Flip de Jong

Substitution of the iminothioindoxyl core with heteroaryl residues yields HA-ITI photoswitches that exhibit fast T-type behavior, red-shifted visible absorption, and large E / Z band separation.

Combining nonlinear optical processes and photoswitching transcends the limitations of conventional and even standalone super-resolution imaging. While photoswitching enables resolution improvement, it is typically constrained by limited imaging depth, potential phototoxicity and the low number of inherently fluorescent photoswitches. Nonlinear excitation, such as two-photon absorption, addresses some of these challenges. Here, we present a molecular design strategy that unites the molecular control of T-type negative photoswitches (PS) and two-photon absorption. In these designs, two-photon absorbing push-pull fluorophores that function as FRET-donors are linked to T-type negative PS FRET-acceptors, e.g., donor-acceptor Stenhouse adducts (DASA) or 1,1′-binaphthyl-bridged imidazole dimers. FRET-sensitized isomerization of PS is delicately balanced by reverse thermal isomerization and results in nonlinearly potentiated fluorescence with a quartic fluorescence response upon two-photon excitation, implying enhanced spatial resolution potential. The use of T-type PS is instrumental to this approach, as it ensures temporally stable photonic responses and recyclability without incurring irreversible saturation effects.

Nucleation, the pivotal first step of crystallization, governs the essential characteristics of crystallization products, including size distribution, morphology, and polymorphism. While understanding this process is paramount to the design of chemical, pharmaceutical, and industrial production processes, major knowledge gaps remain, especially with respect to the crystallization of porous solids. Also for nanocrystalline ZIF-8, one of the most widely studied metal-organic frameworks, questions regarding the species involved in the nucleation pathway and their structural and chemical transformations remain unanswered. By combining harmonic light scattering, inherently sensitive to structural changes, with NMR spectroscopy, which reveals molecular exchanges between particles and solution, we were able to capture the crystallization mechanism of ZIF-8 in unprecedented detail. This dual approach provides concurrent structural and chemical insights, revealing key processes not previously observed in ZIF crystallization. Upon mixing, small charged prenucleation clusters (PNCs) are formed, exhibiting an excess of ligands and net positive charge. We show that nucleation is initiated by aggregation of PNCs, through the release of ligands and associated protons to the liquid. This leads to the formation of charge neutral amorphous precursor particles (APPs), which incorporate neutral monomers from the solution and crystallized ZIF-8. Our work highlights chemical dynamics as a vital, yet often overlooked, dimension in the multistage structural evolution of MOFs. By establishing the critical role of PNCs in the nucleation of ZIF-8, new pathways open up for controlling crystallization of metal-organic frameworks through targeted chemical interactions with these species.

Metal-organic frameworks are crystalline materials that do not always have a perfect stoichiometry, due to the presence of defects, modulators or mixed linkers. A common approach to quantify these defects is to define a value for ‘missing linkers’, typically done by thermogravimetric analysis (TGA). We propose the use of the (metal oxide) residue of TGA to quantify the metal content in combination with quantitative NMR spectroscopy of a digested sample for linker quantification. We demonstrate this simple concept for three examples, MAF-6, ZIF-8 and MOF-5.

Methyl 4-(1,3a,6a-triazapentalen-3-yl)benzoate (TAP1) shows interesting properties as a small molecule fluorophore. In the search for post-functionalization methods, palladium-catalyzed arylation reactions were demonstrated. Direct CH arylation reactions of TAP1 with various aryl halides resulted in 3,6-diaryltriazapentalenes TAP4, although mostly in poor yields. Bromination of TAP1 followed by Suzuki coupling, on the other hand, requires a more delicate procedure, but gave arylated products with the same regiochemistry (TAP4) in moderate to good yields. The structure of 6-phenyltriazapentalene TAP4a was confirmed by crystallographic analysis. In addition, the effect of the C6 arylation on the fluorescent properties of 3-aryl-1,3a,6a-triazapentalenes was studied in dichloromethane at room temperature and in 2-methyltetrahydrofuran at 77 K, while the photophysical properties of two saponified derivatives were measured in acetonitrile.

A new family of unsymmetrical boron chromophores chelated with two BF₂ units, named BOPAM, has been developed via a one‐pot, three‐step reaction starting from commercially available thioamides via i) conversion to amidrazones, ii) condensation with pyrrole aldehydes, and iii) boron chelation. This synthetic pathway has been proven to be highly efficient, having a broad substrate tolerance and giving the BOPAM products high yield. Notably, some of the BOPAM dyes show interesting photophysical properties with fluorescence quantum yields up to 0.98 in toluene. A fine‐tuning of their emissive properties has been attained through tailored molecular design strategies guided by in‐depth computational investigations. Tailored substitution with electron‐donating groups at the BOPAM ring leads to the opening of a non‐radiative decay channel involving a dark state and consequently a significant quenching of the fluorescence. The study is complemented by exhaustive steady‐state and time‐resolved spectroscopic measurements.

Electrostatic interactions between the zeolite cavityand confinednoble-metal nanoparticles govern the photophysical properties of thesematerials. A better understanding of these interactions can affordnew perspectives in optoelectronics applications. We investigatedthis interplay by revealing the peculiar photophysical propertiesof Ag clusters embedded in nanosized faujasite zeolite structures.Crystal size and steady state optical properties were characterizedvia integrated light and electron microscopy (ILEM) and steady statespectroscopy. Extensive time-resolved spectroscopy experiments performedon femtosecond to millisecond time scales revealed excited state dynamicsthat are intriguingly different from those observed for their micrometersized counterpart. Multiscale modeling investigations were performedto rationalize the effect of the crystal size on the photophysicalproperties. Our results indicate that for the nanosized crystals,the emissive properties as well as the radiative and nonradiativeprocesses involving the Ag clusters are dramatically dependent onthe surface charge density and surface charge balance.

MACl post-treatment of MAPbI₃ nanoparticles in a mixed solvent successfully suppresses surface traps, associated with an improved PL intensity and lifetime, brighter and longer ON-states in PL blinking, and a more stable, enhanced photocurrent.