Femto- to Millisecond Time-Resolved Photodynamics of a Double-Functionalized Push–Pull Organic Linker: Potential Candidate for Optoelectronically Active MOFs

The design of improved organic linkers for the further engineering of smarter metal–organic framework (MOF) materials has become a paramount task for a wide number of material scientists. In this report, a luminescent double-functionalized push–pull (electron donor–acceptor) archetype organic molecule, dimethyl 4-amino-8-cyanonaphthalene-2,6-dicarboxylate (Me2CANADC), has been synthesized and characterized. The optical steady-state properties of Me2CANADC are strongly influenced by the surrounding environment as a direct consequence of its strong charge transfer (CT) character. The relaxation from its first electronically excited singlet state follows a double pathway: (1) on one side deactivating from its local excited (LE) state in the sub-picosecond or picosecond time domain, and (2) on the other side undergoing an ultrafast intramolecular charge transfer (ICT) reaction that is slowing down in viscous solvents. The deactivation to the ground state of these species with CT character is the origin of the Me2CANADC luminescence, and they present solvent-dependent lifetime values ranging from 8 to 18 ns. The slow photodynamics of Me2CANADC unveils the coexistence of a non-emissive triplet excited state and the formation of a long-lived charge separated state (2 µs). These observations highlight the promising optical properties of Me2CANADC linker, opening a window for the design of new functional MOFs with huge potential to be applied in the fields of luminescent sensing and optoelectronics.

KLa Determination Using the Effectiveness-NTU Method: Application to Countercurrent Absorbers in Operation Using Viscous Solvents for VOCs Mass Transfer

In this study, the Effectiveness-NTU method, which is usually applied to heat exchanger design, was adapted to gas–liquid countercurrent absorbers to determine the overall mass transfer coefficient, KLa, of the apparatus in operation. It was demonstrated that the ε-NTU method could be used to determine the KLa using the Henry coefficient of the solute to be transferred (HVOC), the gas flow-rate (QG), the liquid flow-rate (QL), the scrubber volume (V), and the effectiveness of the absorber (ε). These measures are calculated from the gaseous concentrations of the solute measured at the absorber inlet (CGin) and outlet (CGout), respectively. The ε-NTU method was validated from literature dedicated to the absorption of volatile organic compounds (VOCs) by heavy solvents. Therefore, this method could be a simple, robust, and reliable tool for the KLa determination of gas–liquid contactors in operation, despite the type of liquid used, i.e., water or viscous solvents.

Direct observation of impact propagation and absorption in dense colloidal monolayers

Dense colloidal suspensions can propagate and absorb large mechanical stresses, including impacts and shocks. The wave transport stems from the delicate interplay between the spatial arrangement of the structural units and solvent-mediated effects. For dynamic microscopic systems, elastic deformations of the colloids are usually disregarded due to the damping imposed by the surrounding fluid. Here, we study the propagation of localized mechanical pulses in aqueous monolayers of micron-sized particles of controlled microstructure. We generate extreme localized deformation rates by exciting a target particle via pulsed-laser ablation. In crystalline monolayers, stress propagation fronts take place, where fast-moving particles (Vapproximately a few meters per second) are aligned along the symmetry axes of the lattice. Conversely, more viscous solvents and disordered structures lead to faster and isotropic energy absorption. Our results demonstrate the accessibility of a regime where elastic collisions also become relevant for suspensions of microscopic particles, behaving as “billiard balls” in a liquid, in analogy with regular packings of macroscopic spheres. We furthermore quantify the scattering of an impact as a function of the local structural disorder.

Ultrafast dynamics and solvent-dependent deactivation kinetics of BODIPY molecular rotors

The fluorescent excited state of a molecular rotor based on the meso-substituted boron-dipyrromethane (BODIPY) core decays rapidly to the ground state via a conical intersection. The fluorescence is strongly increased in viscous solvents, but solvent polarity has only a small effect.