoxy substituents at the phthalocyanine periphery, namely Ho(Pc)[Pc(OPh)₈] (1) and Ho[Pc(OPh)₈]₂ (2) [Pc = unsubstituted phthalocyaninate; Pc(OPh)₈ = 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninate] have been investigated comparatively. Using a solution-based Quasi–Langmuir–Shäfer (QLS) method, the thin solid films of the two compounds were fabricated. The structure and properties of the thin films were investigated by UV-vis absorption spectra, X-ray diffraction (XRD) and atomic force microscopy (AFM). Experimental results indicated that H-type molecular stacking mode with the common preferential molecular “edge-on” orientation relative to the substrate has been formed, and the intermolecular face-to-face π–π interaction and film microstructures are effectively improve by increasing the number of phenoxy substituents of the Pc periphery within the double-decker complexes. The electrical conductivity of Ho(Pc)[Pc(OPh)₈] films was measured to be approximately 4 orders of magnitude larger than that of Ho[Pc(OPh)₈]₂ films, indicating significant effect of peripheral electron-withdrawing phenoxy groups on conducting behaviour of bis(phthalocyaninato) holmium complexes. In addition, the gas sensing behaviour of the QLS films of 1 and 2 toward electron donating gas, NH₃ , was investigated in the concentration range of 15–800 ppm. Surprisingly, contrary responses towards NH₃ were found for the QLS films of 1 and 2. In the presence of NH₃ , the conductivity of the films of Ho(Pc)[Pc(OPh)₈] (1) decreased while the conductivity of the films of Ho[Pc(OPh)₈]₂ (2) increased. This observation clearly demonstrated the p- and n-type semiconducting nature for 1 and 2, respectively. Furthermore, compared to the heteroleptic 1 having a hole mobility of 1.7 × 10⁻⁴ cm² V⁻¹ s⁻¹, homoleptic 2 exhibits an electron mobility as high as 0.54 cm² V⁻¹ s⁻¹. Therefore, the inversion of the semiconducting nature of the double-deckers from p- to n-type can be successfully and easily realized just by increasing the number of peripheral phenoxy groups attached to the conjugated Pc cores.