Molecular Engineering of Porphyrin‐Tapes/Phthalocyanine Heterojunctions for a Highly Sensitive Ammonia Sensor

Abstract

The coexistence of a conjugated organic macrocyclic structure and a transition metal center provides MPor with numerous properties that fostered their use in catalysis, [2,3] theranostic, [4] and nonlinear optic. [5] Another application area of MPor is chemosensing, [6] in which interactions with a chemical analyte modifies the physical properties of MPor film that can be transduced into a measurable signal. Based on the nature of signal transductions, MPorbased optical, acoustic, magnetic, and electrical chemosensors have been developed [7] to detect myriad of species such as redox gases, [8] volatile organic compounds, [9] and inorganic biochemical species. [10] Particularly, MPor chemosensors based on electrical transductions such as chemiresistors, ChemFet, and conductometric sensors have drawn interests exploiting the semiconducting nature of MPor, which can be effectively tuned by adding substituents to its macrocyclic periphery or ligands at the metal center. Song et al. reported a chemiresistor based on highly ordered nanotubes of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin zinc(II) to selectively detect NO 2 at sub-ppm concentration. [11] Elsewhere, self-assembled monolayers of MPor films in ChemFet configuration were used to detect organic vapors and redox gases, exhibiting the strong influence of metal atom on sensors responses. [12,13] However, most of the MPor are poor conducting materials owing to low π-conjugation, limiting the sensors performances. To overcome this limitation, different approaches have been adopted such as forming a composite with more conducting materials like carbon nanotubes, [14,15] conductive polymers, [16,17] or metal oxides. [18,19] An alternative solution to the MPor low conductivity can be the formation of highly conjugated porphyrin polymers to extend the molecular π-system. However, the synthesis of conjugated porphyrin polymers requires significant synthetic efforts. In 2001, Tsuda and Osuka provided a new route toward the easy synthesis of directly fused metalloporphyrins, known as porphyrin tapes (Scheme 1). [20] Porphyrin tapes possess a series of outstanding properties such as electronic transitions in the IR region, [20] increased catalytic activity, [21] two-photon absorption, [22] and low conductance attenuation factors. [23,24] The synthesis of porphyrin tapes relies on the Modulating the interfacial charge alignments by molecular engineering in an organic heterojunction device is a smart strategy to improve its conductivity, which can be exploited in high-performance gas-sensor development. Herein, the fabrication of new organic heterojunction devices based on porphyrin tapes and phthalocyanines and their potentiality in ammonia sensing at different relative humidity (rh) are investigated. The devices are built using dry approach relying on oxidative chemical vapor deposition for simultaneous synthesis, doping, and deposition of the porphyrin tape layer and physical vapor deposition of phthalocyanine layer. The association of the porphyrin tapes with copper ph...

Conformational Control of Chemical Reactivity for Surface‐Confined Ru‐Porphyrins

“…Our findings with this model Ru-porphyrin/Ag(111) system are expected to be relevant for the elucidation to processes related to gas sensing, [33] and to supported single-atom catalysts (e.g. Ru-N4).…”

Photon assisted-inversion of majority charge carriers in molecular semiconductor-based organic heterojunctions

“…In particular, organic macrocycles like metal phthalocyanines (MPcs) are versatile molecular semiconductors in which the dynamics of the charge carriers (e and h + ) upon chemical doping by redox gases, such as nitrogen dioxide, ammonia and ozone, can be exploited for chemosensing studies. [10][11][12] MPc materials manifested a strong correlation between molecular level electronic properties with thin film electrical behaviour and thus the charge carriers in devices based on them can be effectively tuned by molecular engineering by either changing peripheral ligands or central metal atom. 13,14 For example, chemiresistors based on p-type transition metal MPc displayed unipolar carrier transport in redox gases sensing, depicting current increase under electron acceptor gases and current decrease under donor gases.…”

Tuning of interfacial charge transport in polyporphine/phthalocyanine heterojunctions by molecular geometry control for an efficient gas sensor

“…4d displayed a shift towards the lower binding energy as compared to ZnP monomer. It indicates that Highest Occupied Molecular Orbital (HOMO) level of the polymers moves upward closer to the Lowest Occupied Molecular Orbital (LUMO) level, narrowing the band gap after the polymerizations [26]. Moreover, the decrease in VBM is higher in pZnP-2 compared to pZnP-1, implying the larger upward shifts of the HOMO level.…”

“…In another approach, MPor can be combined to other organic semiconductors such as MPc in organic heterostructures to benefit from high interfacial conductivity. Recently, we investigated this approach in MSDI device configuration having a top layer of high conducting polyporphyrins (from nickel(II) 5,15-(diphenyl)porphyrin and nickel(II) 5,15-(dimesityl)porphyrin monomers) grown by Chemical Vapor Deposition (CVD) over a low conducting films of CuPc or Cu(F 16 Pc) [26]. These devices revealed large enhancement in thin film conductivity, at first by polymerization, with a further boost by the organic heterojunction effect as well as high sensitivity towards NH 3 (detection limit 228 ppb).…”