Computational study of coronoid carbazole based Macrocycles: influence of isomerism.

Carbazole (Cz) units have been recognized as crucial conjugated cores in organic electronics due to their good electro- and photoactive properties, such as high hole-transporting mobilities, when compared to other heterocycles. On the other hand, conjugated macrocycles should be useful building blocks for the construction of 2D porous surface networks or 3D inclusion complexes among other supramolecular structures.2 One of the most interesting features of conjugated cyclic oligomers is that their electronic, structural, and optical properties can be tuned as a function of their interior and exterior domains. Therefore, a systematic study of conjugated macrocycles with well-defined diameters is of crucial importance to establish the structure-property relationships of these materials. For that purpose, we carried out a purely theoretical study of coronoid molecules based on three different indolocarbazoles (ICz) structural isomers (see Figure 1) as indolo[2,3-a]carbazole (23a-4MC), indolo[2,3-b]carbazole (23b-4MC) and indolo[3,2-b]carbazole (32b-4MC), which contain four indolecarbazole units (4MC). This work aims to identify new macrostructures with interesting electronic properties as well as to display the usefulness of the theoretical tools to advance knowledge in the organic electronics field. Overall, this investigation contributes to elucidating the electronic properties of coronoid macrocycles, guiding experimental chemists to produce new molecules with desirable properties.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Impact of the dicyanomethylene substitution position on the cyclophane macrocycle formation in carbazole-based biradicals

π-Conjugated biradical compounds, featuring unique unsaturated valences and radical centers in the ground state, are fundamentally important for understanding the nature of chemical bonds and have potential applications in material science. [1] Recently, it has been demonstrated that several -conjugated mono- and biradicals systems form long strain -bonds between two unpaired electrons resulting in macrocyclic or staircase oligomers or polymers by self-assembly processes. [2] Therefore, these materials are potential building blocks for dynamic covalent chemistry (DCC) since the aggregates can be formed or broken upon soft external stimuli. For instance, 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole biradical (p-Cz-alkyl in Figure 1) reversibly converts upon soft stimuli (temperature, pressure, light) to a cyclophane tetramer as a result from the formation (or bond cleavage) of long C-C single bonds.[3] Here, we present an experimental and theoretical study in order to investigate how the N-substitution and the change from para- to meta-dicyanomethylene substitution on carbazole-based biradicals affects their biradical character and thus, their tendency to act as useful motifs for DCC (see Figure 1).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

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

Formation of stimuli-responsive cyclophanes by self-assembly: the case of carbazole-based biradicals

Dynamic covalent bonds has recently received lot of attention because of their unique feature to become reversible under mild conditions.[1] In this context, π-conjugated biradical compounds has emerged as essential building blocks.[2] For instance, we have demonstrated that 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole biradical reversibly converts to a macrocycle cyclophane upon soft stimuli (temperature, pressure, light), showing strong chromic effects.[3] We now extent this study towards longer conjugated carbazole backbone (i.e., indolocarbazole shown in Figure 1), aiming at investigating how the elongation of the conjugated backbone impacts on the formation of stimuli-responsive cyclophanes. The self-assembly process is investigated both in solution and solid state by linking theory and experiments.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Carbazole-based Diradicals for Dynamic Covalent Chemistry

Dynamic covalent chemistry (DCC) is focused on the creation of structural scaffolds based on chemical components that interact through strong but reversible bonds. In fact, dynamic covalent bonds receive lot of attention because of their unique feature to become reversible under mild conditions.1 conjugated diradical compounds has emerged as essential building blocks in DCC.2 In this work, we will review our most recent works on the formation of stimuli-responsive cyclophanes by self-assembly of carbazole-based diradicals. To this end, we use a combined experimental and theoretical approach that links vibrational spectroscopy with DFT calculations. In this sense, it is interesting to note that we have recently demonstrated the potential of a para-substituted carbazole with terminal dicyanomethylene (DCM) groups to act as building blocks in DCC.3 This quinoid carbazole monomer transforms to a macrocycle cyclophane upon soft external stimuli (temperature, pressure, light), showing strong chromic features. In addition, we have also recently explored how the different DCM substitution position affects the interesting chromoactive properties of carbazole compounds.4 Finally, we are currently exploring the effect of the elongation of the carbazole backbone on the formation of stimuli-responsive cyclophanes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Cyclophane self-assembly from carbazole-based diradicals

The investigation of π-conjugated diradical compounds, featuring radical centers in the ground state, is key to understanding the nature of chemical bonds.[1] Occasionally, these systems can form long σ C-C bonds between two unpaired electrons resulting in macrocyclic or staircase oligomers or polymers by self-assembly processes. Furthermore, these new C-C bonds are longer than an ordinary bond between two sp3 carbon resulting in reversible dissociation/formation behavior between isolated radical species and cyclophane structures. Therefore, these materials are potential building blocks for dynamic covalent chemistry (DCC).[2] Hereinto, we present an experimental and theoretical study of carbazole and indolocarbazole-based diradicals (Figure 1) with dicyanomethylene (DCM) groups in different positions (para-DCM or meta-DCM) to identify new building blocks to obtain multi-responsive materials.[3-5] To this end, we investigated the dynamic interconversion between the isolated diradical and the cyclophane structures under external stimuli such as temperature, pressure and so on. Specifically, our main aim is to study how the DCM substitution and the elongation of the conjugated core affect the diradical character and to understand the connection between this parameter and the cyclophanes stability. In addition, we want to investigate if this transformation is reversible or not.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Tuning the Diradical Character of Indolocarbazoles: Impact of Structural Isomerism and Substitution Position

In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density functional theory (DFT), a spin-flip time-dependent DFT approach, and the multireference CASSCF/NEVPT2 method have been applied to correlate the diradical character with the energetic trends (i.e., singlet–triplet energy gaps). In addition, the nucleus-independent chemical shift together with ACID plots and Raman intensity calculations were used to strengthen the relationship between the diradical character and (anti)aromaticity. Our study reveals that the substitution pattern and structural isomerism represent a very effective way to tune the diradical properties in ICz-based systems with meta-substituted systems with a V-shaped structure displaying the largest diradical character. Thus, this work contributes to the elucidation of the challenging chemical reactivity and physical properties of diradicaloid systems, guiding experimental chemists to produce new molecules with desirable properties.Funding for open access charge: Univesidad de Málaga/CBUA

Multiresponsive chromic soft materials: formation of strongly coupled σ-dimers from IndoloCarbazole-based biradicaloids

Dynamic covalent chemistry is focused on the creation of structural scaffolds based on chemical components that interact through strong but reversible bonds. In fact, dynamic covalent bonds receive lot of attention because of their unique feature to become reversible under mild conditions.1 π-conjugated biradical compounds has emerged as essential building blocks in DCC (dynamic covalent chemistry).2 We have recently demonstrated the potential of a para-substituted carbazole with terminal dicyanomethylene groups to act as building blocks in DCC.3 In fact, this quinoid carbazole monomer transform to a macrocycle cyclophane upon soft external stimuli (temperature, pressure, light), showing strong chromic features. Here, we explore the effect of the elongation of the carbazole backbone on the formation of stimuli-responsive cyclophanes by self-assembly. To this end, we use a join experimental and theoretical approach that links vibrational spectroscopy (Raman and IR) with DFT calculationsUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Modelling the optical properties of Benzochalcogenodiazole-based Copolymers using Tuned Range-Separated Hybrid Functionals

Since the discovery of organic semiconductors, these systems have been deeply investigated and many strategies to module their optical and electronic properties have been established. In this sense, Donor-acceptor (D−A) approach to conjugated polymer design has become a widely used method for preparing conjugated polymers with narrow band gaps. This approach involves synthesizing a polymer with a delocalized π-electron system that comprises alternating electron-rich (donor) and electron-deficient (acceptor) repeat units. The combination of high-lying HOMO levels (residing on the donor units) and low-lying LUMO levels (residing on the acceptor units) results in an overall narrow band gap for the polymer. In this sense, poly(cyclopentadithiophene)benzothiadiazole is a D−A polymer for which power conversion efficiencies in solar cells of 5 6 % are reported. In this work, we use density functional theory (DFT) calculations to investigate the tuning of the electronic and structural properties of cyclopentadithiophene ben zochalcogenodiazole D−A polymers, wherein a single atom in the benzochalcogenodiazole unit is varied from sulfur to selenium to tellurium. Resonance Raman (RR) spectroscopy is also used to describe the nature of the electronic excitations. Improved prediction of the optical properties h as been obtained by using long range corrected functionals functionals, considering both tuned and default range separation parameters, aiming at predicting their optical and charge transport properties.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Caracterización de sistemas basados en carbazol con transformación reversible entre birradical aislado y σ-agregados

El desarrollo de la química de moléculas orgánicas π-conjugadas que tienen una capa de valencia que no está completamente llena, también conocidas como sistemas de capa abierta, ha atraído mucho interés en estos últimos años. Estos sistemas presentan gran ventaja para aplicaciones en espintrónica, electrónica orgánica u óptica no lineal, entre otros.[1] Sin embargo, los sistemas π-conjugados con carácter birradical suelen ser poco estables a temperatura ambiente. Por tanto, el diseño y caracterización de compuestos birradicales estables presenta hoy en día un gran interés.[2] En este trabajo, presentamos un estudio experimental y teórico, basado en espectroscopias Raman y UV-Vis-NIR junto con cálculos DFT, de un compuesto bicarbazol que presenta transformaciones termocrómicas y piezocrómicas reversibles entre una especie quinoide de capa cerrada y otra especie biradical de capa abierta que forma agregados mediante enlaces de tipo-σ.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec