Multi-fold Sonogashira coupling: a new and convenient approach to obtain tetraalkynyl anthracenes with tunable photophysical properties

For the first time, a direct single-step one-pot route to access nine new symmetric tetraalkynylated anthracenes via Pd(CH₃CN)₂Cl₂/cataCXium®A catalyzed tetra-fold Sonogashira coupling is reported. Five of these tetraalkynylated anthracenes have been crystallographically characterized, with two of them exhibiting multiple interactions that significantly shorten the inter-planar distances in the solid-state structure. The rich photophysical properties exhibited by these molecules hold immense promise for future applications in sensors and optoelectronic devices. Two of the considered tetraalkynylated anthracenes comprising a D-π-A-π-D motif demonstrate solvatochromism and halochromism, with one of them showing a low bandgap of 1.79 eV. The remaining compounds demonstrate bandgaps in the range of 1.79-2.04 eV.

J-dimer emission in interwoven metal-organic frameworks

J-dimer emission is an emergent property that occurs when pairs of ground state fluorophores associate, typically in a dilute solution medium. The resulting fluorescence is shifted with respect to the monomer. J-dimer emission, however, has never been observed in concentrated dispersions or in the solid state. We posited that multivariate (MTV) MOFs with double interwoven structures would help to isolate these dimers within their crystalline matrix. Using this strategy, J-aggregate density was controlled during crystallization by following a substitutional solid solution approach. Here, we identified the presence of J-dimers over the entire composition range for interwoven PIZOF-2/NNU-28 structures with variable amounts of a diethynyl-anthracene aggregate-forming link. We produced bulk crystals that systematically shifted their fluorescence from green to red with lifetimes (up to 13 ns) and quantum yields (up to 76%) characteristic of π–π stacked aggregates. Photophysical studies also revealed an equilibrium constant of dimerization, K_D = 1.5 ± 0.3 M⁻¹, enabling the first thermodynamic quantification of link–link interactions that occur during MOF assembly. Our findings elucidate the role that supramolecular effects play during crystallization of MTV MOFs, opening pathways for the preparation of solid-state materials with solution-like properties by design.

J-dimer emission is an emergent property that occurs when pairs of ground-state fluorophores associate within multivariate MOFs producing tunable red shifted emission.

Nanocomposite approaches for enhancing the DC and photoconductivity of DNA films

Enhanced DC conductivity and photoconductivity of cationic carbazole tethered deoxyribonucleic acid (Cz-DNA) in film devices is achieved by incorporating mobility enhancers. An anthracene-based organic semiconductor (namely 4HPA-Ant) and the inorganic semiconductor cadmium sulfide (CdS) multipod nanocrystal (NC) were used as the mobility enhancers. Space charge limited current (SCLC) experiments show that hole mobility in CdS:Cz-DNA composite film is improved significantly, by about an order of magnitude, compared to the Cz-DNA film. Similarly, the DC conductivity of the composite film is slightly enhanced by 4HPA-Ant. The photoconductivity is also improved in the Cz-DNA composite, with both 4HPA-Ant and CdS multipod NCs. The enhancement in photocurrent is by more than an order of magnitude, as demonstrated by current-voltage (I-V) characterization using DNA composite photodetectors.