Stijn Van Cleuvenbergen

KU Leuven | ku leuven · Molecular electronics and Photonics, Chemistry Dpt.

Organic materials are promising candidates for integration in optical network components allowing fast communication. Ultimate speeds can be obtained by exploiting third-order nonlinear optical light-matter interactions that ultimately rely on the molecular second hyperpolarizability (γ). The exploration of molecular structure-property relations is...

Metal–organic framework ZIF-8, from the zeolitic imidazolate framework family, shows a large intrinsic second-order nonlinear optical (NLO) response. In addition, ZIF-8 is a stable, inexpensive material that is transparent in the visible (vis) and near-infrared (NIR) window. This is crucial for NLO applications. The second-order NLO activity is due...

Interpenetration, the entwining of multiple lattices, is a common phenomenon in metal-organic frameworks (MOFs). Typically, in interpenetrated MOFs the sub-lattices are fully occupied. Here we report a family of MOFs in which one sub-lattice is fully occupied and the occupancy level of the other can be controlled during synthesis to produce framewo...

Optical interrogation of cellular electrical activity has proven itself essential for understanding cellular function and communication in complex networks. Voltage‐sensitive dyes are important tools for assessing excitability but these highly lipophilic sensors may affect cellular function. Label‐free techniques offer a major advantage as they eli...

Optical interrogation of cellular electrical activity has proven itself essential for understanding cellular function and communication in complex networks. Voltage-sensitive dyes are important tools for assessing excitability but these highly lipophilic sensors may affect cellular function. Label-free techniques offer a major advantage as they eli...

Nonlinear optical (NLO) properties of three chiral smectic liquid crystals were investigated by Hyper-Rayleigh Scattering (HRS) and the Second-Harmonic Generation (SHG) methods. The HRS measurements of two compounds (MHPOBC and D16), with the biphenyl unit in their center, in solution demonstrate the quadratic NLO activity. The third compound (D17)...

In situexperimental studies have been key in uncovering the often elusive pathways of nucleation and crystal growth. In the field of material science and medicine this offers the prospect of controlling crystallization processes to fight disease or tailor materials towards specific applications. To further advance this quest there is a need for fle...

The preparation of gold nanoparticles through reduction of chloroauric acid by trisodium citrate, also known as the Turkevich synthesis, was analysed both ex situ and in situ. In situ experiments consist of dynamically tracking second and third harmonic light scattering and multiphoton luminescence. By complementing in situ data with ex situ quench...

Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular aggregates upon lowering the solvent quality. This supramolecular organization largely determines the optical and electronic properties of these polymers. However, despite numerous studies the exact mechanism and kinetics of the aggregation process and t...

The wings of some insect species are known to fluoresce under illumination by ultraviolet light. Their fluorescence properties are however, not comprehensively documented. In this article, the optical properties of one specific insect, the Trichtenotoma childreni yellow longhorn beetle, were investigated using both linear and non‐linear optical (NL...

Di‐ and tetra‐Ruthenium alkynyl complexes with Y‐ and distorted H‐shaped geometries, respectively, possess significant quadratic (former), cubic and quintic (latter) nonlinear optical properties. The cover image emphasizes that their structures are reminiscent of aspects of Australia's iconic Parliament House which is built into a hill in Canberra...

Syntheses of bis[bis{1,2‐bis(diphenylphosphino)ethane}ruthenium]‐functionalized 1,3,5‐triethynylbenzene‐cored complexes via "steric control" permit facile formation of Y‐shaped Sonogashira coupling products and distorted‐H‐shaped homo‐coupled quadrupolar products. The wavelengths of the linear optical absorption maxima are dominated by the nature o...

Recent developments in nonlinear optical light scattering techniques have opened a window into morphological and structural characteristics for a variety of supramolecular systems. However, for the study of dynamic processes, the current way of measuring is often too slow. Here we present an alternative measurement scheme suitable for following dyn...

The colors of photonic crystals are based on their periodic crystalline structure. They show clear advantages over conventional chromophores for many applications, mainly due to their anti‐photobleaching and responsiveness to stimuli. More specifically, combining colloidal photonic crystals and invisible patterns is important in steganography and w...

The novel 2D bismuth‐camphorate IEF‐1, formulated as [Bi(L)(HL)] (where H2L = camphoric acid), has been successfully isolated as large single‐crystals and easily scaled‐up by hydrothermal synthesis. The crystalline structure of IEF‐1 was unveiled by single‐crystal X‐ray diffraction, crystallizing in the monoclinic space group P21, and fully charact...

Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as non-linear o...

The design of efficient noncentrosymmetric materials remains the ultimate goal in the field of organic second-order nonlinear optics. Unlike inorganic crystals currently used in second-order nonlinear optical applications, organic materials are an attractive alternative owing to their fast electro-optical response and processability, but their alig...

The design of efficient noncentrosymmetric materials remains the ultimate goal in the field of organic second-order nonlinear optics. Unlike inorganic crystals currently used in second-order nonlinear optical applications, organic materials are an attractive alternative owing to their fast electro-optical response and processability, but their alig...

Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confi...

The molecular first hyperpolarizability (β) of bacteriorhodopsin is measured over a broad spectral range (800-1300 nm) by means of a spectral hyper-Rayleigh scattering setup. We observe that two photon fluorescence introduces a systematic error towards overestimating the β value. Spectrally resolved hyper-Rayleigh scattering allowed us to quantify...

H. coerulea’s elytra show a strong two-photon fluorescence signal, which depends on the presence of water in the photonic structure. A polarization-dependent Third Harmonic Generation signal was detected as well and thoroughly investigated.

Up to now colloidal photonic crystal (CPC) lasers essentially relied on photonic band gap edge effects, as a consequence of the poor passband quality achieved by previously reported engineering methods. In this paper, we demonstrate lasing oscillation in CPCs based on the defect mode passband effect. As defect mode, we introduce a high quality mono...

Direct reactive ion etching (RIE) of hollow SiO2 sphere colloidal crystals (HSCCs) is employed as a facile, low-cost method to fabricate complex three-dimensional (3D) hierarchical nanostructures. These multilayered structures are gradually transformed into nanostructures of increasing complexity by controlling the etching time, without complicated...

Inspired by the limpet's shell, this study reports an inexpensive and straightforward strategy to create sealed photonic crystals from colloidal hollow microspheres. From the mechanically sealed structure and the periodically isolated air microcavities, the resulting sealed colloidal crystals show enhanced mechanical robustness and an ultrastable p...

The first hyperpolarizabilities of [Au25(SR)18]-1/0 and Au38(SR)24 clusters were determined by Hyper-Rayleigh Scattering. A strong dependence on the molecular symmetry was observed, and we explore two strategies to destroy the center of inversion in [Au25(SR)18]-1/0, protection by chiral ligands and alloying of the cluster with silver. This may ope...

Polar Metal-Organic Frameworks have potential applications as functional non-linear optical, piezoelectric, pyroelectric and ferroelectric materials. Using second harmonic generation microscopy we found that fluoride doping of the microporous iron(III) terephthalate MOF MIL-53(Fe) induces a polar organization in its structure, which was not previou...

An optomicrofluidic device was developed by introducing 3D wettability patterns into hollow SiO2 sphere colloidal photonic crystals. Aqueous liquids flow through the superhydrophilic channel due to the surface tension confinement effect. Based on the significant fluorescence enhancement from photonic band gap (PBG) effects in these channels, real-t...

Thiolate-protected gold clusters are promising candidates for imaging applications due to their interesting, size-dependent properties. Their high stability and the ability to functionalize the clusters with biocompatible ligands render the clusters for various imaging techniques such as fluorescence microscopy or Second-Harmonic Generation microsc...

A series of new bipyrimidine-based chromophores have been prepared presenting alkoxystyryl donor groups carrying aliphatic chains in the 3,4, 3,5 or 3,4,5 positions, connected to electron-accepting 2,2′-bipyrimidine cores. Their linear and nonlinear optical properties were investigated as well as their mesomorphic properties by various techniques (...

Disubstituted poly(phenanthrene), a conjugated polymer, has been studied by hyper-Rayleigh scattering. Although this compound lacks the donor–acceptor motif that is typically associated with a strong second-order nonlinear optical response, the (intrinsic) hyperpolarizability ranks among the highest ever measured, breaking the longstanding apparent...

Three-dimensionally (3D) ordered macroporous materials combine interesting structural and optical properties. Accessible and economic fabrication is essential to fully explore the unique possibilities these materials present. A common method to fabricate 3D ordered macroporous materials is by self-assembling colloids, resulting in so-called opals....

Three-dimensionally ordered macroporous materials have unique structural and optical properties, making them useful for numerous applications in catalysis, membrane science and optics. Accessible and economic fabrication of these materials is essential to fully explore the many possibilities that these materials present. A new templating method to...

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these propertie...

Four new HAT derivatives with octupolar symmetry have been synthesized. Their linear and nonlinear optical, photophysical, and electrochemical properties have been rationalized in terms of donor–acceptor interactions. We get further insights in the relationship between experimental first hyperpolarizability and two-photon absorption cross section:...

A set of chiral discotic phenylacetylenes has been synthesized by threefold Sonogashira-coupling between different ethynylbenzenes and triiodobenzenes. The resultant bulk materials are fully characterized by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction. The octopolar nature of the target compoun...

Previous studies on the radiation effects upon polymer and polymer-based photonic materials suggest that the radiation resistance of the material is heavily dependent on the choice of polymer-host and guest-chromophore. To date, the best results have been achieved with electro optic polymeric materials based on CLD1 doped in APC, which has resulted...

A comprehensive series of systematically functionalized C3-symmetric hexakis (para-substituted) triindoles has been studied for its linear and second-order nonlinear optical properties. The carbazole-derived triindole central core is electron rich and electron donating. The peripheric substitution pattern, resulting in a donor–donor or a donor–acce...

Organic microcrystals obtained from an octupolar molecule are studied by polarized nonlinear optical microscopy. While two-photon fluorescence microscopy is employed to verify the monocrystallinity of the analyzed domains, second-harmonic generation microscopy allowed determination of the point group symmetry of the crystallites. This combined anal...

A combined UV-visible, cyclic voltammetric theoretical and hyper-Rayleigh scattering study has been carried out on a new series of ferrocenyl chromophores (2a–2d and 7–11) to develop a structure–property relationship, by varying the acceptor strength and the conjugation path length between the donor and the acceptor and by disubstitution of the fer...

A series of chromophores with enhanced second- and third-order nonlinear optical properties were engineered for use in combined second-harmonic and two-photon fluorescence microscopy. Electron-accepting moieties imparted nonlinear optical properties to the chromophores. The electron-rich carbazole core served as a template towards one- or two-dimen...

The alkynes HC CC6H2-2,6-Et-2-4-C CC6H4-4-NO2 (4) and HC CC6H4-4-C CC6H2-2,6-Et-2-4-C CC6H4-4-NO2 (6) and gold alkynyl complexes Au{C CC6H2-2,5-(OEt)(2)-4-C CC6H4-4-NO2}(PPh3) (7), Au(C CC6H2-2,6-Et-2-4-C CC6H4-4-NO2)(PPh3) (8), and Au(C CC6H4-4-C CC6H2-2,6-Et-2-4-C CC6H4-4-NO2)(PPh3) (9) have been synthesized. The linear optical properties and qua...

Carbazole-derived chromophores with enhanced second- and third-order nonlinear optical properties were engineered and characterized for their nonlinear optical properties, for ultimate use in combined second-harmonic and two-photon fluorescence microscopy imaging. Electron accepting moieties imparted the nonlinear optical properties to the chromoph...

Four new dipolar cations have been synthesized, containing ferrocenyl electron donor groups and diquaternized 2,2′-bipyridyl (diquat) acceptors. To our knowledge, these are the first organometallic diquat derivatives to be reported and have been characterized as their PF6– salts by using various techniques including 1H NMR and electronic absorption...

In the quest for organic second-order nonlinear materials, self-assembled structures based on octupolar molecules have shown to be promising candidates. The presented work focuses on an octupolar substituted 1,3,5-trisalkynylbenzene that forms crystals that show significant second-harmonic generation (SHG). Continuous polarization SHG measurements...

The effect of extending the conjugation length, the deployment of various substituents and configurational locking of the polyene backbone on the second-order nonlinear optical (NLO) response of a series of indoline based compounds has been investigated. The compounds were examined using Hyper-Rayleigh scattering (HRS) and relative second-harmonic...

In general, second-harmonic generation (SHG) microscopy is used to image highly ordered structures in biological samples, like starch, collagen, myosin and tubulin. In an effort to expand the possible targets for SHG microscopy, a number of new fluorescent probes with high performance in SHG imaging were designed and synthesized. The design is base...

We have synthesized three new molecules that have three thienylethynyl arms substituting a central benzene core and different electron donor/acceptor groups in the three remaining phenyl positions. The absorption, fluorescence, phosphorescence, and transient triplet-triplet spectra are analyzed in the light of the electronic structure of the ground...