Diradicals Produce Ambipolar Transistors: What and Why

organic conjugated diradicals have gaining interest in the recent times given their uses in different formats of electronic applications encompassing OFETs,1 non-linear optical dyes, chromophores for singlet fission in OPV,2 etc. Our recent interests have turned into the role of their open-shell structures and their impact in the stabilization of +1, -1 charges. Since the first studies in fused planar diradicals, we were fascinated by the fully reversible and almost perfect oxidation/reduction mirror-like shapes of their cyclic voltammetries (i.e., uncommon in the organic field, in Fig. 1).3 This aimed us to test the ambipolar charge transport character of diradicals in OFETs and discovered that some particular diradicals are able to transport both kind of charges, holes and electrons, with similar mobility, or balanced p-n mobility.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Polycyclic Hydrocarbons from [4n]Annulenes: Correlation versus Hybridization Forces in the Formation of Diradicaloids

The conceptual connections between [4n] Hückel antiaromaticity, disjoint orbitals, correlation energy, pro-aromaticity and diradical character for a variety of extended π-conjugated systems, including some salient recent examples of nanographenes and polycyclic aromatic radicals, are provided based on their [4n]annulene peripheries. The realization of such structure–property relationships has led to a beneficial pedagogic exercise establishing design guidelines for diradicaloids. The antiaromatic fingerprint of the [4n]annulene peripheries upon orbital interactions due to internal covalent connectors gives insights into the diradicaloid property of a diversity of π-conjugated molecules that have fascinated chemists recently.J.C. thanks MINECO/FEDER of the Spanish Government (PGC2018-098533-B-100, PID2021-127127NB−I00 and RED2018-102815-T) and the Junta de Andalucía (UMA18FEDERJA057). M.K. and M.M.H. acknowledge the NSF (CHE-2107820 to M.K., CHE-1954389 to M.M.H.) for financial support. We thank the anonymous reviewers for their helpful comments. Funding for open access charge: Universidad de Málaga / CBU

Cross-conjugated isothianaphthene quinoids: a versatile strategy for controlling electronic structures

The elucidation of new structure–property relationships in π-conjugated molecules bearing quinoidal moieties is of relevance because of their use in organic electronics applications and their traditional assimilation as models of doped conducting polymers. Quinoidal oligothiophenes are ground state electronic hybrids between closed-shell Kekulé quinoidal and open-shell aromatic diradicaloid forms. The prominent contribution of the diradical character in longer oligomers beyond thiophene 4-mers results in a low stability, thereby limiting the ability to tune their properties. Thus, the control of these quinoidal/aromatic contributions is an important prerequisite to develop long quinoidal oligothiophenes. To address this problem, a series of quinoidal pentathiophenes with benzene-annelated isothianaphthene units were designed and successfully synthesized as stable structures. Combined molecular spectroscopies and theoretical modelling indicated that cross-conjugation appears upon the introduction of multiple benzene-annelated units, and that the number and position of the benzene-annelated units have a significant influence on the quinoidal/aromatic/cross-conjugated electronic structures. The newly developed quinoidal pentathiophenes functioned as organic semiconducting materials in transistor and near infrared phototransistor devices. This study demonstrates that modification of the cross-conjugated quinoidal structure is a promising strategy for fine-tuning electronic structures in π-extended quinoidal systems, which could help us to understand unique π-electronic features and to develop novel organic electronic materials.This work was supported by JSPS KAKENHI (20H02814, 20K21224, 20H05841, 20KK0123, 19K15505, 20H04639, 20K15352, 21K05213, 20H00379, 20H05833, and 20K15261), CREST (J205101030), NEDO (21500248-0), and “Dynamic Alliance for Open Innovation Bridging Human, Environmental and Materials” from The Ministry of Education, Culture, Sports, Science and Technology, Japan. We are grateful to Prof. Toshihiro Ohnishi for helpful discussion. The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU and MINECO/FEDER of the Spanish Government (project PGC2018-098533-B-100), the Ministry of Science and Technology of the Spanish Government (project RED2018-102626-T) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga. // Funding for open access charge: Universidad de Málag

Oligoene and cyanine features of tetracyano quinoidal oligothiophenes

This paper interprets a palette of spectroscopic data on tetracyano thienoquinoidal molecules of different sizes oriented towards the elucidation of their electronic behavior and other aspects of interest in materials chemistry. It also provides a contextualization of these properties between those of even oligoenes (carotene-like) and those of odd cyanines as a function of the reduction state. A complete UV-Vis-NIR electronic absorption, fluorescence emission and infrared spectroscopic study in part helped by quantum chemical calculations in the framework of the DFT theory has been carried out. The study encompasses the neutral and charged states. The optical properties of these compounds in the neutral state are controlled by the competition of bright (electric dipole–dipole allowed) and dark (electric dipole–dipole forbidden) singlet excited states. In the anionic state, the trimeric compounds disclose behaviors compatible with being either charge localized or delocalized mixed valence systems. Interestingly, we show the π-dimerization of a radical anion of a thienoquinoidal compound forming a π-dimer dianion as a manifestation of the delocalization of the charge in the charged monomer. The hexamer compound in the neutral state discloses incipient diradical character which permits the detection of a NIR emission band from the dark state at energies well below 1 eV. As thiophene benzo-annulation minimizes the diradical character, it forces the confinement of the charge in the vicinity of the terminal dicyanomethylene groups in the dianion. The oxidized species of the compounds have been also analyzed as models of charge localization states. The competition between doublet and quartet high spin states in the radical cations has been explored with the objective of visualizing potential molecules able to produce SOMO–HOMO energy inversion. (...)The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU (PGC2018-098533-B-100 and RED2018-102815-T), and the Junta de Andalucı´a, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga

Triplet formation inhibits amplified spontaneous emission in perylene-based polycyclic aromatic hydrocarbons

Polycyclic Aromatic Hydrocarbons (PAHs) have demonstrated potential as active laser materials, showing good Amplified Stimulated Emission (ASE) properties. However, the molecular origin of their ASE properties is still unclear and depends on the particular compound. In this work we study the ASE properties of polystyrene films hosting three different perylene-based PAHs YZ-1, YZ-2 and YZ-3, where only YZ-3 has displayed ASE. Their molecular structure has been systematically changed to establish the connection between their molecular structure and their ASE properties. A complete spectroscopic study, with ground state and time-resolved techniques, show that, even at low yields, triplets play a critical role as a major loss mechanism. Their slow relaxation to ground state completely hinders the required unbalance of the S1 and S0 states for succesful ASE. Quantum chemical calculations suggest that a lower triplet density of states for YZ-3 is responsible for the blockage in triplet formation and, therefore, does not restrict ASE. This work not only presents a new PAH showing ASE, but also unequivocable proves the massive importance of triplet states in the development of organic lasers.JW acknowledges financial support from A*STAR AME grant (A20E5c0089). The group at the University of Alicante thanks financial support from the “Ministerio de Ciencia e Innovación” (MCIN) of Spain and the European Regional Development Fund (grant No. PID2020-119124RB-I00) and from the Generalitat Valenciana though grant No. AICO/2021/093. Besides, this study is part of the Advanced Materials program supported by the Spanish MCIN with funding from European Union Next Generation EU and by Generalitat Valenciana (grant no. MFA/2022/045). The group at the UA thanks Dr. J.M Villalvilla and Dr. J.A. Quintana for useful discussions. We also thank the Research Central Services (SCAI) of the University of Málaga for the access to the EVI, EEL and MENL to perform ground state and transient spectroscopic characterisation. JC thanks funding provided by MINECO/FEDER (PID2021-127127NB-I00, PID2019-110305GB-I00) and Junta de Andalucía (PROYEXCEL-0328)

Medium Diradical Character, Small Hole and Electron Reorganization Energies and Ambipolar Transistors in Difluorenoheteroles

Four difluorenoheteroleshavinga centralquinoidalcore with the heteroringvaryingas furan,thiophene,its dioxidederivativeand pyrrolehave shownto be mediumcharacterdiradicals.Solid-statestructures,optical,photophysical,magnetic,and electrochemicalpropertieshave been discussedin termsof diradicalcharacter,variationof aromaticcharacterand captoda-tive effects(electronaffinity).Organicfield-effecttran-sistors(OFETs)have been prepared,showingbalancedholeand electronmobilitiesof the orderof103cm2V1s1or ambipolarchargetransportwhichisfirst inferredfrom their redoxamphoterism.Quantumchemicalcalculationsshow that the electricalbehaviorisoriginatedfrom the mediumdiradicalcharacterwhichproducessimilarreorganizationenergiesfor hole andelectrontransports.The visionof a diradicalas simulta-neouslybearingpseudo-holeand pseudo-electronde-fects might justifythe reducedvaluesof reorganizationenergiesfor both regimes.Structure-functionrelation-ships betweendiradicaland ambipolarelectricalbehav-ior are revealed.The authorsthankthe SpanishMinistryof ScienceandInnovation(projectsMINECO/FEDERPGC2018-098533-B-100,and PID2019-110305GB-I00),the Junta de Andalucíaand GeneralidadValenciana,Spain (UMA18FEDERJA057,P18-FR-4549and Prometeo/2019/076)and JSPS KAKENHIgrant (JP21K05042for S.-i.K.,JP21K04995and JP21H05489for R.K., JP21H01887and JP20K21173for M.N.).S.-i.K.gratefullyacknowledgesthe AsahiGlassFoundationforfinancialsupport.We also thankthe ResearchCentralServices(SCAI)of the Universityof Málaga,UnidaddeEspectroscopíaVibracional(Dra. Capely Dr. Zafra)andUnidadde OpticaNo-Linealy EspectroscopíaUltrarápida(Dr. Román).This work was partiallysupportedby theCooperativeResearchProgram“NetworkJoint ResearchCenterfor Materialsand Devices”(KyushuUniversity).WethankProf. ShuheiHigashibayashi(KeioUniversity)forassistancewith synthesis.Mass spectrometricdata werecollectedat HiroshimaUniversity(N-BARD:Ms. TomokoAmimoto).Theoreticalcalculationswere partlyperformedusing ResearchCenterfor ComputationalScience(R-CCS),Okazaki,Japan.F.N and Y.D. acknowledgesupportfrom“Valutazionedella Ricercadi Ateneo”(VRA)—Universityof Bologna.Y.D. acknowledgesMinisterodell’Universitàedella Ricerca(MUR)for her Ph.D. fellowship. Funding for open access charge: Universidad de Málaga / CBU

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Efectos electrónicos y dinámicos de dirradicales orgánicos simétricos y asimétricos

La presente Tesis Doctoral está enfocada al estudio de las estructuras electrónicas y moleculares de sistemas orgánicos \pi-conjugados, en concreto de dirradicales Kekulé, así como de sus propiedades ópticas y electrónicas y su propuesta de uso potencial en dispositivos electrónicos orgánicos. Las moléculas elegidas tienen el patrón común de poseer una estructura quinoide o pro-aromática que las hace susceptibles de presentar un estado electrónico fundamental capa abierta con un carácter dirradical modulable por distintos componentes estructurales. Estos rasgos estructurales que modulan el carácter dirradical de los compuestos que a continuación se describen son: i) la flexibilidad del puente pi-conjugado, ii) el efecto del heteroátomo, iii) la asimetría de la interacción, iv) la longitud de cadena o v) la sustitución lateral de anillos bencenoides y la aparición de la cros-conjugación pi-electrónica. Para conseguir este propósito, las estructuras electrónicas y moleculares de cinco familias de sistemas diferentes han sido caracterizadas mediante espectroscopías ópticas y vibracionales y, siempre que ha sido posible, con técnicas de magnetoquímica como el SQUID o la resonancia espín-electrónica o paramagnética electrónica. En todos los casos los resultados obtenidos se han apoyado en cálculos químico-cuánticos. La investigación de estos sistemas se ha realizado atendiendo al diferente carácter dirradical que presentan las familias de sistemas objeto de estudio y, cuando ha sido pertinente, a su posible aplicabilidad

The heteroatom effect in ambipolar diradicals.

Contribución tipo Póster con Flash oralThe ability to efficiently transport both holes and electrons makes ambipolar organic materials appealing architectures in organic electronics for the development of p- and n-channel devices. However, most of the organic semiconductors do not exhibit ambipolar behaviour mainly due to their intrinsic electronic properties (energetic mismatch between their frontier molecular orbitals and the Fermi levels of the metals used as drain and source electrodes) and to charge trapping at OFET–gate dielectric interfaces. The search of new ambipolar materials is closely related to the examination of the redox amphoterism in π-conjugated structures, i.e., the capacity to equally accommodate positive and negative charges. In this context, the small HOMO-LUMO gap of π-conjugated molecules showing an incipient or medium diradical character makes them good candidates to display p–n balanced mobilities. Several open-shell molecules, such as a diindeno[b,i]anthracene derivative, zethrenes and diindenoperylenes, have been reported as efficient ambipolar materials indeed. In this communication we present a series of four difluorenoheteroles (DFX) with identical chemical structure except for the role of the heteroatom which is played by Oxygen, Nitrogen, Sulphur and Sulphur dioxide. The entire DFX series exhibit a medium diradical character as consequence of the combination of electronic affinity, captodative effect and aromatic stabilization. Addressing the electronic properties of the neutral, reduced and oxidized species of the DFX family we demonstrate their ambipolar electrical behaviour and elucidate the connection between their diradical character and the balance between the electron and hole transport.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Plant size, latitude, and phylogeny explain within-population variability in herbivory

Interactions between plants and herbivores are central in most ecosystems, but their strength is highly variable. The amount of variability within a system is thought to influence most aspects of plant-herbivore biology, from ecological stability to plant defense evolution. Our understanding of what influences variability, however, is limited by sparse data. We collected standardized surveys of herbivory for 503 plant species at 790 sites across 116° of latitude. With these data, we show that within-population variability in herbivory increases with latitude, decreases with plant size, and is phylogenetically structured. Differences in the magnitude of variability are thus central to how plant-herbivore biology varies across macroscale gradients. We argue that increased focus on interaction variability will advance understanding of patterns of life on Earth