•An amphiphilic perylenetetracarboxylic diimide derivative (APDI) is synthesized.•A novel LBL approach is developed to get the highly ordered APDI/CdS hybrid film.•CdS is incorporated into APDI matrix via H2S-vapor annealing over APDI/Cd2+ layer.•Energy transfer from CdS to APDI has been revealed in the unique hybrid film.An amphiphilic perylenetetracarboxylic diimide derivative (APDI) is designed and synthesized. The highly ordered APDI/CdS hybrid film was obtained successfully via a novel layer-by-layer approach by using a simple H2S-vapor annealing over each layer of APDI/Cd2+ Langmuir-Shäfer film fabricated from Langmuir monolayer of APDI molecules formed on the surface of CdCl2 aqueous solution. Examination by spectroscopic methods revealed APDI molecules in the hybrid film adopt a typical H aggregation mode whereas those in pure film adopt a slipped co-facial stacking mode in an “edge-on” conformation. The wurtzite CdS nanoparticles have been incorporated successfully into APDI matrix. The film morphology changed obviously from elongated domains of ca. 70 nm in length in pure APDI film to small nanoparticles of ca. 55 nm in diameter in APDI/CdS hybrid film. In particular, energy transfer from CdS to APDI has been established in the hybrid film.Highly ordered APDI/CdS hybrid film were successfully achieved via a novel layer-by-layer approach and an energy transfer from inorganic CdS to organic APDI is revealed.

Two novel amphiphilic porphyrin derivatives, 5-(benzo-(4-(2-(2-hydroxy)ethoxy)ethoxy))-10,15,20-triphenylporphyrinato zinc complex [ZnT(OC2H4OC2H4OH)PP] (1) and 5-(benzo-(4-(2-(4,10-N,N-15-crown-5)ethoxy)))-10,15,20-triphenylporphyrinato zinc complex [ZnT(OC2H4NN15C5)PP] (2), were designed, synthesized, and characterized by a range of spectroscopic methods. Their electrochemistry was studied by differential pulse voltammetry (DPV). Highly ordered films of 1 and 2 were fabricated by a solution-based quasi-Langmuir–Shäfer (QLS) technique, and were characterized by electronic absorption spectroscopy, IR spectroscopy, X-ray diffraction, atomic force microscopy (AFM) and current–voltage (I–V) measurements. Experimental results revealed that J-type aggregates are formed in the QLS film of 1 and 2. The crystallinity and general molecular order in the film of 1 were improved more effectively than in 2 due to its stronger intermolecular interactions. Furthermore, the conductivity of the QLS film of 1 was approximately 1 order of magnitude larger than that of 2. This indicates a significant effect of peripheral groups on the conducting behavior of porphyrins. In addition, the gas sensing behavior of the QLS films of 1 and 2 toward the electron acceptor gas, NO2, was investigated at concentrations 200 and 800 ppm, respectively. The sensitivity, stability, and reproducibility follow the order 1 > 2, revealing the effect of intermolecular interaction, film structure/morphology, and low-lying LUMO energy level on sensing performance. Unexpectedly, a decreased current response towards NO2 for the QLS films of both 1 and 2 was obtained for the first time, which unambiguously demonstrated the n-type semiconducting nature of 1 and 2. The present result represents not only the first example of n-type metalloporphyrin-based thin solid films obtained by a solution-based method, but more importantly provides an efficient way to enhance the performance of n-channel organic semiconductors through the combination of molecular design and the film fabrication technique.

Simple solvent vapor annealing over QLS film-based OFET devices fabricated from (Pc)Eu[Pc(ONh)8]Eu[Pc(ONh)8] led to a high and balanced ambipolar performance that has never been observed for small molecule single-component-based solution processed devices, with mobilities of 1.71 and 1.25 cm2 V−1 s−1 for holes and electrons, respectively, under ambient conditions.

Organic thin film transistor (OTFT) devices fabricated by the solution-based QLS technique from a mixed (phthalocyaninato)(porphyrinato) europium complex (TFPP)Eu[Pc(OPh)8]Eu[Pc(OPh)8] exhibit air-stable ambipolar performance with mobilities of 6.0 × 10–5 cm2 V−1 s−1 for holes and 1.4 × 10–4 cm2 V–1 s–1 for electrons, respectively. In good contrast, the two-component bilayer heterojunction thin film devices constructed by directly growing (TFPP)Eu[Pc(OPh)8]Eu[Pc(OPh)8] on vacuum deposited (VCD) CuPc film using solution based QLS method were revealed to show unprecedented ambipolar performance with carrier mobilities of 0.16 cm2 V–1 s–1 for holes and 0.30 cm2 V–1 s–1 for electrons. In addition to the intrinsic role of p-type organic semiconductor, the VCD CuPc film on the substrate also acts as a good template that induces significant improvement over the molecular ordering of triple-decker compound in the film. In particular, it results in the change in the aggregation mode of (TFPP)Eu[Pc(OPh)8]Eu[Pc(OPh)8] from J-type in the single-layer film to H-type in the bilayer film according to the UV–vis, XRD, and AFM observations.Keywords: ambipolar; organic heterojunction; OTFT; phthalocyanine; triple-decker

•A new sandwich-type bis(phthalocyaninato) europium complex was synthesized.•First example to fabricate flexible OFETs by a simple quasi–Langmuir–Shäfer method.•Good ambipolar transport for both holes and electrons has been obtained.A new sandwich-type bis(phthalocyaninato) europium complex [Pc(OAr)8]Eu[Pc(OAr)8] [Pc(OAr)8 = 2,3,9,10,16,17,23,24-octanaphthoxy phthalocyanine], was synthesized and fabricated into organic field-effect transistors devices on a flexible plastic substrate by using a simple solution-based quasi–Langmuir–Shäfer method. Ambipolar transport has been obtained in [Pc(OAr)8]Eu[Pc(OAr)8]-based thin film transistors with the carrier mobilities to 0.10 cm2 V−1 s−1 for holes and 0.01 cm2 V−1 s−1 for electrons, respectively. The energy levels of the highest occupied molecular orbital (−4.63 eV) and the lowest unoccupied molecular orbital (−3.41 eV) were obtained based on electrochemical studies of this double-decker complex. These values just simultaneously meet the energy levels required for p-type and n-type natures of organic semiconductors, suggesting the ambipolar organic semiconducting nature of this double-decker complex. Organized film microstructures and J-type molecular stacking mode for the double-decker complex in the quasi–Langmuir–Shäfer film are revealed. This study constitutes the first attempt to fabricate low-cost, flexible ambipolar phthalocyanine-based organic field-effect transistors by using simple solution-processing methods.Flexible, ambipolar OFETs based on the solution-processed QLS films of a new bis(phthalocyaninato) europium complex are obtained with the carrier mobilities of 0.10 cm2 V−1 s−1 for holes and 0.01 cm2 V−1 s−1 for electrons, respectively.

A novel amphiphilic heptafluorobutyl-substituted perylenetetracarboxylic diimide dimer, 1-amino-3,5-[N-amino-N′-heptafluorobutyl-1,6,7,12-tetra(tert-butylphenoxy)-3,4:9,10-perylene diimide]-2,4,6-triazine, has been synthesized. The self-assembly properties of this dimer in mixed tetrahydrofuran/water (THF–H2O) solvents of different volume ratios were studied. Fine-tuning of the non-covalent interactions of the amphiphilic molecules in 75/25, 50/50 and 25/75 THF/H2O v/v mixtures led to the formation of micro-flower clusters, micro-bowknots and nano-hollow spheres, respectively. The conductivity of the micro-bowknots was about one order of magnitude higher than the conductivity of the micro-flower clusters and the nano-hollow spheres. On saturation with hydrazine vapour, the conductivity was dramatically increased by about three, four and five orders of magnitude for the micro-bowknots, micro-flower clusters and nano-hollow spheres, respectively, compared with the aggregates in air. These results suggest new opportunities for the design and preparation of high-performance sensing devices using a combination of molecular design and controlled intermolecular interactions in mixed solvents.

•Two new (phthalocyaninato)(porphyrinato) europium complexes were synthesized.•The effect of side-group substituents on tuning the intermolecular stacking was revealed.•Triple-decker 1 in aggregates exhibited highly textured film structures.•A significantly enhanced conductivity was obtained from the aggregates of 1.Two new sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-decker (TDMAPP)Eu2[Pc(OPh)8]2 (1) and (TPyP)Eu2[Pc(OPh)8]2 (2) were designed and synthesized. The self-assembled aggregates of 1 and 2 were fabricated by means of a solution-based quasi-Langmuir–Shäfer (QLS) method. Both structures and properties of the aggregates of 1–2 were comparatively studied by UV–vis absorption spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) techniques and current–voltage (I–V) measurements. Experimental results indicated that the molecules of 1 in the self-assembled aggregates adopted a typical J-type (edge-to-edge) aggregation mode, whereas those of 2 took a “face-to-face” conformation and “edge-on” orientation, implying the effect of side-group substituents on tuning the intermolecular stacking. XRD and AFM characterization clearly showed evidence for the formation of highly textured film structures with controlled molecular orientations within the self-assembled aggregates of 1, while a dimeric supramolecular structure was revealed and thus as the building block self-assembles into the target the net-like nanostructures for the aggregates of 2. In addition, the highly ordered film of 1 showed good semiconducting property with a conductivity of ca. 2.35 × 10− 5 S·cm− 1, which is more than ca. 1 order of magnitude higher than those of 2, closely related to micro-structures and morphology found for the self-assembled aggregates.Two novel sandwich triple-deckers were synthesized, and fabricated into self-assembled aggregates by using a solution-based method. Comparative investigation results reveal that the substituent groups play a critical role on tuning the intermolecular stacking, and in turn impact on electrical conductivity of materials.

•A new amphiphilic, unsymmetrical 15C5PDI compound was synthesized.•Cation-induced aggregation from J-type into H-type was obtained.•Fluorescence emission change from “switch-on” to “switch-off” is observed.•Nanostructures formed at various air/liquid interface with different morphology.•A significantly enhanced conductivity was obtained from 1D nanofibrils of 15C5PDI.A novel amphiphilic perylenetetracarboxylic diimide (PDI) derivative, N-(4′-benzo-15-crown-5-ether)-N-hexyl-1,7-di(4-tert-butyl-phenoxy)perylen-3,4,9,10-tetracarboxylic diimide (15C5PDI), has been synthesized and characterized. Dimerization of 15C5PDI is induced in CHCl3 solution with the present of K+, resulting in the formation of the slipped co-facial J-aggregates, as revealed by absorption and fluorescence spectroscopies. Analysis of the surface pressure–area (π–A) isotherms and spectral change for the monolayer formed at the air/water interface, disclosed that 15C5PDI molecules adopted the H-type aggregation mode with a face-to-face configuration and edge-on orientation on both the surface of pure water and K+ aqueous solution. Consequently, a particularly interesting fluorescence emission change from “switch-on” to “switch-off” could be observed upon aggregation that was accompanied by a transformation from strongly fluorescent J-type into non-fluorescent H-type packing of the 15C5PDI dyes. Depending mainly on the coordination bonding between 15-crown-5-ether groups and K+ ions, one dimensional nanofibrils formed on the surface of the K+ aqueous solution with a more closely arrangement of 15C5PDI molecules relative to those on pure water subphase revealed by the π–A isotherms and atomic force microscopy (AFM) images. X-ray diffraction studies indicate that the film crystallinity and general molecular order in the Langmuir–Blodgett (LB) films deposited from the KCl solution are improved effectively in comparison with those from pure water subphase. Furthermore, the conductivity of the LB films prepared in K+ solution is more than ca. 1 order of magnitude higher than those from water.

The 2,3,9,10,16,17,24,25-octakis(phenoxy)phthalocyaninato zinc, (Zn[Pc(OPh)8]) was fabricated into nano-/micro-structures via solution-phase self-assembly. The self-assembling properties of Zn[Pc(OPh)8] in coordinating and non-coordinating solvents (methanol and n-hexane) have been comparatively studied by electronic absorption, fluorescence, Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due mainly to the presence of different intermolecular Zn–O coordination interactions between the Zn[Pc(OPh)8] molecules in n-hexane and between the Zn[Pc(OPh)8] and solvent molecules in methanol, the self-assembly of the Zn[Pc(OPh)8] results in nano-/micro-structures with distinctly different morphology as follows: nanobelts in n-hexane, and soft nano-sticks, microscale needle mushroom as well as pine leaves in methanol depending on aggregation time. The size and/or morphological evolution of the nanostructures have been clearly revealed during the self-assembly process. The present result appears to represent the first effort toward realization of controlling and tuning the biomorphs of self-assembled nanostructures of phthalocyanine-related complexes through the solvent coordinating effect. Furthermore, both nanobelts and micrometer-sized pine leaves were revealed to show good semiconductor features.

•A new class of liquid crystal quadruple-decker phthalocyanines.•Mono-oxidized phthalocyanine with ionic conductive nature is obtained.•High electric conductivity of 4.1 × 10−4 S cm−1 is achieved.Neutral and mono-oxidized states of novel sandwich-type tetrakis[2,3,9,10,16,17,23,24-octa(dodecanoyloxy)phthalocyaninato] terbium–cadmium quadruple-decker complex {[Pc(OC12H25)8]Tb[Pc(OC12H25)8]Cd[Pc(OC12H25)8]Tb[Pc(OC12H25)8]} (1) and {[Pc(OC12H25)8]Tb[Pc(OC12H25)8]Cd[Pc(OC12H25)8]Tb[Pc(OC12H25)8]}·SbCl6 (2) were synthesized and spectroscopically characterized. Polarized optical microscope (POM) together with differential scanning calorimeter (DSC) measurement revealed their similar two rectangular columnar mesophases over a relatively lower temperature range and higher temperature range, respectively, within their wide liquid crystal temperature range of 19–266 °C for 1 and 4–249 °C for 2. Temperature-dependent X-ray diffraction (XRD) analysis result disclosed the slight difference in terms of the neighboring quadruple-decker π–π stacking between these two mesophases, which in turn accounts for their electric conducting behavior along with the change in temperature. In addition, due to the ionic conductive nature, the mono-oxidized liquid crystals of 2 display more than 2 order of magnitude higher electric conductivity than that for 1, with the highest value 4.1 × 10−4 S cm−1 achieved at 140 °C.Graphical abstractThe mesophase of novel sandwich-type tetrakis[2,3,9,10,16,17,23,24-octa(dodecanoyloxy)phthalocyaninato] terbium–cadmium quadruple-decker compound in both neutral and mono-oxidized states with good semiconducting property has been revealed and clarified on the basis of polarized optical microscope, differential scanning calorimeter, and temperature-dependent X-ray diffraction analysis.

•A new sandwich mixed (phthalocyaninato) (porphyrinato) europium was synthesized.•The triple-decker has the good crystallinity and molecular order in the QLS film.•Highly balanced-mobility for hole and electron is obtained.A new sandwich mixed (phthalocyaninato) (porphyrinato) europium triple-decker (TPP)Eu2[Pc(OPh)8]2 (1), [TPP = dianion of 5,10,15,20-tetrakisporphyrin; Pc(OPh)8 = dianion of 2,3,9,10,16,17,23,24-octa(phenoxy)phthalocyanine], has been synthesized and characterized by a series of spectroscopic methods including MALDI-TOF mass spectrometry, 1H NMR spectroscopy, electronic absorption and infrared spectroscopy. The electrochemical property of 1 has been studied by cyclic voltammetry. Constructing the target triple-decker by coordination bonding between an europium ion and isoindole/tetrapyrrole nitrogen atoms from n-type double-decker (Eu[Pc(OPh)8]2) and p-type porphyrin (H2TPP) units, not only ensures the good solubility in conventional organic solvents, but more importantly successfully tunes the HOMO and LUMO levels into the range of ambipolar organic semiconductors required on the basis of electrochemical studies over 1. Using a solution-based quasi-Langmuir–Shäfer (QLS) method, the thin solid films of 1 were fabricated. The structure and properties of the thin films were investigated by UV–vis absorption spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Experimental results indicated the film crystallinity and general molecular order for (TPP)Eu2[Pc(OPh)8]2 molecules in the QLS films. Organic thin-film transistor (OTFT) fabricated from the QLS films of 1 was revealed to show ambipolar properties that have never been revealed for devices fabricated from a single-phthalocyanine/porphyrin mixed component using solution processable technique, with the highly balanced mobilities for holes and electrons of 0.04 cm2 V− 1 s− 1 and 0.08 cm2 V− 1 s− 1, respectively.

•A new class of ambipolar organic semiconductors for high performance OTFTs.•Solution-processed films of new triple-decker phthalocyanines were used as active layer.•Controlling of aggregation mode (H vs. J) for improving OTFT performance is achieved.•Air-stable electron and hole mobilities of 0.68 and 0.014 cm2/Vs were obtained.Two new tris(phthalocyaninato) europium complexes Eu2(Pc)[Pc(OPh)8]2 (1) and Eu2[Pc(OPh)8]3 (2) [Pc = unsubstituted phthalocyaninate; Pc(OPh)8 = 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninate], were designed and synthesized. Introduction of different number of electron-withdrawing phenoxy substituents at the phthalocyanine periphery within the triple-decker complexes not only ensures their good solubility in conventional organic solvents, but more importantly successfully tunes their HOMO and LUMO levels into the range of air-stable ambipolar organic semiconductor required on the basis of electrochemical studies over both 1 and 2, meanwhile fine controlling of aggregation mode (H vs. J) in solution-based film for improving OTFT performance is also achieved. Measurements over the OTFT devices fabricated from these sandwich compounds by a solution-based quasi–Langmuir–Shäfer (QLS) method reveal their ambipolar semiconductor nature associated with suitable HOMO and LUMO energy levels. Due to the H-aggregation mode employed by the heteroleptic triple-decker molecules in the QLS film, excellent performances with the electron and hole mobility in air as high as 0.68 and 0.014 cm2 V−1 s−1, respectively, have been revealed for the OTFT devices of heteroleptic triple-decker 1. This represents the best performance so far for solution-processable ambipolar single-component phthalocyanine-based OTFTs obtained under ambient conditions. In good contrast, homoleptic analogue 2 prefers to J-type aggregation and this results in relatively lower electron and hole mobility, around 0.041 and 0.0026 cm2 V−1 s−1 in air, respectively, for the devices fabricated. In particular, the performance of the devices fabricated based on 1 was found to remain almost unchanged in terms of both the carrier mobilities and on/off ratio even after being stored under ambient for 4 months.Graphical abstract

A high soluble dimeric perylene tetracarboxylic diimide (1) was fabricated into the thin solid films by means of quasi-Langmuir–Shäfer (QLS) method. The structure and properties of the QLS films were comparatively studied with those of monomeric perylene tetracarboxylic diimide (2) by electronic absorption, fluorescence, polarized electronic absorption spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). Experimental results revealed the film crystallinity and general molecular order in the film of 1 are improved effectively in comparison with those of 2 due to the dimeric structure of 1. Electron mobilities as high as 0.03 cm2 V−1 s−1 for the films of novel dimeric 1 are achieved, which is much better than that of monomeric 2 (5.0 × 10−7 cm2 V−1 s−1). In particular, the electronic mobility of 1 only slightly decreased after exposure to air and remained almost unchanged after 90 days, which is attributed to molecular packing effects including close stacking of dimeric PDI units and segregation effects imparted by the 2-N,N-di(n-butyl) amino-4,6-dihydrazine-1,3,5-trazine unites as well as relatively low-lying LUMO energy level. The present result represents not only the first example of solution-processed, air-stable dimeric PDI-based n-type OFET, but more importantly provides an efficient way to enhance the performance of air-stable n-channel organic semiconductors through intra-molecular bonding to pre-organizing the π-conjugated organic molecules into a rigid co-facially stacked structure.Graphical abstractHighlights► The first example of solution-processed, air-stable dimeric PDI-based n-type OTFTs. ► Dimeric 1 has the good crystallinity and molecular order in QLS film. ► Electron mobility as high as 0.03 cm2 V−1 s−1 for dimeric 1 is obtained.

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.

Two amphiphilic perylenetetracarboxylic diimide derivatives modified with different side chains at imide nitrogen, N-n-hexyl-N′-(2-hydroxyethyl)-1,7-di(4′-t-butyl)phenoxy-perylene-3,4:9,10-tetracarboxylic diimide (PDI 1) and N,N′-di(2-hydroxyethyl)-1,7-di(4′-t-butyl)phenoxy-perylene-3,4:9,10-tetracarboxylic diimide (PDI 2), were fabricated into organic nanostructures via solution-phase self-assembly. Their self-assembling properties in methanol and n-hexane have been comparatively studied by electronic absorption, fluorescence, and Fourier transform infrared spectroscopy (FT-IR). The morphologies and structures of the self-assemblies were examined by scanning electronic microscopy (SEM), atomic force microscopy (AFM), as well as X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due to the presence of different number of hydroxyethyl groups in the molecule of PDI 1 and PDI 2, the self-assembly of the two molecules in methanol and n-hexane results in nanostructures with distinctly different morphology as follows: nanobelts and nanoleaves for PDI 1 and nanobelt dendrites and nanosheets for PDI 2, respectively. Analysis of the spectral change for the aggregates relative to that of monomeric PDI in solution revealed that in polar and apolar solvents, both nanobelts and nanoleaves precipitated from PDI 1 adopt the H aggregation mode, whereas nanobelt dendrites and nanosheets from PDI 2 adopt H and J aggregation mode, respectively, implying the effect of both side-chain substituent and solvent on tuning the intermolecular stacking. Furthermore, the conductivity of the aggregates of either PDI 1 or PDI 2 from methanol is more than ca. 1 order of magnitude higher than those from n-hexane. In particular, the well-defined, one-dimensional (1D) nanobelts of PDI 1 show excellent semiconducting property with the electrical conductivity as high as 3.3 × 10−3 S cm−1, which might serve as promising candidates for applications in nano-electronics.Graphical abstractHighlights► PDI 1 and 2 were fabricated into organic nanostructures with different morphology. ► Excellent conductivities of the PDI aggregates from methanol are obtained. ► PDI 1 nanobelts exhibited an unexpected high conductivity of 3.3 × 10−3 S cm−1.

The solution-processed thin films of a series of three sandwich-type mixed (phthalocyaninato)(porphyrinato) europium complexes with different numbers of hydroxyl groups at the meso-substituted phenyl groups of porphyrin ligand 1–3 were prepared by a quasi-Langmuir–Shäfer (QLS) method. Examination by spectroscopic methods revealed that J-type aggregates have been formed with the increasing degree of order of molecular stacking 1 < 2 < 3 films. The IR and XRD results reveal that, a dimeric supramolecular structure was formed depending mainly on the π–π interaction between the tetrapyrrole cores of neighboring triple-decker molecules, which, as the building blocks, self-assembled into the target nanostructures through intermolecular hydrogen bonds. Competition and cooperation between the intermolecular π–π interaction and hydrogen bonding for different compounds were revealed to result in thin-film microstructure with a different morphology from nano-grains for 1 and 2 and nano-sheets for 3. An increasing sensitivity to NH3 at varied concentrations in the range of 15–800 ppm, follows the order 3 < 1 < 2, revealing the effect of film structure/morphology on sensing performance. In particular, excellent sensitivity, nearly complete reversibility and reproducibility to NH3 even at room temperature are obtained for the ultra-thin solution processed films from 2.

A series of unsymmetrical phthalocyaninato copper complexes simultaneously incorporating electron-withdrawing and electron-donating substituents at the phthalocyanine periphery Cu{Pc(15C5)[(COOC8H17)6]} (2), Cu{Pc[(adj-15C5)2][(COOC8H17)4]} (3), Cu{Pc[(opp-15C5)2][(COOC8H17)4]} (4), Cu{Pc(15C5)3[(COOC8H17)2]} (5) were prepared and isolated. For comparative studies, symmetrical analogues including 2,3,9,10,16,17,24,25-octakis(octyloxycarbonyl)phthalocyaninato copper complex Cu[Pc(COOC8H17)8] (1) and 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato copper complex Cu[Pc(15C5)4] (6) were also prepared. Their electrochemistry was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). With the help of a solution-based self-assembly process, these compounds were fabricated into organic field effect transistors (OFETs) with top contact configuration on hexamethyldisilazane (HMDS)-treated SiO2/Si substrate. In line with the electrochemical investigation results, a p-type OFET with a carrier mobility (for holes) of 0.06 cm2 V−1 s−1 was shown for Cu[Pc(15C5)4] (6) with electron-donating 15-crown-5 as the sole type of peripheral substituent. In contrast, n-type devices with a carrier mobility (for electrons) of 6.7 × 10−6–1.6 × 10−4 cm2 V−1 s−1 were achieved for 1–5 with electron-withdrawing octyloxycarbonyl substituents at the peripheral positions of phthalocyanine ring, indicating the significant effect of electron-withdrawing octyloxycarbonyl substituents on tuning the nature of phthalocyanine organic semiconductors. The present results represent the first example of solution-processed n-type phthalocyanine-based OFET devices.

A perylenetetracarboxylic diimide derivative, N-n-hexyl-N′-(2-hydroxyethyl)-1,7-di(4′-t-butyl)phenoxy-perylene-3,4:9,10-tetracarboxylic diimide (HO-PDI), was synthesized and self-assembled as a monolayer thin solid film on the modified surface of a quartz substrate by an ester bond between −OH groups of HO-PDI molecules and −COOH groups of p-phthalic acid grafted onto the hydrophilic pretreated SiO2 surface. An analysis of the spectral change revealed the J-aggregate nature of HO-PDI molecules in the obtained thin solid film. With this thin solid film of HO-PDI as a template, CdS nanoparticles were deposited on it in situ, which were further characterized by electronic absorption, fluorescence, and energy-dispersive X-ray spectroscopy (EDS). The morphology of CdS nanoparticles is disklike, and the diameter is ca. 140 nm as determined by atomic force microscopy (AFM). Furthermore, electron transfer between the organic layer and CdS nanoparticles was deduced through fluorescence quenching and theoretical analysis.

•A new soluble n-type phthalocyanine semiconductor (1) is synthesized.•The QLS film of 1 exhibits uniform nanoparticles with regular layered structure.•High crystallinity and good conductivity are revealed for the QLS film of 1.•High-sensitive room-temperature NO2 sensor based on the QLS film of 1 is developed.•The sensor offers detection of NO2 down to ppb levels with good stability.2(3),9(10),16(17),23(24)-tetrakis(2,2,2-trifluoroethoxy) phthalocyanine H2Pc(OCH2CF3)4(1) has been synthesized characterized by using MALDI-TOF MS, 1H NMR, UV–vis spectra and differential pulse voltammetry. Our work addresses this by introducing four electron-withdrawing trifluoroethoxy substituents at the periphery of the phthalocyanine ring to ensure the sufficient solubility and suitable LUMO energy level and thus successfully realize soluble n-type organic semiconductor. Furthermore, H2Pc(OCH2CF3)4 exhibited the high crystallinity and large specific surface area as well as good conductivity in the thin solid film fabricated by a simple solution-based quasi–Langmuir–Shäfer (QLS) method. Importantly, the highly sensitive, stable and reproducible responses to electron-accepting gas NO2 in 100–500 ppb range are observed for the QLS film of 1 at room temperature, implying the excellent potential of 1 as the NO2 sensor for applications in practical environments. In addition, the response of the QLS film of 1 is linearly correlated to the NO2 concentration. The interaction between the H2Pc(OCH2CF3)4 film and NO2 molecules with different concentrations was found to follow first-order kinetics. The present result represents not only the first example of n-type phthalocyanine-based NO2 sensor obtained by a solution-based method, but more importantly provides a new strategy for the molecular design to obtain soluble n-channel organic semiconductors in the field of sensing device fabrication.A new soluble n-type phthalocyanine semiconductor (1) is successfully synthesized by introducing four electron-withdrawing trifluoroethoxy substituents at the periphery of the phthalocyanine ring for optimizing molecular energy level. Highly sensitive, stable and reproducible responses to NO2 in 100–500 ppb range are observed for the solution-based QLS film of 1 at room temperature, depending on highly ordered film-structure, good crystallinity and conductivity of the QLS film of 1.

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.

A series of unsymmetrical phthalocyaninato copper complexes simultaneously incorporating electron-withdrawing and electron-donating substituents at the phthalocyanine periphery Cu{Pc(15C5)[(COOC8H17)6]} (2), Cu{Pc[(adj-15C5)2][(COOC8H17)4]} (3), Cu{Pc[(opp-15C5)2][(COOC8H17)4]} (4), Cu{Pc(15C5)3[(COOC8H17)2]} (5) were prepared and isolated. For comparative studies, symmetrical analogues including 2,3,9,10,16,17,24,25-octakis(octyloxycarbonyl)phthalocyaninato copper complex Cu[Pc(COOC8H17)8] (1) and 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato copper complex Cu[Pc(15C5)4] (6) were also prepared. Their electrochemistry was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). With the help of a solution-based self-assembly process, these compounds were fabricated into organic field effect transistors (OFETs) with top contact configuration on hexamethyldisilazane (HMDS)-treated SiO2/Si substrate. In line with the electrochemical investigation results, a p-type OFET with a carrier mobility (for holes) of 0.06 cm2 V−1 s−1 was shown for Cu[Pc(15C5)4] (6) with electron-donating 15-crown-5 as the sole type of peripheral substituent. In contrast, n-type devices with a carrier mobility (for electrons) of 6.7 × 10−6–1.6 × 10−4 cm2 V−1 s−1 were achieved for 1–5 with electron-withdrawing octyloxycarbonyl substituents at the peripheral positions of phthalocyanine ring, indicating the significant effect of electron-withdrawing octyloxycarbonyl substituents on tuning the nature of phthalocyanine organic semiconductors. The present results represent the first example of solution-processed n-type phthalocyanine-based OFET devices.

Simple solvent vapor annealing over QLS film-based OFET devices fabricated from (Pc)Eu[Pc(ONh)8]Eu[Pc(ONh)8] led to a high and balanced ambipolar performance that has never been observed for small molecule single-component-based solution processed devices, with mobilities of 1.71 and 1.25 cm2 V−1 s−1 for holes and electrons, respectively, under ambient conditions.