Functionalized Zinc Porphyrins with Various Peripheral Groups for Interfacial Electron Injection Barrier Control in Organic Light Emitting Diodes

Carbon Nanodots as Electron Transport Materials in Organic Light Emitting Diodes and Solar Cells

Charge injection and transport interlayers play a crucial role in many classes of optoelectronics, including organic and perovskite ones. Here, we demonstrate the beneficial role of carbon nanodots, both pristine and nitrogen-functionalized, as electron transport materials in organic light emitting diodes (OLEDs) and organic solar cells (OSCs). Pristine (referred to as C-dots) and nitrogen-functionalized (referred to as NC-dots) carbon dots are systematically studied regarding their properties by using cyclic voltammetry, Fourier-transform infrared (FTIR) and UV-Vis absorption spectroscopy in order to reveal their energetic alignment and possible interaction with the organic semiconductor's emissive layer. Atomic force microscopy unravels the ultra-thin nature of the interlayers. They are next applied as interlayers between an Al metal cathode and a conventional green-yellow copolymer-in particular, (poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)], F8BT)-used as an emissive layer in fluorescent OLEDs. Electrical measurements indicate that both the C-dot- and NC-dot-based OLED devices present significant improvements in their current and luminescent characteristics, mainly due to a decrease in electron injection barrier. Both C-dots and NC-dots are also used as cathode interfacial layers in OSCs with an inverted architecture. An increase of nearly 10% in power conversion efficiency (PCE) for the devices using the C-dots and NC-dots compared to the reference one is achieved. The application of low-cost solution-processed materials in OLEDs and OSCs may contribute to their wide implementation in large-area applications.

Revealing the high-resolution structures and electronic properties of ZnTPP and its derivatives formed by thermally induced cyclodehydrogenation on Au(111)

Zinc(ii) tetraphenylporphyrin (ZnTPP) has very broad application prospects in the fields of supramolecular chemistry, solar cells and nanomaterials. In this paper, by using scanning tunneling microscopy (STM), we systematically investigated the ZnTPP molecule and its four derivatives formed by thermal annealing were characterized unambiguously by bond-resolved STM (BR-STM). The electronic properties of the ZnTPP molecule and its four cyclodehydrogenation products were investigated by scanning tunneling spectroscopy (STS) combined with DFT calculations. The spatial distribution of molecular frontier orbitals of four products was obtained by dI/dV mappings. This work gives rise to a full-scale investigation of ZnTPP on Au(111), which will be potentially useful in nanodevices and optoelectronics.

Ethyne Functionalized Meso-Phenothiazinyl-Phenyl-Porphyrins: Synthesis and Optical Properties of Free Base Versus Protonated Species

Synthesis, structural characterization and photophysical properties for a series of new trans-A2B2- and A3B-type ethynyl functionalized meso-phenothiazinyl-phenyl porphyrin derivatives are described. The new compounds displayed the characteristic porphyrin absorption spectra slightly modified by weak auxochromic effects of the substituents and fluorescence emission in the range of 651-659 nm with 11-25% quantum yields. The changes recorded in the UV-vis absorption spectra in the presence of trifluoroacetic acid (TFA) are consistent with the protonation of the two internal nitrogen atoms of the free-base porphyrin (19 nm bathochromic shift of the strong Soret band and one long wave absorption maxima situated in the range of 665-695 nm). Protonation of the phenothiazine substituents required increased amounts of TFA and produced a distinct hypsochromic shift of the long wave absorption maxima. The density functional theory (DFT) calculations of a porphyrin dication pointed out a saddle-distorted porphyrin ring as the ground-state geometry.

Dipolar Nanocars Based on a Porphyrin Backbone

The design and synthesis of a new family of nanocars is reported. To control their motion, we integrated a dipole which can be tuned thanks to strategic donor and acceptor substituents at the 5- and 15-positions of the porphyrin backbone. The two other meso positions are substituted with ethynyltriptycene moieties which are known to act as wheels. Full characterization of nine nanocars is presented as well as the electrochemistry of these push-pull molecules. DFT calculations allowed us to evaluate the magnitude of the dipoles and to understand the electrochemical behavior and how it is affected by the electron donating and accepting groups present. An X-ray crystal structure of one nanocar has also been obtained.