Highly emissive supramolecular gold(I)-BTD materials.

Herein we report the synthesis of three light emitting rod-shaped gold(I) complexes by combining ethynyl-functionalized 2,1,3-benzothiadiazole (BTD), with different N-heterocyclic (imidazole, benzimidazole and phenantroimidazole) carbene gold(I) complexes. As could be determined by single crystal structure determination, the size of the N-heterocyclic carbene affects the relative disposition of the two ligands in the linear gold complexes (nearly perpendicular in the benzimidazole vs. planar in the phenantroimidazole derivative) which translates to different types of interactions between neighbouring units. In fact, the planar conformation in the more π-extended phenantroimidazole carbene allows Au(I) atoms to get sufficiently closer favouring aurophilic interactions. This compound is obtained as two different colour emitting solids which is ascribed to changes in packing modes probably leading to differences in the strength of aurophilic interactions. Interestingly, while the emission in the solid state is almost quenched, the incorporation of the compounds in polymer matrixes enhances the emissive properties of the compounds reaching near unity quantum yields.

Functionalized Crystalline N-Trimethyltriindoles: Counterintuitive Influence of Peripheral Substituents on Their Semiconducting Properties.

Three crystalline N-trimethyltriindoles endowed with different functionalities at 3, 8 and 13 positions (either unsubstituted or with three methoxy or three acetyl groups attached) are investigated, and clear correlations between the electronic nature of the substituents and their solid-state organization, electronic properties and semiconductor behavior are established. The three compounds give rise to similar columnar hexagonal crystalline structures; however, the insertion of electron-donor methoxy groups results in slightly shorter stacking distances when compared with the unsubstituted derivative, whereas the insertion of electron-withdrawing acetyl groups lowers the crystallinity of the system. Functionalization significantly affects hole mobilities with the triacetyl derivative showing the lowest mobility within the series in agreement with the lower degree of order. However, attaching three methoxy groups also results in lower hole mobility values in the OFETs (0.022 vs. 0.0014 cm2 V-1 s-1) in spite of the shorter stacking distances. This counterintuitive behavior has been explained with the help of DFT calculations performed to rationalize the interplay between the intramolecular and intermolecular properties, which point to lower transfer integrals in the trimethoxy derivative due to the HOMO wave function extension over the peripheral methoxy groups. The results of this study provide useful insights into how peripheral substituents influence the fundamental charge transport parameters of chemically modified triindole platforms of fundamental importance to design new derivatives with improved semiconducting performance.

The Effect of Auxiliary Nitrogenated Linkers on the Design of New Cadmium-Based Coordination Polymers as Sensors for the Detection of Explosive Materials.

Three new cadmium-based coordination polymers, denoted [Cd(hfipbb)(4,4'-bipy)] (CdPF-1), [Cd(hfipbb)(2,2'-bipy)] (CdPF-2), and [Cd(hfipbb)(1,10-phen)] (CdPF-3), have been hydrothermally synthesized by using the well-known V-shaped organic linker 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (H2 hfipbb), together with different nitrogenated auxiliary linkers. Considering the d10 configuration of the transition metal selected, the luminescent properties for these CdPF-n materials were explored, finding that materials CdPF-2 and CdPF-3 act as excellent sensors in the detection of explosive nitro aromatic compounds. The photoluminescence properties of CdPF-2 and CdPF-3 revealed that significant and sensitive fluorescence quenching was observed toward NP (nitrophenol) for CdPF-2 and PA (picric acid) for CdPF-3 in MeOH suspensions.

Untangling the Mechanochromic Properties of Benzothiadiazole-Based Luminescent Polymorphs through Supramolecular Organic Framework Topology.

Two new luminophore polymorphs of 4-bromo-7-(4-nonylphenyl)benzo[c][1,2,5]thiadiazole (1α and 1ß) exhibiting different color emissions, which switch into each other in response to shear force and solvent vapors, are presented and their X-ray structure is determined. Supramolecular organic framework topology (SOFT) studies on the two polymorphic structures led us to conclude that the mechanochromic phase transformation can be explained on the basis of modifications in their respective topological nets: mab and pcu for 1α and 1ß, respectively, as a result of the breaking and restoration of a number of weak supramolecular interactions. The color changes accompanying this transformation have been rationalized with the help of time-dependent density functional theory. We firmly believe that our findings will inspire future research on the design of novel stimuli-responsive organic materials with switchable properties based on their supramolecular interactions by establishing clear SOFT-property relationships.

Stimuli-Responsive Benzothiadiazole Derivative as a Dopant for Rewritable Polymer Blends.

A new rod-shaped benzothiadiazole fluorophore, namely, 4,7-di-(4-nonylphenyl)benzo[c][1,2,5]thiadiazole, which strongly emits fluorescence both in solution and in solid state has been synthesized, and its photophysical properties were rationalized with the help of density functional theory calculations. This molecule crystallizes in two distinct light-emitting crystalline phases, which can be interconverted in response to pressure, temperature, and solvent vapors. Powder X-ray diffraction indicates that in both polymorph, molecules adopt a lamellar packing, the different interlayer spacing being the main difference between the two structures. Single-crystal analysis of one of the polymorphs allows us to identify weak interaction planes, which presumably facilitates the polymorphic transformation through mechanically or thermally induced sliding processes. The polymorphic transformation and the origin of the switchable fluorescence have been rationalized through a spectroscopic and theoretical study. This study suggests that the different colors observed are due to different intermolecular aromatic interactions owing to the displacement of the molecules with respect to the layer normal. Interestingly, blending this molecule with a biodegradable polymer such as poly(vinyl alcohol) gives rise to a thermally activated reversible switchable fluorescent system, which entitles this material as an attractive candidate for technological applications, such as thermal sensors, security inks, or rewritable paper.

Using phosphine ligands with a biological role to modulate reactivity in novel platinum complexes.

Three platinum complexes with cis and trans configuration cis-[Pt(TCEP)2Cl2], cis-[Pt(tmTCEP)2Cl2] and trans-[Pt(TCEP)2Cl2], where TCEP is tris(2-carboxyethyl)phosphine, have been synthesized and fully characterized by usual techniques including single-crystal X-ray diffraction for trans-[Pt(TCEP)2Cl2] and cis-[Pt(tmTCEP)2Cl2]. Here, we also report on an esterification process of TCEP, which takes place in the presence of alcohols, leading to a platinum complex coordinated to an ester tmTCEP (2-methoxycarbonylethyl phosphine) ligand. The stability in solution of the three compounds and their interaction with biological models such as DNA (pBR322 and calf thymus DNA) and proteins (lysozyme and RNase) have also been studied.

Fluorescent and Electroactive Monoalkyl BTD-Based Liquid Crystals with Tunable Self-Assembling and Electronic Properties.

We report here on a series of redox active benzothiadiazole-based luminophores functionalized on one edge with a phenyl-nonyl substituent, which confers these molecules a rodlike shape and a tendency to self-assemble into layered superstructures. On the other edge, the molecules are endowed with different p-substituted phenyl rings, which allows the modulation of their redox and optical properties on the basis of the electronic nature of the terminal substituents. We have found that just one lateral alkyl chain is sufficient to induce mesomorphism in these molecules, which present nematic or smectic mesophases upon thermal treatment. Single-crystal analysis allows us to get an insight into the nature of the forces responsible for different supramolecular assemblies in these derivatives, and point to a strong contribution of the terminal groups in the different arrangements observed. The interesting redox and optical properties together with their self-assembling tendencies render these new materials interesting candidates for optoelectronics.