Organic ambipolar semiconductors for TFT applications

In the last years we have devoted some effort to the search of new high-mobility semiconductors with ambipolar performances, good processability and environmental stability. Our approach, which is one of the most widely used, consists in the combination of donor and acceptor moieties in the conjugated skeleton, which allows fine tuning of the frontier molecular orbitals. For OTFT applications, low-lying HOMOs are essential to resist air oxidation and thus increase device stability. However, if the HOMO energy is too low, the resulting barrier to hole injection may compromise the transistor performance. Thus, a delicate balance between these two effects is needed. In particular, we have combined naphthaleneimide-derived moieties as electron accepting groups with electron-rich oligothiophene fragments. In these materials, we have found that the presence of ambipolar transport in these planar molecules can be understood on the basis of three interrelated properties: (i) the absence of skeletal distortions allows closer intermolecular pi-pi stacking and enhanced intramolecular pi-conjugation, (ii) increased pi-conjugation raises the HOMO energy, which approaches the Fermi level of common used electrodes; and (iii) more planar structures translate into lower Marcus reorganization energies. However, one of the limitations of these types of semiconductors is the presence of a molecular dipole moment, which forces the molecules to pack with pairwise intermolecular interactions orienting the naphthaleneimide cores in opposite directions, decreasing in some cases molecular orbitals overlapping. In recent contributions, we have devoted our efforts to analyze the effect of molecular interactions, through chemical modifications in order to induce parallel and antiparallel molecular packing, on the electronic properties of ambipolar semiconductors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Covalent organic frameworks based on Schiff-base chemistry: Synthesis, properties and potential applications

Covalent organic-frameworks (COFs) are an emerging class of porous and ordered materials formed by condensation reactions of organic molecules. Recently, the Schiff-base chemistry or dynamic imine-chemistry has been widely explored for the synthesis of COFs. The main reason for this new tendency is based on their high chemical stability, porosity and crystallinity in comparison to previously reported COFs. This critical review article summarizes the current state-of-the-art on the design principles and synthetic strategies toward COFs based on Schiff-base chemistry, collects and rationalizes their physicochemical properties, as well as aims to provide perspectives of potential applications which are at the forefront of research in materials scienceFinancial support from Spanish Government (Project MAT2014-52305-P and MAT2013-46753-C2-1-P) and a UCM-BSCH joint project (GR3/14) is acknowledge

Singular Temperatures Connected to Charge Transport Mechanism Transitions in Perylene Bisimides from Steady-State Photocurrent Measurements

Perylene bisimides (PBIs) are n-type semiconducting and photogenerating materials widely used in a variety of optoelectronic devices. Particularly interesting are PBIs that are simultaneously water-soluble and liquid-crystalline (PBI-W+LC) and, thus, attractive for the development of high-performing easily processable applications in biology and “green” organic electronics. In this work, singular temperatures connected to charge transport mechanism transitions in a PBI-W+LC derivative are determined with high accuracy by means of temperature-dependent photocurrent studies. These singular temperatures include not only the ones observed at 60 and 110 °C, corresponding to phase transition temperatures from crystalline to liquid-crystalline (LC) and from LC to the isotropic phase, respectively, as confirmed by differential scanning calorimetry (DSC), but also a transition at 45 °C, not observed by DSC. By analyzing the photocurrent dependence simultaneously on temperature and on light intensity, this transition is interpreted as a change from monomolecular to bimolecular recombination. These results might be useful for other semiconducting photogenerating materials, not necessarily PBIs or even organic semiconductors, which also show transport behavior changes at singular temperatures not connected with structural or phase transitions.We appreciate support from the Spanish government (MINECO) and the European Community (FEDER) through Grant MAT-2011-28167-C02-01, as well as the University of Alicante. We gratefully acknowledge financial support from MINECO (MAT2014-52305-P) and the UCM-BSCH joint project (GR3/14-910759). A. de la Peña thanks Universidad Complutense for a predoctoral fellowship

Gas–Solid Heterogeneous Postsynthetic Modification of Imine-Based Covalent Organic Frameworks

This is the peer-reviewed version of the following article: Martín-Illian, J. A., Royuela, S., Ramos, M. M., Segura, J. L., & Zamora, F. (2020). Gas‐Solid Heterogeneous Post‐Synthetic Modification of Imine‐based Covalent Organic Frameworks. Chemistry–A European Journal. 26 (29), 6495-6498, which has been published in final form at https://doi.org/10.1002/chem.202000224. This article may be used for non-commercial purposes in accordance with Wiley-VCH Terms and Conditions for Self-ArchivingThe copper-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction is among the most extensively used strategies for the post-polymerization modification of COFs. This work shows a new procedure for the postsynthetic functionalization of imine-based COFs by using a heterogeneous solid–gas reaction between alkyne-functionalized COFs and azides in the absence of a copper catalyst. This new alternative represents a step forward towards a greener postsynthetic modification of COFs opening a high potential for the development of new applicationsThis work was financially supported by MINECO (MAT2016‐77608‐C3‐1‐P and 2‐P

Electronic properties of Naphthalimide derivatives

Molecular systems have proven to be efficient active materials in electronics, making then suitable substitutes of the inorganic semiconductors used nowadays in electronic devices. For this reason, organic electronics has emerged as a research field with great potential and interest. In this project we have studied, both experimentally and theoretically, two ladder-type compounds functionalized with naphthalimides (Figure 1). The two molecular systems have been implemented in organic field effect transistors (OFETs), to assess their potential as active materials in organic electronics. Both compounds show p-type type mobility, moreover, NDI-TP-Ph-TP material also displays low n-type mobility, presenting a certain ambipolar character. The nature and stability of the charged species involved in the charge transport process have also been studied by spectroelectrochemical experiments.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Morphological, molecular and pathogenic characterization of Phytophthora palmivora isolates causing black pod rot of cacao in Colombia

Aim of study: To characterize isolates of Phytophthora sp. causing black pod rot (BPR) of cacao (Theobroma cacao L.).Area of study: Eight cocoa-growing regions in Colombia.Material and methods: Sixty isolates of Phytophthora sp. were obtained from tissues of cacao pods showing symptoms of BPR. Isolates were characterized using the morphology of sporangia and chlamydospores, molecular sequencing of regions of nuclear DNA (rDNA-ITS) and mitochondrial (COX) and virulence in different genotypes of cocoa pods.Main results: A high phenotypic variability between the isolates was determined, being the pedicel length and the length/width ratio (L/W) the most stable characters for species identification. Short pedicels with an average of 3.13 μm ± 0.28 and a length/width ratio of sporangia (L/W) with an average of 1.55 μm ± 0.11 were established as the most consistent morphological characteristics within palmivora species.Research highlights: Phytophthora pamivora was the only species associated to BPR, identified using morphology together with sequence analyses

Changes in retinal OCT and their correlations with neurological disability in early ALS patients, a follow-up study

Background: To compare early visual changes in amyotrophic lateral sclerosis (ALS) patients with healthy controls in a baseline exploration, to follow-up the patients after 6 months, and to correlate these visual changes with neurological disability. Methods: All patients underwent a comprehensive neurological and ophthalmological examination. A linear mixed analysis and Bonferroni p-value correction were performed, testing four comparisons as follows: Control baseline vs. control follow-up, control baseline vs. ALS baseline, control follow-up vs. ALS follow-up, and ALS baseline vs. ALS follow-up. Results: The mean time from the diagnosis was 10.80 +/- 5.5 months. The analysis of the optical coherence tomography (OCT) showed: (1) In ALS baseline vs. control baseline, a macular significantly increased thickness of the inner macular ring temporal and inferior areas; (2) in ALS follow-up vs. ALS baseline, a significant macular thinning in the inner and outer macular ring inferior areas; (3) in ALS follow-up vs. ALS baseline, a significant peripapillary retinal nerve fiber layer (pRNFL) thinning in the superior and inferior quadrants; and (4) ALS patients showed a moderate correlation between some OCT pRNFL parameters and Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) score. Conclusion: The OCT showed retinal changes in patients with motoneuron disease and could serve as a complementary tool for studying ALS

Electronic Properties of Naphthalimide-based Ladder-type Systems

The tuneable electronic and structural properties of organic semiconductors together with their flexibility, light weight, high solution processing and low costs in comparison with inorganic semiconductors are some of the key points for the current interest in the development of π-conjugated small molecules and polymers for a variety of applications. In this project, a combined experimental and theoretical study of two ladder-type compounds functionalized with naphthalimides1 (Figure 1) is performed with the aim to explore the impact of the structure on the optical and charge-transport properties. Compound NDI-TP-Ph-TP has an imidazole group as a spacer ring and NIP-TP-Ph-TP has a spacer ring of pyrazine type. The two molecular systems have been implemented in organic field effect transistors2 (OFETs), to assess their potential as active materials in organic electronics. Both compounds show p-type mobility, moreover, NDI-TP-Ph-TP material also displays low n-type mobility, presenting a certain ambipolar character.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech