Theoretical study of Covalent Organic Frameworks based on C3-symmetric Central Cores

In recent years, the design and synthesis of COFs (covalent organic frameworks) has been deeply investigated. These materials are constructed from the union of different covalently linked conjugated platforms and they have a wide range of analytical applications, such as adsorption and / or separation of certain compounds, catalysis or identification of analytes, among others.1 On the other hand, the π-conjugated nature of these systems together with their extended 3D nature make them excellent candidates to be used in organic electronics.2 Recently, in collaboration with the group of Dr. Berta Gómez-Lor, we have studied the electronic and optical properties of four new porous truxene-based polymers.3 The results of this work opens the door to the control of the degree of π-conjugation and therefore to the optoelectronic properties of these materials (i.e., their potential as nitroaromatic compound sensors) through the substitution position of the truxene units. Here we propose to expand this study to COFs (Figure 1) derived from platforms with C3 symmetry based not only on truxene (X=C) but also on triindole (X=N) and truxenone (X=CO) units by means of periodic DFT-calculations (see Figure 1). Specifically, we study how the different structural modifications affect the intra- and intermolecular properties of the systems for their subsequent synthesis and real application in organic electronic devices.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Analyzing thin film morphology by Resonance Raman spectroscopy

Polymeric organic thin film transistors (OFETs) and all-polymer bulk heterojunction solar cells (all-PCS), which are composed of a polymer donor and a polymer acceptor, have attracted considerable attention in the last years. The interest of these polymeric materials present various advantages versus small molecular counterparts, including strong light absorption, excellent mechanical flexibility and durability, and great potential in printing applications due to their great processability. In OFETs and bulk heterojunction solar cells, the morphology and crystallinity control of the neat polymer or blended donor-acceptor polymer films is essential in order to improve device performance. In this communication, we present a Resonance Raman spectroscopy study directed to disentangle the film morphology of a series of all-acceptor and donor acceptor polymers for OFETs and all-PCS applications.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Triindoles as excellent platforms for organic semiconductors: from crystalline molecules to porous polymers

Organic semiconductors are one of the most promising candidates for next-generation electronics applications. In this sense, triindole-based systems have demonstrated great potential as p-type semiconductors in organic field-effect transistors (OFETs).1 In this project, a mixed experimental and theoretical study of three new crystalline N-trimethyltriindoles endowed with different functionalities at 3, 8 and 13 positions are investigated (Figure 1a), with the main goal of exploring the correlation between the electronic nature of the substituents and their solid-state organization and semiconductor behavior.2 On the other hand, the design and synthesis of covalent organic framework materials (constructed from the union of different covalently linked conjugated platforms) is being deeply investigated in organic electronic.3 Recently, in collaboration with the groups of Dr. Berta Gómez-Lor and Dr. Jose Ignacio Martínez, we have theoretically studied how the structural and the electronic properties of new porous triindole-based polymers (Figure 1b) can be modulated by the (i) modification of the linkage position from para (T2) to meta (T3), (ii) by the insertion of different π-bridges (phenylene or alkyne) between the cores and (iii) by the increment of the number of π-bridges from 3 to 6 units (T2,3).4Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Untangling the eclectronic propierties of triindole-based semiconductors

Organic semiconductors have emerged as an important class of materials that offer interesting prospects for high throughput, low-cost and flexible electronic circuits. In this sense, triindole-based systems have demonstrated great potential as p-type semiconductors in organic field-effect transistors (OFETs).[1] Recently, we have performed a combined experimental and theoretical study of three new crystalline N-trimethyltriindoles endowed with different functionalities at 3, 8 and 13 positions, either unsubstituted or with three methoxy or acetyl groups (Figure 1a), with the main goal of exploring the correlation between the electronic nature of the substituents and their solid-state organization, electronic properties and semiconductor behavior.[2] On the other hand, the design and synthesis of covalent organic framework materials (constructed from the union of different covalently linked conjugated platforms) are being deeply investigated in organic electronics.[3] In line with this , we have also investigated how the structural and the electronic properties of 2D triindole-based polymers (Figure 1b) can be modulated by the (i) modification of the linkage position from para (T2) to meta (T3), (ii) by the insertion of different π-bridges between the cores and (iii) by the increment of the number of π-bridges from 3 to 6 units (T2,3).[4] Overall, the results of this work open the door to the control of the degree of the π-conjugation for their subsequent synthesis and real application in organic electronic devices.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Untangling the electronic and charge transport properties of new Naphthalene and Perylene Diimides based-semiconductors

Organic semiconductors have emerged as an important class of materials that offer interesting prospects for high throughput, low-cost and flexible electronic circuits. Nevertheless, high performance electron-transporting (n-type) semiconductors are still rare compared to their high efficiency hole-transporting (p-type) counterparts. In this sense, the development of high-mobility and environmentally stable n-type materials for thin-film transistors has experienced a tremendous impetus in the last decade. Naphthalene-diimides (NDIs), perylene-diimides (PDIs) and their derivatives have demonstrated great potential as n-type semiconductors in Organic Field-Effect Transistors (OFETs). In this project, a mixed experimental and theoretical study of four new semiconductors (Figure 1) has been carried out with the aim to explore the impact of the following effects on the electronic and charge-transport properties: (i) the extension of the conjugated platform, going from a shorter conjugated core in naphthalene-diimides to a larger conjugated core in perylenediimides, (ii) the different donor units attached to the cores. For that, IR, UV-Vis absorption spectroscopy, and spectroelectrochemical measurements have been used in combination with theoretical calculations based on the Density Functional Theory (DFT). In addition, the four studied compounds have been implemented in OFETs , to assess their potential as active materials in organic electronics.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Analysis of morphologic effects of polymeric semiconducting materials by Raman spectroscopy.

The organic electronics research field has greatly advanced in the last decades, already rendering materials able to compete with their inorganic counterparts. However, the final blossoming of this field is expected to come with the complete understanding and control of the charge transport parameters in organic materials. In polymeric semiconductors, tuning the film morphology and crystallinity has been found to be crucial for efficient charge transport in devices. In this sense, planar backbones with locked conformations induced by intramolecular interactions are good candidates for high performing polymers. Thus, being able to elucidate both ordered and disordered phases in semiconducting films has been proven to be of great interest. Raman spectroscopy is a rapid, noninvasive technique able to gather information on molecular and supramolecular levels, thus being really useful for this purpose. In this communication, optical spectroscopies and, in particular Raman spectroscopy, are used to analyze the impact of the gradual fluorination on the electronic properties of donor-acceptor polymers, demonstrating that the final performance is highly dependent on the building blocks in with the fluorine atoms are introduced.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Improved prediction of the optical properties in pi-conjugated polymers: the case of benzochalcogenodiazole-based copolymers with different heteroatom substitution

Donor−acceptor (D−A) approach to conjugated polymer design has become a widely used method for preparing conjugated polymers with narrow band gaps.1 One outstanding D−A polymer is poly(cyclopentadithiophene)benzothiadiazole, PCPDTBT (P1 in Figure 1), for which power conversion efficiencies in solar cells of 4.5-5.5% are reported.2 In this work, we use resonance Raman (RR) and density functional theory (DFT) calculations to investigate the tuning of the electronic and structural properties of cyclopentadithiophene-benzochalcogenodiazole D−A polymers, wherein a single atom in the benzochalcogenodiazole unit is varied from sulfur to selenium to tellurium (Fig. 1).3 Sophisticated DFT calculations have been carried out using long-range corrected functionals, considering both tuned and default range-separation parameters, aiming at predicting their optical and charge transport properties. In addition, the nature of the electronic excitation is described by analyzing the enhancement pattern in the RR spectra using Raman excitation wavelengths coincident with the various transitions in the copolymers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Novel push-pull chromophores to prepare electro-optic modulators

In recent years, a large number of push-pull organic molecules have been proposed as promising candidates for electronic and optical applications. Generally, the main effort has been focused on the design of chromophores with large first hyperpolarizability values (β); this would result in a wide variety of nonlinear optical (NLO) applications, such as modulators.[1,2] In this work, we report an experimental and theoretical investigation of the NLO properties of novel push-pull systems derived from the dicyanomethylene-4H-chromene (DCM) group. Particular attention will be paid to better understand the molecular and electronic properties of these systems by using vibrational spectroscopic techniques and electrochemistry. Furthermore, these materials have been tested in a silicon-organic hybrid modulator based on an integrated dual-mode interferometer.[3]Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The fluorination effect: the importance of backbone planarity in achieving high performance ambipolar field effect transistors

We report here the synthesis and physico-chemical characterization of a series of donor–acceptor (D–A) copolymers consisting of 4,7-di(2-thienyl)-2,1,3-benzothiadiazole and isoindigo building blocks, which have been progressively fluorinated with the aim of enhancing intrachain interactions and thus increasing their electrical performances in organic field effect transistors (OFETs). The effect of the polymeric partially locked conformations, upon fluorination, on the material properties has been comprehensively analyzed by means of spectroscopic (UV-vis-NIR and Raman) and electrochemical techniques and density functional theory (DFT) calculations. Raman spectroscopy highlights that the impact of gradual fluorination on the molecular and electronic properties is highly dependent on the building blocks into which the fluorine atoms are introduced, being a much more efficient strategy to add them in the isoindigo unit. Electrical characterization of OFETs also shows that fluorination progressively increases the polymer coplanarity and electron affinity, varying the electrical performance from low hole dominated charge transport in the unfluorinated polymer to balanced ambipolar charge transport in the fluorinated ones. The best field-effect mobilities were recorded when fluorine atoms were added to the isoindigo unit, with values of 0.1 cm2 V−1 s−1 for both hole and electron transports.The work at the University of Málaga was supported by the MICINN (project PID2019-110305GB-I00) and by Junta de Andalucía (project P18-FR-4559). S. G.-V. thanks the MINECO for an FPU predoctoral fellowship (FPU17/04908). The authors would like to thank the computer resources, technical expertise and assistance provided by the SCBI (Supercomputing and Bioinformatics) centre of the University of Málaga. The Vibrational spectroscopy (EVI), XRD and AFM labs of the Research Central Services (SCAI) of the University of Málaga are also gratefully acknowledged. Al-Hashimi likes to acknowledge the financial support from the Qatar National Research Fund, Project Number NPRP12S-0304-190227. Notes and references // Funding for open access charge: Universidad de Málag

A Prato Tour on Carbon Nanotubes: Raman Insights

[EN] The functionalisation of carbon nanotubes has been instrumental in broadening its application field, allowing especially its use in biological studies. Although numerous covalent and non-covalent functionalisation methods have been described, the characterisation of the final materials has always been an added challenge. Among the various techniques available, Raman spectroscopy is one of the most widely used to determine the covalent functionalisation of these species. However, Raman spectroscopy is not a quantitative technique, and no studies are reported comparing its performance when the same number of functional groups are added but using completely different reactions. In this work, we have experimentally and theoretically studied the functionalisation of carbon nanotubes using two of the most commonly used reactions: 1,3-dipolar cycloaddition of azomethylene ylides and diazonium-based radical addition. The number of groups introduced onto the tubes by these reactions has been determined by different characterisation techniques. The results of this study support the idea that data obtained by Raman spectra are only helpful for comparing functionalisations produced using the same type of reaction. However, they should be carefully analysed when comparing functionalisations produced using different reaction types.The authors acknowledge financial support from the Spanish government (project PID2020-113080RB-I00) and the Junta de Comunidades de Castilla-La Mancha (project SBPLY/21/180501/000135/1). This study forms part of the Advanced Materials program and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by the Junta de Comunidades de Castilla-La Mancha. The work at the University of Malaga was funded by the MICINN (PID202-139548NB-I00) and by the Junta de Andalucia (P18-FR-4559) projects. The authors thankfully acknowledge the computer resources, technical expertise, and assistance provided by the SCBI (Supercomputing and Bioinformatics) centre of the University of Malaga. M. I. L. acknowledges her Juan de la Cierva Incorporacion grant (IJC 2018-035355-I) funded by MCIN/AEI/10.13039/501100011033. Funded with Aid for First Research Projects (PAID-06-22), Vice-rectorate for Research of the Universitat Politecnica de Valencia (UPV).Lucío, MI.; Giacalone, F.; La Parola, V.; Gámez-Valenzuela, S.; Muñoz-Alba, F.; Ruiz Delgado, MC.; Herrero, MA.... (2023). A Prato Tour on Carbon Nanotubes: Raman Insights. Chemistry - A European Journal. 29. https://doi.org/10.1002/chem.2023024762