3-Substituted-7-(diethylamino)coumarins as molecular scaffolds for the bottom-up self-assembly of solids with extensive π-stacking

Heterocycles as supramolecular handles for crystal engineering: a case study with 7-(diethylamino)coumarin derivatives

In this study, we present the synthesis and detailed solid-state structural characterization of a Schiff-base-bridged derivative of 7-(diethylamino)coumarin (7-DAC), a molecular block displaying repetitive aggregation modes in the solid state despite being attached to broadly different molecular frameworks. To map the supramolecular habits of this unconventional moiety, we carry out a comparative analysis of the crystal packing in a curated dataset of 50 molecules decorated with the 7-DAC group, retrieved from the literature. We uncover that self-recognition of the 7-DAC moiety has two main components: a set of directional C-H⋯O interactions between neighboring coumarins, and antiparallel dipole-dipole interactions, taking the form of distinct π-stacking modes. The pendant 7-diethylamino group is key to the behavior of 7-DAC, favoring its solubilization through its conformational flexibility in solution, while in the crystalline matrix, it acts as a structural spacer that favors π-stacking interactions. Our findings present a comprehensive analysis of the preferential arrangements of the 7-DAC fragment in various (supra)molecular scenarios, confirming that it is (i) a mobile but mostly planar group, (ii) a group prone to antiparallel aggregation, and (iii) up to 90% likely to pack via π-stacking supported by hydrogen-bonding interactions. These findings enrich the palette of supramolecular motifs available for the bottom-up design of organic materials and their programmed construction.

Exploring the self-assembly dynamics of novel steroid-coumarin conjugates: a comprehensive spectroscopic and solid-state investigation

The design, synthesis, and characterization of seven novel steroid-coumarin conjugates with diverse steroidal nuclei as lipophilic fluorescent materials for bioimaging applications are presented. The conjugates were synthesized through amidation, characterized using spectroscopic and spectrometric methods, and their main photophysical properties were determined. Dioxane : water titration experiments revealed their ability to self-assemble, forming J-aggregates as evidenced by new spectral bands at higher wavelengths. Monocrystal X-ray diffraction analysis disclosed distinctive aggregation patterns exhibiting J- or H-aggregates for selected compounds. Bioimaging studies demonstrated cell membrane localization for most conjugates, with some of them displaying an interesting selectivity for lipid droplets. Notably, the presence of the steroid fragments significantly influenced both the self-assembly patterns and the cellular localization of the fluorescent probes.

Highly crystalline and fluorescent BODIPY-labelled phenyl-triazole-coumarins as n-type semiconducting materials for OFET devices

In this work, the synthesis of BODIPY-phenyl-triazole labelled coumarins (BPhTCs) using a two-step approach is described. The influence of the BODIPY appending on the photophysical, electrochemical and thermal properties of the phenyl-triazole-coumarin precursors (PhTCs) was investigated. Band gap energies were measured by absorption spectroscopy (2.20 ± 0.02 eV in the solid and 2.35 ± 0.01 eV in solution) and cyclic voltammetry (2.10 ± 0.05 eV). The results are supported by DFT calculations confirming the presence of lowest LUMO levels that facilitate the electron injection and stabilize the electron transport. Their charge-transport parameters were measured in Organic Field-Effect Transistor (OFET) devices. BPhTCs showed an ambipolar transistor behavior with good n-type charge mobilities (10-2 cm2V-1s-1) allowing these derivatives to be employed as promising semiconducting crystalline and fluorescent materials with good thermal and air stability up to 250 °C.

3-(4-Formylphenyl)-triazole functionalized coumarins as violet-blue luminophores and n-type semiconductors: synthesis, photophysical, electrochemical and thermal properties

3-(4-Formylphenyl)-triazole-coumarin hybrid chromophores (FPhTCs) were synthesized in good yields, using a click chemistry protocol, and were also structurally characterized. Their photophysical, electrochemical and thermal properties were measured demonstrating that FPhTCs are luminescent in the blue-violet region of the electromagnetic spectrum, both in solution and the solid state. They showed an electrochemical band-gap values of 2.79 ± 0.08 eV, resistivity values between 10⁴ and 10⁵ Ω cm and are thermally stable up to 225 °C, properties that promise FPhTCs as good candidates for optoelectronic or imaging applications. Their solution and solid state photoluminescent properties are discussed and supported by theoretical calculations.

Synthesis, Optical Characterization in Solution and Solid-State, and DFT Calculations of 3-Acetyl and 3-(1'-(2'-Phenylhydrazono)ethyl)-coumarin-(7)-substituted Derivatives

Intramolecular charge transfer (ICT) effects are responsible for the photoluminescent properties of coumarins. Hence, optical properties with different applications can be obtained by ICT modulation. Herein, four 3-acetyl-2H-chromen-2-ones (1a–d) and their corresponding fluorescent hybrids 3- (phenylhydrazone)-chromen-2-ones (2a–d) were synthesized in 74–65% yields. The UV-Vis data were in the 295–428 nm range. The emission depends on the substituent in position C-7 bearing electron-donating groups. Compounds 1b–d showed good optical properties due to the D-π-A structural arrangement. In compounds 2a–d, there is a quenching effect of fluorescence in solution. However, in the solid, an increase is shown due to an aggregation-induced emission (AIE) effect given by the rotational restraints and stacking in the crystal. Computational calculations of the HOMO-LUMO orbitals indicate high absorbance and emission values of the molecules, and gap values represent the bathochromic effect and the electronic efficiency of the compounds. Compounds 1a–d and 2a–d are good candidates for optical applications, such as OLEDs, organic solar cells, or fluorescence markers.

Effect of the π-bridge on the light absorption and emission in push-pull coumarins and on their supramolecular organization

A family of eight π-extended push-pull coumarins with cross-conjugated (amide) and directly conjugated (p-phenylene, alkyne, alkene) bridges were synthesized through a convergent strategy. Using an experimentally calibrated computational protocol, their UV-Visible light absorption and emission spectra in solution were investigated. Remarkably, amide-, alkyne- and alkene-bridges undergo comparable vertical excitations. The different nature of these bridges manifests during excited-state relaxation and fluorescence. We predict that these molecules can serve as building blocks for p-type semiconductors with low reorganization energies, below 0.2 eV. Since solid-state self-assembly is crucial for this application, we examined the effect of the π-bridge over the supramolecular organization in this family of compounds to determine if stacking prevails in these π-extended coumarin derivatives. Amide and alkyne spacers allow coplanar conformations which crystallize readily; p-phenylene hinders planarity yet allows facile crystallization; alkene-bridged molecules eluded all crystallization attempts. All the crystals obtained feature dense face-to-face π-stacking with 3.5-3.7 Å interlayer distances, expected to facilitate charge transfer processes in the solid state.

R. S, Patil SA, Małecki JG, Budagumpi S. Coumarin-substituted 1,2,4-triazole-derived silver(i) and gold(i) complexes: synthesis, characterization and anticancer studies

A series of coumarin-substituted 1,2,4-triazolium salts and their respective silver– and gold– N-heterocyclic carbene complexes have been reported. The complexes displayed promising anticancer activity with GI₅₀ values of up to 0.354 μM and 8.5983 μM against MCF 7 and HT-29 cell lines, respectively.

Novel CoIII complexes containing fluorescent coumarin-N-acylhydrazone hybrid ligands: Synthesis, crystal structures, solution studies and DFT calculations

A series of new Co^III complexes of the type [Co(dien)(L1-L3)]ClO₄ (1-3), containing fluorescent coumarin-N-acylhydrazonate hybrid ligands, (E)-N'-(1-(7-oxido-2-oxo-2H-chromen-3-yl)ethylidene)-4-R-benzohydrazonate [where R=H (L1^2-), OCH₃ (L2^2-) or Cl (L3^2-)], were obtained and isolated in the low spin Co^III configuration. Single-crystal X-ray diffraction showed that the coumarin-N-acylhydrazones act as tridentate ligands in their deprotonated form (L^2-). The cation (+1) complexes contain a diethylenetriamine (dien) as auxiliary ligand and their structures were calculated by DFT studies which were also performed for the Co^II (S=1/2 and S=3/2) configurations. The LS Co^II (S=1/2) concentrated the spin density on the O-Co-O axis while the HS Co^II (S=3/2) exhibited a broad spin density distribution around the metallic center. Cyclic voltammetry studies showed that structural modifications made in the L^2- ligands caused a slight influence on the electronic density of the metal center, and the E_1/2 values for the Co^III/Co^II redox couple increased following the electronic effect of the R-substituent, in the order: 2 (R=OCH₃)<1 (R=H)<3 (R=Cl). The theoretical redox potentials (E°) of the process Co^III→Co^II were calculated for both Co^II spin states (S=1/2 and S=3/2) and a better correlation was found for Co^III→Co^II (S=1/2), compared with experimental values vs SHE (E^°_calc=-0.37, -0.36 and -0.32V vs E^°_exp.=-0.371, -0.406 and -0.358V, for 1-3 respectively). Complexes 1-3 exhibited a very intense absorption band around 470nm, assigned by DFT calculations as π-π* transitions from the delocalized coumarin-N-acylhydrazone system. 1-3 were very stable in MeOH for several days. Likewise, 1-3 were stable in phosphate buffer containing sodium ascorbate after 15h, which was attributed to the high chelate effect and σ-donor ability of the L^2- and dien ligands.