Three Redox States of a Diradical Acceptor−Donor−Acceptor Triad: Gating the Magnetic Coupling and the Electron Delocalization

The diradical acceptor–donor–acceptor triad 1••, based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)–vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion, 1•–, and triradical cation species, 1•••+, obtained upon electrochemical reduction and oxidation, respectively, was monitored by optical and ESR spectroscopy. Interestingly, the modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes have been rationalized by theoretical calculations.This work was supported by the DGI grant (CTQ2013-40480- R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), and the Generalitat de Catalunya (grant 2014-SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496). M.S. is enrolled in the Material Science Ph.D. program of UAB and is grateful to MEC for a FPU predoctoral grant. S.V. and M.F. are thankful to the LabEx-Chemistry of Complex Systems for postdoctoral grants (ANR-10-LABX-0026CSC) and to the regional High-Performance Computing (HPC) center in Strasbourg for computational resources. We thank Amable Bernabé for the MALDI spectroscopy.Peer reviewe

Understanding the Influence of the Electronic Structure on the Crystal Structure of a TTF-PTM Radical Dyad

The understanding of the crystal structure of organic compounds, and its relationship to their physical properties, have become essential to design new advanced molecular materials. In this context, we present a computational study devoted to rationalize the different crystal packing displayed by two closely related organic systems based on the TTF-PTM dyad (TTF = tetrathiafulvalene, PTM = polychlorotriphenylmethane) with almost the same molecular structure but a different electronic one. The radical species (1), with an enhanced electronic donor–acceptor character, exhibits a herringbone packing, whereas the nonradical protonated analogue (2) is organized forming dimers. The stability of the possible polymorphs is analyzed in terms of the cohesion energy of the unit cell, intermolecular interactions between pairs, and molecular flexibility of the dyad molecules. It is observed that the higher electron delocalization in radical compound 1 has a direct influence on the geometry of the molecule, which seems to dictate its preferential crystal structure.This work was supported by the DGI grant (CTQ2013- 40480-R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), the EU ITN iSwitch 642196, the NANO2FUN Project No. 607721 and the Generalitat de Catalunya (grant 2014-SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015-0496). S.V. is thankful to the LabEx-Chemistry of Complex Systems for a post-doctoral grant (ANR-10-LABX-0026CSC) and to the regional High-Performance Computing (HPC) center in Strasbourg for computational resources. M.S. is enrolled in the Material Science Ph.D. program of UAB and is grateful to MEC for a FPU predoctoral grant.Peer reviewe

Synthesis and Characterization of Ethylenedithio-MPTTF-PTM Radical Dyad as a Potential Neutral Radical Conductor

During the last years there has been a high interest in the development of new purely-organic single-component conductors. Very recently, we have reported a new neutral radical conductor based on the perchlorotriphenylmethyl (PTM) radical moiety linked to a monopyrrolotetrathiafulvalene (MPTTF) unit by a π-conjugated bridge (1) that behaves as a semiconductor under high pressure. With the aim of developing a new material with improved conducting properties, we have designed and synthesized the radical dyad 2 which was functionalized with an ethylenedithio (EDT) group in order to improve the intermolecular interactions of the tetrathiafulvalene (TTF) subunits. The physical properties of the new radical dyad 2 were studied in detail in solution to further analyze its electronic structure.This work was supported by the EU ITN iSwitch 642196 and “Nano2Fun” 607721 DGI grant (BeWell; CTQ2013-40480-R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), and the Generalitat de Catalunya (grant 2014-SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496). In Denmark, this work was supported by the Danish Council for Independent Research | Natural Sciences (#11-106744). M.S. is grateful to Spanish Ministerio de Educación, Cultura y Deporte for a FPU grant. We thank Vega Lloveras for ESR spectroscopy and Amable Bernabé for MALDI spectroscopy.Peer reviewe

Multifunctional Materials based on TTFPTM dyads: towards new Molecular Switches, Conductors and Rectifiers

Esta Tesis está centrada en el diseño, síntesis y caracterización de nuevos materiales moleculares multifuncionales basados en sistemas Dador-Aceptor (D-A) formados por la unidad dadora de electrones tetratiafulvaleno (TTF) enlazada a la unidad aceptora de electrones el radical policlorotrifenilmetilo (PTM) mediante diferentes puentes -conjugados. Estos compuestos pueden exhibir propiedades físicas muy interesantes como biestabilidad o propiedades ópticas no lineales en solución, conductividad en estado sólido o rectificación cuando son anclados en superficies. Por tanto, estos sistemas podrían encontrar aplicación en el campo de la electrónica molecular como interruptores, conductores o rectificadores. En la primera parte de esta Tesis, se estudiará el fenómeno de biestabilidad en solución de un sistema D-A basado en un radical PTM conectado a un TTF mediante un puente vinileno. Este sistema puede exhibir un cambio inducido por la temperatura entre dímeros diamagnéticos a temperatura ambiente y monómeros paramagnéticos a alta temperatura. Los dos distintos estados presentan diferentes propiedades ópticas y magnéticas utilizando la temperatura como estímulo externo. Por otra parte, también se presentará el diradical A-D-A compuesto por dos subunidades PTM radicalarias conectadas mediante un puente TTF-vinileno que puede modificar reversiblemente sus propiedades ópticas, magnéticas y electrónicas al oxidarse o reducirse en solución. La modificación de la deslocalización electrónica y del acoplamiento magnético se observa cuando generamos las especies cargadas y los cambios han sido racionalizados mediante cálculos teóricos. En la segunda parte de la Tesis, se presentará la síntesis y caracterización de distintos derivados TTF--PTM incrementando el número de vinilenos entre las unidades D y A. También se estudiará la transferencia de carga intramolecular y las propiedades ópticas no lineales (NLO) en solución y su dependencia con la estructura electrónica abierta así como con la longitud del puente de cada uno de los compuestos. En la tercera parte de la Tesis, se estudiará las arquitecturas auto-ensambladas en estado sólido de un nuevo sistema TTF-PTM. La estructura cristalina muestra un ordenamiento supramolecular con una segregación de las unidades dadoras y aceptoras. Además, se estudiará la aparición de conductividad en los cristales del mismo sistema al aumentar la presión. El comportamiento de semiconductor a altas presiones se relacionará con el aumento de interacciones intermoleculares así como con el incremento de la deslocalización de carga. Finalmente, en la última parte de la Tesis se presentará un nuevo compuesto TTF-PTM que ha sido funcionalizado con un grupo disulfuro para preparar monocapas auto-ensambladas (SAMs) en superficies de oro. Estas SAMs han sido caracterizadas mediante diversas técnicas espectroscópicas para estudiar la estructura electrónica del sistema. Además, se estudiará el transporte de carga a través de las SAMs para evaluar un posible comportamiento de rectificación.This Thesis is focused on the design, synthesis and characterization of new multifunctional molecular materials based on donor-acceptor (D-A) dyads formed by the electron-donor tetrathiafulvalene (TTF) unit linked to the electron-acceptor polychlorotriphenylmethyl (PTM) radical moiety through different -conjugated bridges. These compounds can exhibit interesting physical properties such bistability and nonlinear optical properties in solution, conductivity in the solid state or electrical rectification when anchored on surfaces. Thus, these systems could find potential applications in the field of molecular electronics as switches, conductors or rectifiers. In the first part of the Thesis, we have studied the bistability phenomenon in solution of a D-A dyad based on a PTM radical linked to a TTF moiety through a vinyelene bridge. This system exhibited a temperature-induced switching between diamagnetic dimers at room temperature and paramagnetic monomers at high temperature. The two different states showed different optical and magnetic properties when using the temperature as external input. On the other hand, we have also reported the A-D-A diradical triad based on two PTM radical subunits connected through a TTF-vinylene bridge that can reversibly modify the optical, electronic and magnetic properties by one-electron reduction and oxidation in CH2Cl2 solution. The modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes were rationalized by theoretical calculations. In the second part of the Thesis, we have reported the synthesis and characterization of different TTF--PTM dyad derivatives increasing the number of vinylene units between the D and A moieties. We have studied the intramolecular charge transfer and non-linear optical (NLO) properties in solution and their dependence on the open-shell structure as well as on the bridge length for this family of compounds. In the third part of the Thesis, we have studied self-assembled architectures in the solid state of a new D-A dyad based on a PTM radical linked to a TTF moiety through a -phenyl-pyrrole bridge. The crystal structure showed an interesting supramolecular arrangement with segregated donor and acceptor units. Moreover, we reported the appearance of conductivity in single crystals of the same system when increasing the pressure. The semiconducting behavior at high pressures has been attributed to the enhanced intermolecular interactions and charge delocalization due to incorporation of TTF units which force the formation of close packed stacks of molecules. Finally in the last part of the Thesis, we have reported a new TTF-PTM dyad that was functionalized with a disulfide group in order to prepare self-assembled monolayers (SAMs) on gold. These SAMs were fully characterized by different spectroscopic techniques in order to study the electronic structure of the system. Moreover, charge transport measurements through the SAMs were performed in order to evaluate the possible rectification behavior

Multifunctional Materials based on TTFPTM dyads: towards new Molecular Switches, Conductors and Rectifiers

Esta Tesis está centrada en el diseño, síntesis y caracterización de nuevos materiales moleculares multifuncionales basados en sistemas Dador-Aceptor (D-A) formados por la unidad dadora de electrones tetratiafulvaleno (TTF) enlazada a la unidad aceptora de electrones el radical policlorotrifenilmetilo (PTM) mediante diferentes puentes -conjugados. Estos compuestos pueden exhibir propiedades físicas muy interesantes como biestabilidad o propiedades ópticas no lineales en solución, conductividad en estado sólido o rectificación cuando son anclados en superficies. Por tanto, estos sistemas podrían encontrar aplicación en el campo de la electrónica molecular como interruptores, conductores o rectificadores. En la primera parte de esta Tesis, se estudiará el fenómeno de biestabilidad en solución de un sistema D-A basado en un radical PTM conectado a un TTF mediante un puente vinileno. Este sistema puede exhibir un cambio inducido por la temperatura entre dímeros diamagnéticos a temperatura ambiente y monómeros paramagnéticos a alta temperatura. Los dos distintos estados presentan diferentes propiedades ópticas y magnéticas utilizando la temperatura como estímulo externo. Por otra parte, también se presentará el diradical A-D-A compuesto por dos subunidades PTM radicalarias conectadas mediante un puente TTF-vinileno que puede modificar reversiblemente sus propiedades ópticas, magnéticas y electrónicas al oxidarse o reducirse en solución. La modificación de la deslocalización electrónica y del acoplamiento magnético se observa cuando generamos las especies cargadas y los cambios han sido racionalizados mediante cálculos teóricos. En la segunda parte de la Tesis, se presentará la síntesis y caracterización de distintos derivados TTF--PTM incrementando el número de vinilenos entre las unidades D y A. También se estudiará la transferencia de carga intramolecular y las propiedades ópticas no lineales (NLO) en solución y su dependencia con la estructura electrónica abierta así como con la longitud del puente de cada uno de los compuestos. En la tercera parte de la Tesis, se estudiará las arquitecturas auto-ensambladas en estado sólido de un nuevo sistema TTF-PTM. La estructura cristalina muestra un ordenamiento supramolecular con una segregación de las unidades dadoras y aceptoras. Además, se estudiará la aparición de conductividad en los cristales del mismo sistema al aumentar la presión. El comportamiento de semiconductor a altas presiones se relacionará con el aumento de interacciones intermoleculares así como con el incremento de la deslocalización de carga. Finalmente, en la última parte de la Tesis se presentará un nuevo compuesto TTF-PTM que ha sido funcionalizado con un grupo disulfuro para preparar monocapas auto-ensambladas (SAMs) en superficies de oro. Estas SAMs han sido caracterizadas mediante diversas técnicas espectroscópicas para estudiar la estructura electrónica del sistema. Además, se estudiará el transporte de carga a través de las SAMs para evaluar un posible comportamiento de rectificación.This Thesis is focused on the design, synthesis and characterization of new multifunctional molecular materials based on donor-acceptor (D-A) dyads formed by the electron-donor tetrathiafulvalene (TTF) unit linked to the electron-acceptor polychlorotriphenylmethyl (PTM) radical moiety through different -conjugated bridges. These compounds can exhibit interesting physical properties such bistability and nonlinear optical properties in solution, conductivity in the solid state or electrical rectification when anchored on surfaces. Thus, these systems could find potential applications in the field of molecular electronics as switches, conductors or rectifiers. In the first part of the Thesis, we have studied the bistability phenomenon in solution of a D-A dyad based on a PTM radical linked to a TTF moiety through a vinyelene bridge. This system exhibited a temperature-induced switching between diamagnetic dimers at room temperature and paramagnetic monomers at high temperature. The two different states showed different optical and magnetic properties when using the temperature as external input. On the other hand, we have also reported the A-D-A diradical triad based on two PTM radical subunits connected through a TTF-vinylene bridge that can reversibly modify the optical, electronic and magnetic properties by one-electron reduction and oxidation in CH2Cl2 solution. The modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes were rationalized by theoretical calculations. In the second part of the Thesis, we have reported the synthesis and characterization of different TTF--PTM dyad derivatives increasing the number of vinylene units between the D and A moieties. We have studied the intramolecular charge transfer and non-linear optical (NLO) properties in solution and their dependence on the open-shell structure as well as on the bridge length for this family of compounds. In the third part of the Thesis, we have studied self-assembled architectures in the solid state of a new D-A dyad based on a PTM radical linked to a TTF moiety through a -phenyl-pyrrole bridge. The crystal structure showed an interesting supramolecular arrangement with segregated donor and acceptor units. Moreover, we reported the appearance of conductivity in single crystals of the same system when increasing the pressure. The semiconducting behavior at high pressures has been attributed to the enhanced intermolecular interactions and charge delocalization due to incorporation of TTF units which force the formation of close packed stacks of molecules. Finally in the last part of the Thesis, we have reported a new TTF-PTM dyad that was functionalized with a disulfide group in order to prepare self-assembled monolayers (SAMs) on gold. These SAMs were fully characterized by different spectroscopic techniques in order to study the electronic structure of the system. Moreover, charge transport measurements through the SAMs were performed in order to evaluate the possible rectification behavior

TTF–PTM dyads: from switched molecular self assembly in solution to radical conductors in solid state

Organic donor-acceptor (D-A) systems formed by the electron-donor tetrathiafulvalene (TTF) linked to the electron-acceptor polychlorotriphenylmethyl (PTM) radical through different π-conjugated bridges exhibit interesting physical properties such as bistability in solution or conductivity in solid state. Understanding the interplay between intra- and intermolecular charge transfer processes in solution is of high interest in order to rationalize the self-assembling ability and conducting properties of such dyads in solid state. In this Highlight we go over the self-assembling properties of different TTF-π-PTM radical dyads that find potential applications as molecular switches or conductors in the field of molecular electronics.This work was supported by the EU Training Networks (ITN) “iSwitch” (GA No. 642196) and ‘‘NANO2FUN’’ (GA No. 607721) DGI (Spain) grant (BeWell; CTQ2013-40480-R), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), and the Generalitat de Catalunya (grant 2014- SGR-17). ICMAB acknowledges support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015-0496). M. S. is grateful to Spanish Ministerio de Educación, Cultura y Deporte for a FPU grant and he is enrolled in the Material Science Ph.D. program of UAB.Peer reviewe

Multifunctional materials based on TTFPTM dyads : towards new molecular switches, conductors and rectifiers

Premi Extraordinari de Doctorat concedit pels programes de doctorat de la UAB per curs acadèmic 2017-2018Esta Tesis está centrada en el diseño, síntesis y caracterización de nuevos materiales moleculares multifuncionales basados en sistemas Dador-Aceptor (D-A) formados por la unidad dadora de electrones tetratiafulvaleno (TTF) enlazada a la unidad aceptora de electrones el radical policlorotrifenilmetilo (PTM) mediante diferentes puentes -conjugados. Estos compuestos pueden exhibir propiedades físicas muy interesantes como biestabilidad o propiedades ópticas no lineales en solución, conductividad en estado sólido o rectificación cuando son anclados en superficies. Por tanto, estos sistemas podrían encontrar aplicación en el campo de la electrónica molecular como interruptores, conductores o rectificadores. En la primera parte de esta Tesis, se estudiará el fenómeno de biestabilidad en solución de un sistema D-A basado en un radical PTM conectado a un TTF mediante un puente vinileno. Este sistema puede exhibir un cambio inducido por la temperatura entre dímeros diamagnéticos a temperatura ambiente y monómeros paramagnéticos a alta temperatura. Los dos distintos estados presentan diferentes propiedades ópticas y magnéticas utilizando la temperatura como estímulo externo. Por otra parte, también se presentará el diradical A-D-A compuesto por dos subunidades PTM radicalarias conectadas mediante un puente TTF-vinileno que puede modificar reversiblemente sus propiedades ópticas, magnéticas y electrónicas al oxidarse o reducirse en solución. La modificación de la deslocalización electrónica y del acoplamiento magnético se observa cuando generamos las especies cargadas y los cambios han sido racionalizados mediante cálculos teóricos. En la segunda parte de la Tesis, se presentará la síntesis y caracterización de distintos derivados TTF--PTM incrementando el número de vinilenos entre las unidades D y A. También se estudiará la transferencia de carga intramolecular y las propiedades ópticas no lineales (NLO) en solución y su dependencia con la estructura electrónica abierta así como con la longitud del puente de cada uno de los compuestos. En la tercera parte de la Tesis, se estudiará las arquitecturas auto-ensambladas en estado sólido de un nuevo sistema TTF-PTM. La estructura cristalina muestra un ordenamiento supramolecular con una segregación de las unidades dadoras y aceptoras. Además, se estudiará la aparición de conductividad en los cristales del mismo sistema al aumentar la presión. El comportamiento de semiconductor a altas presiones se relacionará con el aumento de interacciones intermoleculares así como con el incremento de la deslocalización de carga. Finalmente, en la última parte de la Tesis se presentará un nuevo compuesto TTF-PTM que ha sido funcionalizado con un grupo disulfuro para preparar monocapas auto-ensambladas (SAMs) en superficies de oro. Estas SAMs han sido caracterizadas mediante diversas técnicas espectroscópicas para estudiar la estructura electrónica del sistema. Además, se estudiará el transporte de carga a través de las SAMs para evaluar un posible comportamiento de rectificación.This Thesis is focused on the design, synthesis and characterization of new multifunctional molecular materials based on donor-acceptor (D-A) dyads formed by the electron-donor tetrathiafulvalene (TTF) unit linked to the electron-acceptor polychlorotriphenylmethyl (PTM) radical moiety through different -conjugated bridges. These compounds can exhibit interesting physical properties such bistability and nonlinear optical properties in solution, conductivity in the solid state or electrical rectification when anchored on surfaces. Thus, these systems could find potential applications in the field of molecular electronics as switches, conductors or rectifiers. In the first part of the Thesis, we have studied the bistability phenomenon in solution of a D-A dyad based on a PTM radical linked to a TTF moiety through a vinyelene bridge. This system exhibited a temperature-induced switching between diamagnetic dimers at room temperature and paramagnetic monomers at high temperature. The two different states showed different optical and magnetic properties when using the temperature as external input. On the other hand, we have also reported the A-D-A diradical triad based on two PTM radical subunits connected through a TTF-vinylene bridge that can reversibly modify the optical, electronic and magnetic properties by one-electron reduction and oxidation in CH2Cl2 solution. The modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes were rationalized by theoretical calculations. In the second part of the Thesis, we have reported the synthesis and characterization of different TTF--PTM dyad derivatives increasing the number of vinylene units between the D and A moieties. We have studied the intramolecular charge transfer and non-linear optical (NLO) properties in solution and their dependence on the open-shell structure as well as on the bridge length for this family of compounds. In the third part of the Thesis, we have studied self-assembled architectures in the solid state of a new D-A dyad based on a PTM radical linked to a TTF moiety through a -phenyl-pyrrole bridge. The crystal structure showed an interesting supramolecular arrangement with segregated donor and acceptor units. Moreover, we reported the appearance of conductivity in single crystals of the same system when increasing the pressure. The semiconducting behavior at high pressures has been attributed to the enhanced intermolecular interactions and charge delocalization due to incorporation of TTF units which force the formation of close packed stacks of molecules. Finally in the last part of the Thesis, we have reported a new TTF-PTM dyad that was functionalized with a disulfide group in order to prepare self-assembled monolayers (SAMs) on gold. These SAMs were fully characterized by different spectroscopic techniques in order to study the electronic structure of the system. Moreover, charge transport measurements through the SAMs were performed in order to evaluate the possible rectification behavior

Tetrathiafulvalene–Polychlorotriphenylmethyl Dyads: Influence of Bridge and Open-Shell Characteristics on Linear and Nonlinear Optical Properties

Three conjugated donor-π-acceptor radical systems (1 a–1 c) were prepared by bridging a tetrathiafulvalene (TTF) electron-donor unit to a polychlorotriphenylmethyl (PTM) electron-acceptor radical through vinylene units of different lengths. The dependence of the intramolecular charge transfer on the length of the conjugated bridge has been analyzed by different electrochemical and spectroscopic techniques. Linear optical properties and the second-order nonlinear optical (NLO) response of these derivatives have been computed by comparing systems 1 a–1 c with the non-radical analogues (2 a–2 c). Interestingly, an enhanced NLO response is predicted for dyads 1 a–1 c with PTM in the radical form and for compounds with longer vinylene bridges. Calculations confirm the active role the bridge plays for electronic communication between the donor TTF and the acceptor PTM units.This work was supported by the EU TrainingNetwork (ITN) “iS-witch” (GA No. 642196), the Spanish Ministry of EconomyandCompetitiveness MINECO (projects CTQ2013-40480-R andCTQ2015-71154-P), the Networking Research CenteronBioen-gineering, Biomaterials, and Nano- medici ne (CIBER-BBN), theGeneralitat de Catalunya (grant 2014-SGR-17), the Generalitat Valenciana (PROMETEO/2016/135) and European Feder funds(CTQ2015-71154-P). ICMAB acknowledges support from theMINECOthrough the “Severo Ochoa” Programme for Centresof Excellence in R&D (SEV-2015-0496). ICMol thanks theMINECOfor the Unidad de Excelencia Mar&adeMaeztu MDM-2015-0538. M.S. and J.C. are grateful to MECD of Spain for FPUpredoctoral grants.Wethank Amable Bernab8 for MALD Ispec-troscopy and Vega Lloveras for ESR spectroscopy.Peer reviewe

Conflicting evidence for ferroelectricity

D’Avino, Gabriele et al.Peer reviewe