Search

Precise synthesis of graphene nanoribbons (GNRs) is of great interest to chemists and materials scientists because of their unique opto-electronic properties and potential applications in carbon-based nanoelectronics and spintronics. In addition to the tunable edge structure and width, introducing curvature in GNRs is a powerful structural feature for their chemi-physical property modification. Here, we report an efficient solution synthesis of the first pyrene-based GNR (PyGNR) with curved geometry via one-pot K-region oxidation and Scholl cyclization of its corresponding well-soluble tetrahydropyrene-based polyphenylene precursor. The efficient A2B2-type Suzuki polymerization and subsequent Scholl reaction furnishes up to 35 nm long curved GNRs bearing cove- and armchair-edges. The construction of model compound, as a cutout of PyGNR, from a tetrahydropyrene-based oligophenylene precursor proves the concept and efficiency of the one-pot K-region oxidation and Scholl cyclization, which is clearly revealed by single crystal X-ray diffraction analysis. The structure and optical properties of PyGNR are investigated by Raman, FT-IR, solid-state NMR and UV-Vis analysis with the support of DFT calculations. PyGNR shows the absorption maximum at 680 nm, exhibiting a narrow optical bandgap of 1.4 eV, qualifying as a low-bandgap GNR. Moreover, THz spectroscopy on PyGNR estimates its macroscopic charge mobility of 3.6 cm2/Vs, outperforming other curved GNRs reported via conventional Scholl reaction.

The photoisomerization of chromophores embedded in biological environments is of high importance for biomedical applications, but it is still challenging to define the photoisomerization mechanism both experimentally and computationally. We present here a computational study of the azobenzene molecule embedded in a DPPC lipid membrane, and assess the photoisomerization mechanism by means of the quantum mechanics/molecular mechanics surface hopping (QM/MM-SH) method. We observe that while the trans-to-cis isomerization is a slow process governed by a torsional mechanism due to the strong interaction with the environment, the cis-to-trans mechanism is completed in sub-ps time scale and is governed by a pedal-like mechanism in which both weaker interactions with the environment and a different geometry of the potential energy surface play a key role.

Graphene nanoribbons (GNRs) with atomically precise width and edge structures are a promising class of nanomaterials for optoelectronics, thanks to their semiconducting nature and high mobility of charge carriers. Understanding the fundamental static optical properties and ultrafast dynamics of charge carrier generation in GNRs is essential for optoelectronic applications. Combining THz spectroscopy and theoretical calculations, we report a strong exciton effect with binding energy up to 700 meV in liquid-phase-dispersed GNRs with a width of 1.7 nm and an optical bandgap of 1.6 eV, illustrating the intrinsically strong Coulomb interactions between photogenerated electrons and holes. By tracking the exciton dynamics, we reveal an ultrafast formation of excitons in GNRs with a long lifetime over 100 ps. Our results not only reveal fundamental aspects of excitons in GNRs (gigantic binding energy and ultrafast exciton formation etc.), but also highlight promising properties of GNRs for optoelectronic devices., Comment: 26 pages, 4 figures, 5 pages Supplementary Information

Graphene quantum dots (GQD) are interesting materials due to the confined sizes which allow to exploit their optoelectronic properties, especially when they interface with organic molecules through physisorption. In particular, when interfaces are formed, charge transfer (CT) processes can occur, in which electrons can flow either from the GQD to the absorbed molecule, or vice versa. These processes are accessible by modelling and computational analysis. Yet, the presence of different environments can strongly affect the outcome of such simulations which, in turn, can lead to wrong results if not taken into account. In the present multiscale study, we assess the sensibility of the computational approach and compute the CT, calculated at interfaces composed by GQD and amino-acene derivatives. The hole transfer is strongly affected by dynamic disorder and the nature of the environment, and imposes stringent descriptions of the modelled systems to ensure enhanced accuracy of the transfer of charges., Comment: 19 pages, 3 figures

A major bottleneck in the fabrication of efficient bio-organic nanoelectronic devices resides in the strong charge recombination that is present at the different interfaces forming the complex system. An efficient way to overcome this bottleneck is to add a self-assembled monolayer (SAM) of molecules between the biological material and the electrode that promotes an efficient direct electron transfer whilst minimising wasteful processes of charge recombination. In this work, the presence of a pyrene-nitrilotriacetic acid layer carrying different metal centers as SAM physisorbed on graphene is fully described by mean of electrochemical analysis, field emission scanning electron microscopy, photoelectrochemical characterisation and theoretical calculations. Our multidisciplinary study reveals that the metal center holds the key role for the efficient electron transfer at the interface. While Ni2+ is responsible for an electron transfer from SAM to graphene, Co2+ and Cu2+ force an opposite transfer, from graphene to SAM. Moreover, since Cu2+ inhibits the electron transfer due to a strong charge recombination, Co2+ seems the transition metal of choice for the efficient electron transfer., Comment: 28 pages, 7 figures

The widespread interest in phase recognition of lipid membranes has led to the use of different optical techniques to enable differentiation of healthy and not fully functional cells. In this work, we show how the combination of different (non)linear optical methods such as One Photon Absorption (OPA), Two Photon Absorption (TPA) and Second Harmonic Generation (SHG) as well as the study of the fluorescence decay time leads to an enhanced screening of membrane phases using a fluorescent dioctadecyltetramethylindocarbocyanine (DiD) probe. In the current study we consider the pure liquid disordered phases of DOPC (room temperature) and DPPC (323 K), the solid gel phase of DPPC (298 K), and the liquid ordered phase of a 2:1 binary mixture of Sphingomyelin and Cholesterol. By means of extensive hybrid quantum mechanics molecular mechanics calculations and based upon the (non) linear absorption of the embedded probes, it is found that DiD can be used to identify the lipid bilayer phase. The joint TPA and SHG as well as fluorescence analyses qualifies DiD as versatile probe for phase recognition. In particular, the SHG data obtained by means of HyperRayleigh Scattering and by Electric Field Induced Second Harmonic Generation reveal differences in polarization of the probe in the different environments. The TPA results finally confirm the particular location of the probe in between the polar head group region of the 2:1 SM:Chol mixture in the liquid ordered phase., Comment: 33 pages, 4 figures