Robby Reynaerts

Scopus Publications

Machine learning for microscopy data analytics targeting real-time optical characterization of semiconductor nanocrystals
Amitrajit Mukherjee, Robby Reynaerts, Bapi Pradhan, Sudipta Seth, Andreas T. Rösch, Tamali Banerjee, Lata Chouhan, Handong Jin, Christian Sternemann, Michael Paulus, Luca Leoncino, Kunal S. Mali, Steven De Feyter, Maarten B. J. Roeffaers, E. W. Meijer, Johan Hofkens, Elke Debroye
Nature Communications, 2026
Semiconductor nanocrystals with uniform morphology and composition are expected to show consistent responses during light-matter interactions. However, microscopy reveals significant variations in their photoluminescence blinking patterns, even under identical experimental conditions. This discrepancy arises from differences in crystal defects and nonradiative trap states. As a result, heterogeneous blinking patterns serve as valuable indicator of material quality, uncovering several concealed features through statistical analysis of large datasets. Nonetheless, efficient segregation and analysis of numerous blinking trajectories remain a challenge due to laborious calculations, computational bottlenecks, and manual intervention. In this study, we introduce a robust unsupervised machine learning (UML) assisted module to cluster high-dimensional blinking patterns in near-real-time, while calculating category-wise power spectral densities (PSD) to investigate active traps. Furthermore, we explore the impact of data preprocessing on clustering performance. The ‘clustering-segregation-analysis’ (UML-PSD) methodology demonstrates versatility, paving a way to advance contemporary (micro)spectroscopy, specifically for rapid and cost-effective optical characterization of semiconductor nanocrystals.
Highly Ordered Co-Assembly of Bisurea Functionalized Molecular Switches at the Solid-Liquid Interface
Cosima Stähler, Robby Reynaerts, Tamara Rinkovec, Lander Verstraete, G. Henrieke Heideman, Andrea Minoia, Jeremy N. Harvey, Kunal S. Mali, Steven De Feyter, Ben L. Feringa
Chemistry A European Journal, 2024
Immobilization of stimulus‐responsive systems on solid surfaces is beneficial for controlled signal transmission and adaptive behavior while allowing the characterization of the functional interface with high sensitivity and high spatial resolution. Positioning of the stimuli‐responsive units with nanometer‐scale precision across the adaptive surface remains one of the bottlenecks in the extraction of cooperative function. Nanoscale organization, cooperativity, and amplification remain key challenges in bridging the molecular and the macroscopic worlds. Here we report on the design, synthesis, and scanning tunneling microscopy (STM) characterization of overcrowded alkene photoswitches merged in self‐assembled networks physisorbed at the solid‐liquid interface. A detailed anchoring strategy that ensures appropriate orientation of the switches with respect to the solid surface through the use of bis‐urea groups is presented. We implement a co‐assembly strategy that enables the merging of the photoswitches within physisorbed monolayers of structurally similar ‘spacer’ molecules. The self‐assembly of the individual components and the co‐assemblies was examined in detail using (sub)molecular resolution STM which confirms the robust immobilization and controlled orientation of the photoswitches within the spacer monolayers. The experimental STM data is supported by detailed molecular mechanics (MM) simulations. Different designs of the switches and the spacers were investigated which allowed us to formulate guidelines that enable the precise organization of the photoswitches in crystalline physisorbed self‐assembled molecular networks.
Self-Assembly of Discrete Oligomers of Naphthalenediimides in Bulk and on Surfaces
Christiaan H. W. A. Corbet, Bart W. L. van den Bersselaar, Bas F. M. de Waal, Robby Reynaerts, Kunal S. Mali, Steven De Feyter, Alain M. Jonas, E. W. Meijer, Ghislaine Vantomme
Chemistry A European Journal, 2024
Here, we report on the synthesis of discrete oligomers of alkyl‐bridged naphthalenediimides (NDIs) and study their molecular nanostructures both in bulk, in solution, and at the liquid‐solid interface. Via an iterative synthesis method, multiple NDI cores were bridged with short and saturated alkyl‐diamines (C3 and C12) or long and unsaturated alkyl‐diamines (u2C33 to u8C100) at their imide termini. The strong intermolecular interaction between the NDI cores was observed by probing their photophysical properties in solution. In bulk, the discrete NDI oligomers preferentially ordered in lamellar morphologies, irrespective of whether a saturated or unsaturated spacer was employed. Moreover, both the molecular architecture as well as the crystallization conditions play a significant role in the nanoscale ordering. The long unsaturated alkyl chains lead preferably to folded‐chain conformations while their saturated analogues form stretched arrangements. At the solution‐solid interface, well‐defined lamellar regions were observed. These results show that precision in chemical structure alone is not sufficient to reach well‐defined structures of discrete oligomers, but that it must be combined with precision in processing conditions.
Double Lamellar Morphologies and Odd-Even Effects in Two- And Three-DimensionalN,N′-bis(n-alkyl)-naphthalenediimide Materials
Andreas T. Rösch, Robby Reynaerts, Brigitte A.G. Lamers, Kunal S. Mali, Steven De Feyter, Anja R. A. Palmans, E.W. Meijer
Chemistry of Materials, 2021
The fabrication of highly ordered nanostructured surfaces is desirable in supramolecular chemistry and envisaged to bolster advances in heterogeneous catalysis and microelectronic applications. Here, we report on a novel set of alkylated doubleN,N′-bis(n-alkyl)-naphthalenediimides (NDIs) for the functionalization of highly oriented pyrolytic graphite (HOPG) with precise double lamellar morphologies. A detailed analysis of the two-dimensional (2D) self-assembled monolayers by scanning tunneling microscopy (STM) reveals that the structural repeating unit of the double lamellae is tuned precisely by the length of the alkyl chain that is connecting the NDI units. However, the expected odd-even effect is disturbed within the monolayers of a series of homologues. In contrast, a clear odd-even effect is observed for the melting temperatures of the respective bulk materials. Small-angle X-ray scattering reveals that these bulk materials exhibit nanophase-separated lamellar phases with domain spacings that are slightly larger than the repeating units of the double lamellar structures formed on the HOPG surface. The discrepancy is assigned to a partial desorption of the alkyl spacer from the HOPG surface, which becomes more pronounced when increasing its length. Our findings suggest that this lengthening increases the conformational freedom of the molecules on the surface while retaining a double lamellar morphology.
Coplanar versus Noncoplanar Carboxyl Groups: The Influence of Sterically Enforced Noncoplanarity on the 2D Mixing Behavior of Benzene Tricarboxylic Acids
Robby Reynaerts, Andrea Minoia, Sai Manoj Gali, Lakshya Daukiya, Niels Van Velthoven, Dirk De Vos, Roberto Lazzaroni, Kunal S. Mali, Steven De Feyter
Journal of Physical Chemistry C, 2020
Hydrogen bonding is an indispensable tenet in the fabrication of surface-confined physisorbed supramolecular networks. On-surface supramolecular chemistry is dominated by aromatic carboxylic acids, which allow implementation of highly directional and robust design elements in the form of hydrogen bonds. In this article, we investigate the influence of sterically enforced noncoplanarity of the carboxyl groups on the hydrogen-bonding ability and the self-assembly behavior of iodinated benzene tricarboxylic acid at the solution/graphite interface. The carboxylic groups of this acid are noncoplanar with respect to the benzene ring because of the bulky iodine atoms substituted on the ring. The self-assembled networks formed at the solution–solid interface were characterized at submolecular resolution using scanning tunneling microscopy (STM). The assembly behavior was scrutinized further by employing detailed molecular modeling simulations that provide an insight into the energetics of the self-assembled network formation. The on-surface mixing behavior of the iodinated, and the noniodinated analogue, the widely studied trimesic acid, was investigated. STM reveals that deposition of the two compounds on the graphite surface leads to phase separation orthogonal to the substrate and yields a supramolecular heterostructure with a well-defined bilayer. The present results indicate that, while the noncoplanarity induced by steric factor is not detrimental to the assembly behavior, it certainly contributes to the peculiar mixing behavior observed at the solution–graphite interface.
Growth of a self-assembled monolayer decoupled from the substrate: nucleation on-command using buffer layers
Robby Reynaerts, Kunal S Mali, Steven De Feyter
Beilstein Journal of Nanotechnology, 2020
Structural polymorphism is ubiquitous in physisorbed self-assembled monolayers formed at the solution–solid interface. One of the ways to influence network formation at this interface is to physically decouple the self-assembled monolayer from the underlying substrate thereby removing the influence of the substrate lattice, if any. Here we show a systematic exploration of self-assembly of a typical building block, namely 4-tetradecyloxybenzoic acid at the 1-phenyloctane–graphite interface in the presence and in the absence of a buffer layer formed by a long chain alkane, namely n-pentacontane. Using scanning tunneling microscopy (STM), three different structural polymorphs were identified for 4-tetradecyloxybenzoic acid at the 1-phenyloctane–graphite interface. Surprisingly, the same three structures were formed on top of the buffer layer, albeit at different concentrations. Systematic variation of experimental parameters did not lead to any new network in the presence of the buffer layer. We discovered that the self-assembly on top of the buffer layer allows better control over the nanoscale manipulation of the self-assembled networks. Using the influence of the STM tip, we could initiate the nucleation of small isolated domains of the benzoic acid on-command in a reproducible fashion. Such controlled nucleation experiments hold promise for studying fundamental processes inherent to the assembly process on surfaces.