On the applicability of local softness and hardness

9 pages, 5 figures, 3 schemes, 2 tables.-- PMID: 20094672 [PubMed].Global hardness and softness and the associated hard/soft acid/base (HSAB) principle have been used to explain many experimental observed reactivity patterns and these concepts can be found in textbooks of general, inorganic, and organic chemistry. In addition, local versions of these reactivity indices and principles have been defined to describe the regioselectivity of systems. In a very recent article (Chem.–Eur. J. 2008, 14, 8652), the present authors have shown that the picture of these well-known descriptors is incomplete and that the understanding of these reactivity indices must be reinterpreted. In fact, the local softness and hardness contain the same potential information and they should be interpreted as the local abundance or concentration of their corresponding global properties. In this contribution, we analyze the implications of this new point of view for the applicability of these well-known descriptors when comparing two sites in three situations: two sites within one molecule, two sites in two different, but noninteracting molecules, and two sites in two different, but interacting, molecules. The implications on the HSAB principle are highlighted, leading to the discussion of the role of the electrostatic interaction.M. T. thanks the European Community for financial help through the postdoctoral grant MEIF-CT-2006-025362. P. G. and F. D. P are indebted to the Fund for Scientific Research—Flanders (FWO) and to the Free University of Brussels for continuous support to their group. P. W. A. thanks NSERC, the Canada Research Chairs, and Sharcnet for research support.Peer reviewe

Relations among several nuclear and electronic density functional reactivity indexes

A set of connections among several nuclear and electronic indexes of reactivity in the framework of the conceptual Density Functional Theory by using an expansion ofthe energy functional in terms of the total number of electrons and the normal coordinates within a canonical ensemble was derived. The relations obtained provided explicit links between important quantities related to the chemical reactivity of a system. This paper particularly demonstrates that the derivative of the electronic energy with respect to the external potential of a system in its equilibrium geometry was equal to the negative of the nuclear repulsion derivative with respect to the external potentia

Manipulating the fluorescence lifetime at the sub-cellular scale via photo-switchable barcoding

Fluorescent barcoding is a pivotal technique for the investigation of the microscale world, from information storage to the monitoring of dynamic biochemical processes. Using fluorescence lifetime as the readout modality offers more reproducible and quantitative outputs compared to conventional fluorescent barcoding, being independent of sample concentration and measurement methods. However, the use of fluorescence lifetime in this area has been limited by the lack of strategies that provide spatiotemporal manipulation of the coding process. In this study, we design a two-component photo-switchable nanogel that exhibits variable fluorescence lifetime upon photoisomerization-induced energy transfer processes through light irradiation. This remotely manipulated fluorescence lifetime property could be visually mapped using fluorescence lifetime imaging microscopy (FLIM), allowing selective storage and display of information at the microscale. Most importantly, the reversibility of this system further provides a strategy for minimizing the background influence in fluorescence lifetime imaging of live cells and sub-cellular organelles. Using fluorescence lifetime as the readout modality offers more reproducible and quantitative outputs compared to conventional fluorescent barcoding, being independent of sample concentration and measurement methods. Here, the authors design a photo-switchable nanogel exhibiting variable fluorescence lifetime, and demonstrate visual mapping by using fluorescence lifetime imaging microscopy on a sub-cellular scale.This work was supported by the ERC (grant number 615142), EPSRC, and the University of Birmingham, the Ministerio de Economia y Competitividad (MINECO) of Spain (project CTQ2016-80375-P) and the Basque Government (grant IT-324-07). The authors acknowledge the computational and technical and human support provided by DIPC. Y.X. acknowledges Chancellor's International Scholarship (University ofWarwick) for funding. All three reviewers are thanked for their time and contribution to the final version of this paper

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins.M.A. and I.C.R. wish to acknowledge the VUB for a Strategic Research Program awarded to ALGC. The resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by the Research Foundation - Flanders (FWO), and the Flemish Government. I.C.R. acknowledges co-funding from the European Union′s Horizon 2020 research and innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. It has been also supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), Gobierno Vasco (IT1346-19, IT1254-19, and PIBA19-0004), and the DIPC (DIPC_INV_003132). Open Access funding provided by University of Basque Country

Rational design of substituted maleimide dyes with tunable fluorescence and solvafluorochromism

We herein present a simple methodology to systematically expand the scope of maleimide-based dyes and also provide an insight into the relationship between substitution pattern and optical properties.</p

Angular momentum–induced delays in solid-state photoemission enhanced by intra-atomic interactions

Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe, the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models.This work was supported by the German Research Foundation (DFG) within the Collaborative Research Center (SFB) 613 (F.S., P.B., W.P., and U.H.), the Priority Programs SPP 1931 (C.S., M.H., and W.P.), and SPP 1840 (St.F., S.N., and W.P.); the Basque Government (grant IT-756-13 UPV/EHU) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.); and the Spanish Ministerio de Economía y Competitividad (grants FIS2016-76617-P and FIS2016-76471-P) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.) and Fondo Europeo de Desarrollo Regional (FEDER) (CTQ2016- 80375-P) (M.T.-S.). N.M.K. acknowledges hospitality and financial support from the theory group in cooperation with the small quantum systems (SQS) research group of European XFEL.Peer Reviewe

Desenvolupament, implementació i aplicació de noves metodologies per a l'estudi de la reactivitat química i de les propietats òptiques no lineals

El coneixement de la superfície d'energia potencial (PES) ha estat essencial en el món de la química teòrica per tal de discutir tant la reactivitat química com l'estructura i l'espectroscòpia molecular. En el camp de la reactivitat química es hem proposat continuar amb el desenvolupament de nova metodologia dins el marc de la teoria del funcional de la densitat conceptual. En particular aquesta tesis es centrarà en els següents punts:a) El nombre i la naturalesa dels seus punts estacionaris del PES poden sofrir canvis radicals modificant el nivell de càlcul utilitzats, de tal manera que per estar segurs de la seva naturalesa cal anar a nivells de càlcul molt elevats. La duresa és una mesura de la resistència d'un sistema químic a canviar la seva configuració electrònica, i segons el principi de màxima duresa on hi hagi un mínim o un màxim d'energia trobarem un màxim o un mínim de duresa, respectivament. A l'escollir tot un conjunt de reaccions problemàtiques des del punt de vista de presència de punts estacionaris erronis, hem observat que els perfils de duresa són més independents de la base i del mètode utilitzats, a més a més sempre presenten el perfil correcte. b) Hem desenvolupat noves expressions basades en les integracions dels kernels de duresa per tal de determinar la duresa global d'una molècula de manera més precisa que la utilitzada habitualment que està basada en el càlcul numèric de la derivada segona de l'energia respecte al número d'electrons.c) Hem estudiat la validesa del principis de màxima duresa i de mínima polaritzabiliat en les vibracions asimètriques en sistemes aromàtics. Hem trobat que per aquests sistemes alguns modes vibracionals incompleixen aquests principis i hem analitzat la relació d'aquest l'incompliment amb l'efecte de l'acoblament pseudo-Jahn-Teller. A més a més, hem postulat tot un conjunt de regles molt senzilles que ens permetien deduir si una molècula compliria o no aquests principis sense la realització de cap càlcul previ. Tota aquesta informació ha estat essencial per poder determinar exactament quines són les causes del compliment o l'incompliment del MHP i MPP.d) Finalment, hem realitzat una expansió de l'energia funcional en termes del nombre d'electrons i de les coordenades normals dintre del conjunt canònic. En la comparació d'aquesta expansió amb l'expansió de l'energia del nombre d'electrons i del potencial extern hem pogut recuperar d'una altra forma diferent tot un conjunt de relacions ja conegudes entre alguns coneguts descriptors de reactivitat del funcional de la densitat i en poden establir tot un conjunt de noves relacions i de nous descriptors.Dins del marc de les propietats moleculars es proposa generalitzar i millorar la metodologia pel càlcul de la contribució vibracional (Pvib) a les propietats òptiques no lineals (NLO). Tot i que la Pvib no s'ha tingut en compte en la majoria dels estudis teòrics publicats de les propietats NLO, recentment s'ha comprovat que la Pvib de diversos polímers orgànics amb altes propietats òptiques no lineals és fins i tot més gran que la contribució electrònica. Per tant, tenir en compte la Pvib és essencial en el disseny dels nous materials òptics no lineals utilitzats en el camp de la informàtica, les telecomunicacions i la tecnologia làser. Les principals línies d'aquesta tesis sobre aquest tema són:a) Hem calculat per primera vegada els termes d'alt ordre de Pvib de diversos polímers orgànics amb l'objectiu d'avaluar la seva importància i la convergència de les sèries de Taylor que defineixen aquestes contribucions vibracionals.b) Hem avaluat les contribucions electròniques i vibracionals per una sèrie de molècules orgàniques representatives utilitzant diferents metodologies, per tal de poder de determinar quina és la manera més senzilla per poder calcular les propietats NLO amb una precisió semiquantitativa.The knowledge of the potential energy surface (PES) has been essential in the world of the theoretical chemistry to discuss such as the chemistry reactivity as the molecular spectroscopy. In the reactivity chemistry we are interested to develop new methodology in the field of the conceptual functional density theory. This thesis will be center in the following points:a) The number and character of the different stationary points of the PES can have radical changes modifying the calculation level used. This fact produces that to be sure of the character of a stationary point is necessary to arrive a very precise calculation level. The hardness is a measure of the resistance of a chemistry system to change his electronic configuration, and taking into account the maximum hardness principle, where there is a minimum or a maximum of energy, there also is a minimum or a maximum of hardness, respectively. Choosing a set of problematic reactions in the number of stationary points, we noted that the hardness is more independent of the base and the method used and it always shows the correct shape.b) We made new expressions based in the integrations of the hardness kernel to predict the global hardness of a molecule in a more precise way that the numerical second derivative of the energy respect to the number of electrons.c) We studied the validity of the maximum hardness and the minimum polarizability principles in the asymmetric vibrations in aromatic systems. We found that for theses systems some vibrational modes break these principles and we studied the relationship of this non-fulfillment with the pseudo-Jahn-Teller effect. Moreover, we postulated a set of simple rules, that allows deducing if a molecule will follow or not these rules without a previous calculation. All this information has been essential to exactly determine the reasons of the fulfillment or non-fulfillment of the MHP and MPP.d) Finally, we made an expansion of the functional energy respect to the number of electrons and the normal coordinates into the canonic ensemble. The comparison of this expansion with the expansion of the energy respect to the number of electrons and the external potential give the recuperation of some know relations between traditional reactivity descriptors of DFT, but a different way, and establish a set of new relations and descriptors.In the field of molecular properties we propose to generalize and improve the methodology to calculate the vibrational contribution (Pvib) to the non-linear optical properties (NLO). Despite of that the Pvib is not taking account into the majority of the theoretical studies published of the properties NLO, it has recently been checked that the Pvib of different organic molecules with high NLO properties is bigger that the electronic contribution. Thus, the Pvib is essential to pattern new NLO materials used in informatics, telecommunications, and laser technology. The main lines of the research about this subject are:a) We have calculated for the first time the high terms of the Pvib for different organic polymer with the goal to evaluate the importance and the convergence of the Taylor series that define the vibrational contributions.b) We have evaluated the electronic and vibrational contributions for different representative organic molecules using different methodologies to predict the cheaper way to calculate the NLO properties with semi quantitative precision