Unraveling the structure and dynamics of formation of covalent and non-covalent organic based 2D crystalline materials is key to control the quality of these materials, i.e. the defect density, and their size. These characteristics are important to understand and control their properties. In this contribution, our efforts on the use of scanning probe microscopy, and in particular scanning tunneling microscopy (STM), to visualize the structure and the dynamics of formation of substrate-supported metal organic frameworks (sMOF) and substrate-supported covalent organic frameworks (sCOF), at the liquid-solid interface, are highlighted.

It is shown that the quality of monolayer metal organic frameworks (MOF) depends critically on the solvent mixture. Moreover, using chiral solvents, homochiral lattices can be formed, in case of the metal containing supramolecular networks, while no chiral induction is observed in absence of the metal ion.

Covalent organic frameworks are formed based on boroxine chemistry. We report on a model boroxine 2D dynamic covalent polymer, and unveil both qualitative and quantitative details of the nucleation–elongation processes in real time and under ambient conditions. Sequential data analysis enable observation of the amorphous-to-crystalline transition, the time-dependent evolution of nuclei, the existence of ‘non-classical’ crystallization pathways and, importantly, the experimental determination of essential crystallization parameters with excellent accuracy, including critical nucleus size, nucleation rate and growth rate. In addition, we show that in specific cases, the electric field between the STM tip and the substrate can induce, on demand, the polymerization or depolymerization process.

We attained the synthesis of mesoscale ordered 2D polymers by the topochemical on-surface photopolymerization of fluorinated anthracene-triptycene (fantrip) monomers. The underlying protocol is two-staged: (1) Self-assembly of the monomers into a photopolymerizable monolayer structure, where the photoactive anthracene moieties are face-to-face stacked; (2) cross-linking of the self-assembled monolayer into a covalent 2D polymer by photochemically excited [4+4] cycloadditions between the antiparallel aligned anthracene blades. Thereby, the long-range order attained in (1) is transferred into the covalent state. Yet, the topochemical approach crucially depends on achieving the reactive packing with the appropriate mutual alignment of the anthracene blades. For the self-assembly the underlying surface plays a decisive role. We used graphite substrates, but additional passivation with an alkane monolayer was necessary to weaken molecule-surface interactions. As a result, the desired monolayer that is determined by molecule-molecule interactions became thermodynamically favored. STM has proven as ideal analytical tool for monitoring intermediate and final structures with the ultimate single-linkage resolution. The [4+4] cycloadditions induce a sizable increase of the HOMO-LUMO gap, which translates into an unambiguous change of STM contrast. This possibility to identify individual newly formed covalent linkages facilitated studies of the polymerization progression and allowed to assess the temperature dependence of polymerization rates, where an increase with temperature indicated a small energy barrier in the photoexcited state. In addition, successful photopolymerization could be corroborated by complementary local IR spectroscopy.

Covalent Organic Frameworks (COFs) are porous and ordered organic materials formed by condensation reactions of organic molecules. Recently, the Schiff-base chemistry or dynamic imine-chemistry has been explored for the synthesis of new COFs. The main reason for this tendency is the higher chemical stability, porosity, and crystallinity that they show in comparison to those previously reported, e.g. boronate ester-based COFs. The most typical imine-based COF structures are bidimensional and their synthesis can produce nanolayers or flakes of different lateral dimensions. This talk will summarize the most recent progress in preparing imine-based COFs that enable their processability. We will observe that the control of the COF-nanoparticle aggregation plays a fundamental role in the material processability. I will show some recent examples of 3D-printing of imine-based COFs and imine-based COF gels' formation and their transformation into aerogels and films to form functional centimeter-long membranes. Finally, I will provide some perspectives on the potential applications of these materials.

In the recent years, the synthesis of atomically precise framework materials such as metal-organic frameworks and covalent organic frameworks has resulted in first examples where the particular sub-class of two-dimensional (2D) polymers have both structural perfection and long-range crystalline order. Crystallinity imposes that lattice order effect emerge where properties, intrinsic to the lattice, reflect in the electronic and vibrational properties of the materials. 

I will highlight the importance of lattice effects on the chemical and physical properties of 2D polymers by starting from prototypical graphene towards materials with different underlying lattices, including honeycomb, square, kagome, and square-octagon lattices. Some of these lattices show correlated features such as flat bands and Dirac points, which result both in interesting physical phenomena, but are also opening the door for applications in catalysis. I will highlight the particular example of photocatalysis on honeycomb-kagome heterotriangulene 2D polymers and show how the interplay of molecular functionality and long-range order results in efficient metal-free non-toxic photocatalysts.

Nanographenes –polycyclic aromatic hydrocarbons that extend over 1 nm– can adopt a broad range of non-planar conformations that challenge the perception of aromatic systems as rigid and flat structures. Such distorted structures are the result of the steric strain induced by overcrowding or congestion in key positions of the aromatic core. Distorted nanographenes have shown enhanced solubility and unique optoelectronic and chiroptical properties as an effect of their distorted molecular structure. Our group has pioneered the introduction of distorted nanographenes in framework materials [1-5]. This merge offers new possibilities in the design monomers with symmetries that deviate from standard graphitic geometries, and in turn, in the design of organic frameworks with unprecedented architectures and properties. The most recent advances of these distorted framework materials including synthetic routes, optoelectronic properties, self-organising properties, and potential applications will be discussed.                                   

Synthetic two-dimensional polymers (2DPs) are an emerging class of structurally-defined crystalline materials that comprise covalent networks with topologically planar repeat units. Yet, synthesizing 2DP single crystals via irreversible reactions remains challenging. Herein, utilizing the surfactant-monolayer-assisted interfacial synthesis (SMAIS) method, few-layer, large-area, skeleton-charged 2DP (C2DP) single crystals were successfully synthesized through irreversible Katritzky reaction, under pH control. The resultant periodically ordered 2DPs comprise aromatic pyridinium cations and counter BF₄^- anions. The representative C2DP-Por crystals display a tunable thickness of 2-30 nm and a lateral size up to 120 μm². Using imaging and diffraction methods, a highly uniform square-patterned structure with the in-plane lattice of a = b = 30.5 Å was resolved with near-atomic precision. Significantly, the C2DP-Por crystals with cationic polymer skeleton and columnar-like pore arrays offer a high chloride ion selectivity with a coefficient up to 0.9, thus ensuring the integration as the anion-selective membrane for the osmotic energy generation. Our studies reveal a route to synthesize 2DP single crystals using a kinetically controlled irreversible reaction and will propel the development of membrane-based energy-conversion technologies.

We report on a novel concept for the production of two-dimensional organic nanoplateletts, which allows us to design the local surface chemistry. These nanoplateletts are polymer single crystals with a lamellar morphology.  Usually, these two-dimensional crystalline nanoplateletts have a homogeneous surface and structuring them is a major challenge. In this study we show the preparation of lamellar polymer crystals having a defined molecular thickness and in addition showing a core-rim architecture. The central area has a different chemical group on the surface than the peripheral area. We achieve this by sequential crystallization driven self assembly of precisely synthesized polymers with different functional groups in the main chain. We demonstrate the resulting structure of the nanoplateletts by means of fluorescent labeling and a selective chemical precipitation reaction at the hydroxyl groups located exclusively at the rim of the plateletts. The resulting polymeric two-dimensional platelets are obtained in a stable dispersion, which simplifies further processing and makes both crystal surfaces accessible for subsequent functionalization. A variety of polymers can be used, which keeps the process and the choice of surface functionalization very flexible. This new concept of designing surface chemistry thus opens up new possibilities in the field of nanotechnology.

Covalent organic frameworks (COFs) comprise an emerging class of materials based on the atomically precise organization of organic subunits into two- (2D) or three-dimensional (3D) porous crystalline structures connected by strong covalent bonds with predictable control over composition and topology.[1]

In our research group we are dealing with the synthesis of COFs based on imine[2] and/or imide linkages[3] by using both de novo synthesis and post-synthetic approaches.[4-9] We have addressed the issue of the  processability of COFs to get  suitable material dispersions. For this purpose,  liquid phase exfoliation (LPE) assisted by sonication and chemical exfoliation (CE) have shown to be easy and scalable methods to disrupt the non-covalent interactions between COF layers and produce COF nanosheets (CONs) suitable to be processable for different applications.We are especially interested in the development of photo and electroactive COFs for applications related with energy. In this communication we will comment on our previous results on 2D-COFs for charge storage and catalysis and  we will highlight our recent results on the development of COFs organic cathode materials with multiple redox sites (Figure) as efficient electrocatalysts for the oxygen reduction reaction (ORR).[10-14] 

Important benefits of these new COFs are that they are not only metal free, but also no additional
pyrolysis process has to be applied before its use. Instead, the electrocatalytic activity is a consequence of the specific electroactive
moieties selected for the design of the new COF electrocatalysts.

Quasi-two-dimensional conjugated polymers (q2DCPs) consist of 2D layered structures formed by the assembly of linear conjugated polymer chains via non-covalent bonds. They attracted increasing attention in recent years due to their outstanding physical properties, such as 2D coherent charge transport, high electrical conductivity, and significant enhancement of thermoelectric power factors. Polypyrrole (PPy) is one of the most studied linear conjugated polymers due to its unique optical and electrical properties associated with broad applications. However, it has remained largely unexplored to develop structurally defined PPy-based q2DCPs, referred to as quasi-two-dimensional polypyrrole (q2DPPy) due to challenges in synthesis, such as the helical conformation of PPy chain, side reaction and insufficient doping. In this work, we demonstrate the synthesis of novel q2DPPy films through oxidation polymerization of pyrrole on a concentrated sulphuric acid surface. Aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), grazing-incidence wide-angle X-ray scattering (GIWAXS) and density functional based tight-binding (DFTB) calculation indicate that the q2DPPy film is formed by layered assembly of protonated quinoidal chains with fully stretched conformation. The pyrrole unit of q2DPPy presents a fully cationic form compensated by HSO₄^- with a theoretically maximum doping level of n(HSO₄^-)/n(Py⁺) ≈ 1:1. This unique chain conformation and high doping level lead to a narrow bandgap and significant light absorbance of the q2DPPy film in the near-infrared (NIR) region. Remarkably, the resulting q2DPPy film displays record-high mobility of 31.68 cm²V^-1s^-1 by time-resolved terahertz spectroscopy (TRTS). We believe that this work is of general interest to a broad range of readers in 2D materials, conjugated polymer materials, supramolecular chemistry and physical science. We hope that you will share our excitement about the scientific breakthrough achieved in the present work.

The natural light-harvesting antennae of plants and photosynthetic bacteria are one of the most fascinating functional molecular nanoassemblies. Their unprecedented quantum efficiency relies on the strong coupling between thousands of densely packed chromophores giving rise to highly delocalized excitons which travels over long distances before reaching the reaction centre. However, the structural complexity of these systems leads to spectral congestion thereby blurring individual exciton transfer pathways that are vital to unravel for potential applications. Artificial model systems allow for better understanding of the structure-property relationship through reducing the complexity of natural light-harvesting complexes and disclosing the working principles to the basic elements.

Here we demonstrate a novel spectroscopic/microfluidics approach to deconvolute the supramolecular hierarchy and its connection to optical properties of a model system, multi-layered nanotubes [1-3]. They are based on the C8S3 molecules which self-assemble in an aqueous surrounding to a highly-ordered, concentric double-walled nanotubes (DWNTs) of 6/13 nm in inner/outer diameter and few micrometres in length. Each of these NTs can be considered as a quasi-2D molecular system (a plane wrapped into a tube) of strongly coupled molecules which results in highly delocalized and mobile excitonic states. We will presented a power platform of microfluidics, optical spectroscopy, and cryo-TEM, used to unravel the nature of exciton delocalization as well as exciton diffusion in DWNTs. We will also discuss the intermediate dynamical states of self-assembly via microfluidics manipulation of the structural hierarchy on the nanoscale via controlled alterations of individual sub-units of DWNT [4].

Graphene and other 2D materials are almost exclusively based on inorganic lattices. Except for the chemical functionalization of the surface of the 2D material, molecules have been scarcely considered in this area. Here I will illustrate the role of molecular magnetism in this area by selecting some relevant examples:

1) Molecular 2D magnets. I will focus on the design of molecular 2D magnets that, in contrast to what happens with the inorganic 2D magnets, are chemically stable in open air, keeping their magnetic properties preserved upon functionalizing their surface with different organic molecules [1].

2) Smart molecular/2D heterostructures. I propose to create hybrid heterostructures by interfacing stimuli-responsive molecular systems with graphene and semiconducting transition metal dichalcogenides (MoS2 and WSe2). The aim is that of tuning the properties of the “all surface” 2D material via an active control of the hybrid interface. This concept will provide an entire new class of smart molecular/2D heterostructures, which may be at the origin of a novel generation of hybrid materials and devices of direct application in highly topical fields like electronics, spintronics and straintronics. As smart-molecular systems I will choose magnetic spin-crossover materials able to switch between two spin states upon the application of an external stimulus (temperature, light or pressure) [2]. This spin transition is always accompanied by a significant change of volume in the material (by ca. 10%), so it can generate strain in its surroundings. I will show that in these heterostructures the electronic properties of graphene and the optical photoluminescence of monolayers of semiconducting metal dichalcogenides can be switched by light or by varying the temperature due to the strain concomitant to the spin transition [3, 4].

Molecular magnetism is an emerging field with potential for technological applications as high-density information storage, quantum computing and spintronics [1]. Molecular systems based on lanthanides are especially promising due to the fundamental properties of lanthanides. Their strong spin-orbit coupling can lead to a high magnetic anisotropy while the strong localization of 4f states reduces the hybridization with surfaces increasing spin lifetimes [2]. Both, a high anisotropy and a large spin lifetime, are essential to increase the magnetic stability and to develop practical applications. Some lanthanide molecular magnet systems have already been reported, as the double-decker phthalocyanine family (LnPc₂) [3,4], but up to now the magnetism of lanthanides metal-organic networks remains an unexplored field.

We performed pioneering investigations in this field preparing lanthanide-direct metal-organic networks using three molecular linkers: (i) benzene-1,4-dicarboxylic acid (TPA) coordinated with Dy on Cu(111) [5]; (ii) p-terphenyl-4,4-dicarboxylic acid (TDA) coordinated with Dy and Er on Cu(111) [5]; (iii) 4,4'-Di(4-pyridyl)biphenyl (DPBP) coordinated with Dy and Er on Au(111) [6]. The structural, electronic and magnetic properties were investigated by scanning probe microscopy (STM) and spectroscopy (STS), X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD). The experimental results were complemented by density functional theory (DFT) calculations and multiplet calculations. TPA and TDA linkers coordinate with lanthanides in almost square lattices with mononuclear metallic centers, and DPBP forms rhombic binuclear lattices. In both cases the network structure is preserved when the lanthanide atom is exchanged. However, the magnetic properties are drastically altered. The orientation of the easy axis of magnetization and the intensity of the magnetic anisotropy are strongly dependent on the metallic center and the molecular linker. Our results show that it is possible to tailor the magnetic properties of lanthanides by a proper choice of molecular linkers and metallic centers.

Two-dimensional covalent organic frameworks (2D COFs) are crystalline porous polymers characterized by long-range order and well-defined open nanochannels. 2D COFs are promising for applications in electronics, catalysis, sensing, and energy storage. The development of highly conductive 2D COFs has remained challenging due to the finite π-conjugation along the 2D lattice and defects introduced by grain boundaries. Furthermore, the charge transport mechanism within the crystalline framework has remained elusive. We use time- and frequency-resolved terahertz spectroscopy to reveal intrinsically Drude-type band transport of charge carriers in semiconducting 2D COF thin films condensed by 1,3,5-tris(4-aminophenyl)benzene (TPB) and 1,3,5-triformylbenzene (TFB). The TPB–TFB COF thin films demonstrate high photoconductivity with an exceptionally long charge scattering time exceeding 70 fs at room temperature which resembles crystalline inorganic materials. This corresponds to a record charge carrier mobility of 165 ± 10 cm2 V–1 s–1, vastly outperforming that of the state-of-the-art conductive COFs. These results reveal TPB–TFB COF thin films as promising candidates for organic electronics and catalysis and provide insights into the rational design of highly crystalline porous materials for efficient and long-range charge transport.

The basal plane of graphene is impermeable to all atoms and molecules - even for helium, the smallest - at ambient conditions [1]. Nevertheless, it is permeable to thermal protons [2]. This talk will provide an overview of our investigation of permeation of protons and other small ions through new 2D materials [3-5], including the unexpectedly fast ion exchange properties of atomically thin clays and micas [6].

References

[1]  Bunch, J. S. et al. Impermeable atomic membranes from graphene sheets. Nano Lett. (2008)

[2]  Hu, S. et al. Proton transport through one-atom-thick crystals. Nature (2014).

[3]  Mogg, L. et al. Atomically-thin micas as proton conduting membranes. Nat. Nano  (2019).

[4]  Mogg. L. et al. Perfect proton selectivity in ion transport through two-dimensional crystals. Nat. Commun. (2019).

[5]  Griffin, E. et al. Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects. ACS Nano (2020).

[6]  Y.-C. Zhou et al, Ion exchange in atomically thin clays and micas. Nat. Materials (2021).

In this work we introduce THz time-domain spectroscopy (THz-TDS) as a powerful non-contact tool for the characterization of the conductivity of metallic and semiconducting organic 2D crystalline materials. In a conventional THz-TDS experiment, a freely propagating ~1THz bandwidth reference pulse which is transmitted through air (or through a bare substrate transparent to THz radiation) is compared with a pulse transmitted through a self-standing sample (or a sample deposited onto the substrate). As the THz pulse is measured in the time domain, both, the amplitude and phase changes induced by the sample can be recorded; this enables retrieving the frequency-resolved complex conductivity. Modelling the later with electrical conduction models, allows accessing important key electric parameters as the averaged scattering rate and the plasma frequency from which, carrier density and charge carrier mobility could be inferred [1].

As a demonstration of the capabilities of THz-TDS, we present here several examples of studies of conductivity in 2D-based crystalline semiconducting and metallic MOF and COF materials. In a first example, we show how localization, induced by grain boundaries in polycrystals, modifies long-range charge transport in a semiconducting sample; as a second example we show how the interplane distance between 2D-MOF layers dramatically modifies the monitored conductivity. Finally, correlations between THz-TDS characterization and conventional 2- and 4-probe methods are highlighted.

Van der Waals heterostructures (vdWHs) provide the possibility of engineering new materials with emergent functionalities that are not accessible in another way. These heterostructures are formed by assembling layers of different materials used as building blocks. Beyond inorganic 2D crystals, layered molecular materials remain still rather unexplored, with only few examples regarding their isolation as atomically thin layers. Here, the family of van der Waals heterostructures is enlarged by introducing a molecular building block able to produce strain: the so-called spin-crossover (SCO). In these metal–organic materials, a spin transition can be induced by applying external stimuli like light, temperature, pressure, or an electric field. In particular, smart vdWHs are prepared in which the electronic and optical properties of the 2D material (graphene and WSe2) are clearly switched by the strain concomitant to the spin transition. These molecular/inorganic vdWHs represent the deterministic incorporation of bistable molecular layers with other 2D crystals of interest in the emergent fields of straintronics and band engineering in low-dimensional materials.

Ni₃(hexaiminotriphenylene)₂ aka Ni₃(HITP)₂ is a p-type semiconducting two-dimensional (2D) metal organic framework (MOF) analogous to graphene, with high ohmic conductivity of the order of ≈ 40 Scm^-1, as reported by Sheberla et al^[1]. Subsequently, a copper based conductive Cu₃(HITP)₂ was reported with potential application in gas sensing^[2]. Previous theoretical investigations indicate that these MOFs are metallic in bulk, whereas in their monolayers forms only Ni₃(HITP)₂ is semiconducting but with a narrow band gap^[3,4].  Herein, inspired by the Band Structure Engineering (BSE) deployed for OSCs and based on the recent advancements in truxene based semiconductors^[5-6], we consider different variants of Ni₃(hexaimidetriazatruxene)₂, Ni₃(HITAT)₂ aka MOF1, analogues to Ni₃(HITP). MOF1 is then functionalized by either: (i) substituting the ‘NH’ groups with sulfur atom^[5,6] resulting in Ni₃(HITTT)₂ aka MOF2, (ii) using truxenone as building block resulting in Ni₃(HITXN)₂ aka MOF3 and (iii) grafting cyano groups resulting in Ni₃(HITCT)₂ aka MOF4. The building blocks of these 2D-MOFs have been carefully selected as they can potentially improve the p-type transport, as expected in MOF2 when compared to MOF1, whereas the electron poor units in MOF3 and MOF4 should turn the MOFs into n-type materials^[7-8] while being prone to act as acceptors for metal-ion batteries. The role of molecular functionalization in these 2D-MOFs is discussed in terms of the variation in the bandwidths, bandgaps, in-plane effective masses, ionization potential and electron affinity.

Two-dimensional conjugated covalent organic frameworks (2D c-COFs) are emerging as a unique class of semiconducting 2D polymers for (opto-)electronics and energy devices. However, understanding the intricate interplay between the chemical structure and charge transport remains a challenge.^[1,2] We have demonstrated two metal−phthalocyanine-based pyrazine-linked 2D c-COFs (termed as MPc-pz COF, M = Cu or Zn) as p-type semiconductors with a band gap of ∼1.2 eV and intrinsic charge mobility up to ∼5 cm²/(Vs).^[3] The combination of Hall effect measurements, Terahertz spectroscopy, and density functional theory calculated electronic band structures provide a rational approach on how to assess structure-/doping-electronic property relationships.^[2,3] The results reveal that varying metal center from Cu to Zn has a negligible effect on the charge transport behaviors. After reversible p-type doping with I₂, the doping-defined 2D c-COF displays enhanced conductivity by 3 orders of magnitude, due to the elevated carrier concentration.^[4] Remarkably, charge mobility also increased upon doping, which can be traced to increased scattering time for free charge carriers, indicating that scattering mechanisms limiting the mobility are mitigated by doping. These works provide a guideline on how to assess the structure-electronic property relationships in 2D c-COFs semiconductors and highlight their potential in organic (opto-)electronic devices.

Magnetic two-dimensional (2D) materials have emerged recently with examples of inorganic monolayers, like CrI₃ [1] or CrSBr [2].

In this work,[3-5] we explore the magnetic properties of new 2D metal-organic frameworks (MOFs). In particular, we take advantage of layered molecular magnets since, thanks to the chemical design, it is feasible to bring new magnetic scenarios as well as to overcome the present instabilities of 2D magnetic materials. We develop a pre-synthetic method based on coordination chemistry that affords the isolation of crystalline molecular monolayers. The concept is illustrated using layered coordination polymers formed by reacting various benzimidazole derivatives with ferrocene. By the election of the proper ligand and the metal source, it is possible to tune the surface properties as well as the magnetism. Moreover, the magnetic order of the flakes is probed by its integration into membranes since phase transitions can be probed mechanically via the temperature-dependent resonance frequency and quality factor of the thin-membrane [6].

In addition, we recosnider the electrical characterization of the two-dimensional MOF M₃(THT)₂(NH₄)₃, (M = Fe, Ni, Cu, Co; THT, 2,3,6,7,10,11-triphenylenehexathiol),[7] observing that some claimed metallic phases[8] may be, indeed, higly insulating ones.

Overall, we detect the magnetic order in new magnetic 2D molecular materials and reconsider their electronic characterization. The results pave the way for studying phase transitions in the 2D limit in other metal-organic frameworks.
 

Two-dimensional conjugated polymers (2DCPs) have been described and recognised as crystalline, one- to two-layer polymer nanosheets prepared by 2D covalent polymerization exhibiting strong in-plane π-electron delocalization with two orthogonal directions and weak out-of-plane π-π stacking.[1,2] The extension of polymer dimensionality into two dimensions improves the alignment of individual polymer sheets and overcomes the limitations associated with charge carrier hopping between polymer chains in one-dimensional and crosslinked polymers.[3] Compared to other two-dimensional materials such as graphene or transition metal dichalcogenides, 2DCPs offer a high degree of flexibility in chemical design and are compatible with liquid-based processing methods. Various 2DCPs have been synthesised by surfactant monolayer-assisted interfacial synthesis (SMAIS).[5]

Of particular interest is the photoresponse of these materials due to their tunable properties, such as bandgap and associated wavelength-dependent photoexcitation, which enables a wide range of applications in optoelectronic devices. Using time-of-flight photoconductivity (TOF-PC) measurements [4], we investigate the charge transport properties of 2D polyacetylene prepared by SMAIS method. We preform TOF-PC measurement of 2D polyacetylene using a focused nanosecond pulse laser at 325 nm and electrode separation of 250 µm. From the bias polarity and time duration of the photocurrent, we can determine the polarity, velocity and mobility of photoexcited charge carriers as a function of applied bias voltage and excitation wavelength. Using excitation at 325 m, we observed an electron mobility in the range of 150 cm² V^-1 s^-1, which is in the realm of most advances small-molecule single-crystal organic semiconductors and almost an order of magnitude higher than linear polymeric semiconductors.