Uwe Pischel

University of Huelva | UHU · CIQSO - Center for Research in Sustainable Chemistry

Fluorescent molecules play a crucial role in biomedicine by facilitating the visualization and tracking of biological processes with sensitivity and specificity. However, tailoring their structure to meet the demands of live cell and in vivo imaging presents a significant challenge due to the intricate interplay of factors governing their structura...

UV-light curing polyurethane-urea adhesives (PU-urea) were formulated from 4,4′-methylenediphenyl diisocyanate (MDI), 1,5-pentanediol (PD), 1,5-pentanediamine (cadaverine, CAD), and acetone as the adhesive carrier. The UV light-triggered curing process of these PU-urea formulations was controlled by blocking hydroxyl and amine functional groups of...

A series of six azaborahelicenes with varying electron-donor substitution at the 4-position of the aryl residue (i.e., naphthyl) or with variable π-extension of the aryl residue (thianthrenyl, anthryl, pyrenyl) was prepared with an efficient and flexible synthetic protocol. These different types of functionalization afforded notably pronounced intr...

Ferroptosis is an iron-dependent lipid peroxidation-driven mechanism of cell death and a promising therapeutic target to eradicate cancer cells. In this study we discovered that boronic acid derived salicylidenehydrazone (BASHY) dyes are highly efficient singlet-oxygen photosensitizers (PSs; quantum yields up to 0.8) that induce ferroptosis trigger...

A series of dithienylethene (DTE) photoswitches with aza-heteroaromatic cationic moieties was synthesized. The switches were characterized regarding their photochemical and photophysical properties in acetonitrile and in water. The efficiency of the switching and the photostationary state composition depend on the degree of π-conjugation of the het...

A set of nine boronic‐acid‐derived salicylidenehydrazone (BASHY) complexes has been synthesized in good to very good chemical yields in a versatile three‐component reaction. In an extension to previous reports on this dye platform, the focus was put on the electronic modification of the “vertical” positions of the salicylidenehydrazone backbone. Th...

The tailored design of a light-triggered supramolecular cascade results in an artifical machinery that assimilates the transduction of photons into chemical communication and the final release of a neurotransmitter. This...

Two four‐coordinate organoboron N,C‐chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF‐7 cells. Their excited‐state properties are characterized by time‐resolved pump‐probe spectroscopy and fluorescence lifetime microscopy. The excited‐state relaxation...

A bichromophoric dyad composed of a Prodan-derived moiety and a BODIPY dye was prepared, photophysically characterized, and tested for multiphoton fluorescence microscopy of N13 microglial cells. The dyad shows highly efficient energy transfer, independent on the solvent polarity of the medium. However, in polar media photoinduced electron transfer...

Logic operations are typically performed by silicon‐based microprocessors. Over the last 30 years, research groups are aiming at teaching molecules to do so too. This research field is referred to as molecular logic, or molecular information processing. While the inputs and outputs in the traditional devices are voltage driven, the molecular versio...

Host–guest complexation of dithienylethene photoswitches with cucurbit[8]uril leads to photoresponsive binding pairs with picomolar affinity in water.

Polycyclic aromatic hydrocarbon chromophores that show an ideal bipartition between fluorescence and singlet oxygen production have been developed.

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that is characterized by the presence of demyelinated regions with accumulated myelin lipid debris. Importantly, to allow effective remyelination, such debris must be cleared by microglia. Therefore, the study of microglial activity with sensitive tools is of great int...

The selective photodeprotection of the NVoc-modified FGG tripeptide yields the transformation of its 1:1 receptor-ligand complex with cucurbit[8]uril into a homoternary FGG2@CB8 assembly. The resulting light-induced dimerization of the model peptide provides a tool for the implementation of stimuli-responsive supramolecular chemistry in biologicall...

In this Review the use of light to address stimuli-responsive molecular and supramolecular systems with applications in information processing and binary logic is discussed. Molecular photoswitches are at the focal point of the herein summarized works. Light offers great advantages in terms of spatiotemporal control and remote triggering. As an add...

Boronic acid‐derived salicylidenehydrazone complex (BASHY) dyes with a polymethine backbone were designed to yield efficient red‐emitting and two‐photon absorbing fluorophores that can be used as markers for astrocytes. The dyes are chemically stable in aqueous solution and do not undergo photodecomposition. Their photophysical properties can be el...

Boronic acid derived salicylidenehydrazone (Bashy) complexes can be designed as bright fluorescent dyes with tunable emission in the red spectral window. The image shows the structural development from parent Bashy towards cyanine‐like π‐expanded Bashy dyes that can be employed for the bioimaging of astrocytes. Astrocytes are star‐shaped cells that...

The light‐gated organocatalysis via the release of 4‐N,N‐dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]²⁺ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre‐catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455...

The combination of two two-photon-induced processes in a FRET-operated photochromic fluorene-dithienylethene dyad lays the fundament for the observation of a quartic dependence of the fluorescence signal on the excitation light intensity. While this photophysical behavior is predicted for a four-photon-absorbing dye, the herein proposed approach op...

Stimuli-responsive chemical communication is enabled in a self-sorted system of cucurbituril host–guest complexes.

Calix[4]pyrrole phosphonate-cavitands were used as receptors for the design of supramolecular sensors for creatinine and its lipophilic derivative hexylcreatinine. The sensing principle is based on indicator displacement assays of an inherently fluorescent guest dye or a black-hole quencher from the receptor’s cavity by means of competition with th...

Four new dyes that derive from borylated arylisoquinolines were prepared, containing a third aryl residue (naphthyl, 4-methoxynaphthyl, pyrenyl or anthryl) that is linked via an additional stereogenic axis. The triaryl cores were synthesized by Suzuki couplings and then transformed into boronic acid esters by employing an Ir(I)-catalyzed reaction....

Four-coordinate N,C-chelate organoboron dyes with alkynyl spacers were synthesized by Heck alkynylation. These dyes are π-extended analogues of the recently reported class of four-coordinate borylated arylisoquinolines (BAI). Depending on the electron-donor substitution they feature intramolecular charge-transfer (ICT) character in the excited stat...

Uwe Pischel is a Professor of Organic Chemistry at the University of Huelva (Spain) and Group Leader at the Center for Research in Sustainable Chemistry (CIQSO). He is a current member of the ChemPhotoChem Editorial Board.

In this chapter, the preparation of cucurbituril-based pseudorotaxanes, rotaxanes and polyrotaxanes is illustrated with selected examples. This includes the notions of self-sorting, which enables the setup of homo- and hetero(pseudo)rotaxanes. The implications of thermodynamic and kinetic control are briefly showcased as well. In the main part, the...

The formation of host-guest complexes between seven flavylium cations and water-soluble p-sulfonatocalix[4]arene (SC4) was investigated by UV/vis-absorption, fluorescence, and NMR spectroscopy. The results show that this family of cationic guests form complexes with affinities in the sub-millimolar range. A representative chalcone/flavylium photosw...

The composition of a supramolecular network, constituted by several cucurbituril receptors and guests, can be controlled by the reversible and all-photonic switching of a dithienylethene guest.

A combination of a chalcone/flavylium photoswitch with a supramolecular host–guest complex that can be used to phototrigger the logically-controlled and selective release of cargo was devised.

Racemic mixtures of boronic acid-derived salicylidenehydrazone (BASHY) complexes were enantiomerically resolved. The chiroptical properties of the stereoisomers, containing an asymmetric boron as the only stereogenic unit, are translated into mirror-imaged electronic circular dichroism spectra and circularly polarized luminescence (CPL, dissymmetry...

We report herein the controlled surface functionalization of micro- and nanoparticles by supramolecular host-guest interactions. Our idea is to exploit the competition of two high affinity guests for binding to the surface-bound supramolecular host cucurbit[7]uril (CB7). To establish our strategy, surface azide groups were introduced to hard-sphere...

Eucalyptol, fenchyl alcohol, and geranylamine were tested for the binding to cucurbit[8]uril. Nanomolar affinities were found, giving rise to a highly selective binding of the terpenes by cucurbit[8]uril when compared to the smaller cucurbit[7]uril. This was rationalized with a better size fit with the larger macrocycle. These notions were supporte...

Energy transfer cassettes that build on the platform of boronic acid derived salicylidenehydrazone (BASHY) complexes were prepared. The functional flexibility of the BASHY chromophore was underpinned by its tunable role as energy donor or acceptor, integrated in compact and non‐conjugated bichromophoric dyads. The energy transfer is highly efficien...

Three helicenes based on a borylated arylisoquinoline skeleton have been prepared in their enantiopure forms and characterized with respect to their photophysical properties, including the use of chiroptical spectroscopies. The dyes show varying charge‐transfer character and efficient emission (quantum yields between 0.13 and 0.30, in toluene), whi...

The idea of using molecules in the context of information security has sparked the interest of researchers from many scientific disciplines. This is clearly manifested in the diversity of the molecular platforms and the analytical techniques used for this purpose, some of which we highlight in this Tutorial Review. Moreover, those molecular systems...

The Cover Feature highlights the bright fluorescence emission of two of the several four-coordinate organoboron N,C-chelate dyes investigated in this work. The artwork (provided by Zoe Domínguez, University of Huelva) illustrates the different charge-transfer character exhibited by each dye and provides some key photophysical data in a simplified J...

Bis(dioxaborine) dyes of the A-π-A format (A: acceptor, π: conjugated bridge) were prepared and photophysically characterized. The best performing dyes feature (a) visible-light absorption (>400 nm), (b) high molar absorption coefficients (up to 70000 M-¹cm-¹), (c) Stokes shifts in the range of ca. 3000-5000 cm-¹, and (d) strong fluorescence emissi...

The excited-state behavior of four-coordinate N,C-chelate organoboron dyes, based on arylisoquinoline ligands with varying degree of charge-transfer character, was characterized. Data related to excited triplet state formation, oxygen quenching, and singlet-oxygen formation were obtained. The results jointly rationalize the previously observed high...

A series of boronic acid derived salicylidenehydrazone (BASHY) complexes was prepared and photophysically characterized. The dye platform can be modified by (a) electronic tuning along the cyanine-type axis via modification of the donor–acceptor pair and (b) functional tuning via the boronic acid residue. On the one hand, approach (a) allows the co...

A general approach toward the light-induced guest release from cucurbit[7]uril by means of a photoactivatable competitor was devised. An o-nitrobenzyl-caged competitor is photolyzed to generate a competitive guest that can displace cargo from the host macrocycle solely based on considerations of chemical equilibrium. With this tool the release of t...

In this Minireview conceptual approaches towards the communication between (supra)molecular species are illustrated. The reviewed mechanisms include photophysical communication through energy transfer and communication mediated by chemical species that are released from precursors upon application of an external stimulus. The focus is on the stimul...

Supplementary

Pseudorotaxanes can be obtained by self-sorting using heteroditopic guests and various cucurbituril homologues as hosts. The assembly and chemically induced disassembly of the pseudorotaxanes can be monitored by measuring the fluorescence of the anthracene guest in solution. Mass spectral evidence for the supramolecular assemblies is obtained in th...

We thank FCT Portugal (Doctoral Fellowship, SFRH/BD/94779/2013 to F. M. F. S., Postdoctoral Fellowship, SFRH/BPD/103172/2014 to P. M. S. D. C.; projects PTDC/QUI-QUI/118315/2010 and PTDC/BBB BQB/0506/2012; PTDC/QEQ-QOR/1434/2014: PTDC/SAUFAR/119389/2010; FCT Investigator to G. J. L. B. and P. M. P. G.; iMed.ULisboa grant UID/DTP/04138/2013), EU (Ma...

We report the selective formation of cyclohexenes with a tetrasubstituted double bond, the structural key element of megastigmanes. For this purpose the ZrCl4-mediated epoxide ring opening of epoxy-geranylacetone was employed. This approach provides a universal entry to the preparation of the members of the megastigmane family, which was exemplifie...

Fluorophores are indispensable for imaging biological processes. We report the design and synthesis of azide-tagged boronic acid salicylidenehydrazone (BASHY) dyes and their use for site-selective labelling of Annexin V. The Annexin V-BASHY conjugate maintained function and fluorescence as demonstrated by the targeted detection of apoptotic cells.

A new fluorescent acrylamide-type monomer bearing a hydrogen bonding- and polarity-sensitive benzocoumarin fluorophore was synthesized. The absorption spectra, fluorescence spectra, and fluorescence lifetime of a model compound were measured in ten solvents with different hydrogen-bonding abilities and polarities to investigate the sensitivity of t...

Seven tetracoordinate organoboron fluorophores with heterobiaryl N,O- or N,N-chelate ligands were prepared and photophysically characterized (in toluene). The electronic variation of the heteroaromatic moiety provided a means for the fine-tuning of the UV/vis absorption and emission spectra. In the most interesting cases, the spectra were red-shift...

Controlling a host-guest equilibrium with a flavylium-based photoswitch leads to the efficient light-triggered release of memantine, a widely prescribed Alzheimer's drug. The artwork, provided by Zoe Domínguez, highlights the displacement of the memantine drug from a cucurbituril macrocycle through the photoinduced transformation of a trans-chalcon...

The reversibly switchable trans-chalcone/flavylium photochromic system was successfully coupled to the complexation equilibrium of a drug-cucurbit[7]uril host-guest assembly. Hence, the phototriggered release of memantine under illumination at 366 nm was observed. The process can be partially reverted through a thermally activated back reaction.

A method for the phototriggered release of a biogenic amine from the host-guest complex with the cucurbit[7]uril macrocycle in aqueous solution was devised. The approach exploits a photoinduced pH jump from 8 to 5, combined with the pH-dependent switching of the competitive capacity of a guest dye. The fluorescence fingerprint of the competitor can...

The photo-controlled shift of pH titration curves, describing the acidochromic behaviour of a spiropyran switch network, was harnessed for the realisation of a molecular triode. The intricate network can be correctly interpreted with respect to the pH dependence of the main involved species.

The modular assembly of boronic acids with Schiff-base ligands enabled the construction of innovative fluorescent dyes [boronic acid salicylidenehydrazone (BASHY)] with suitable structural and photophysical properties for live cell bioimaging applications. This reaction enabled the straightforward synthesis (yields up to 99 %) of structurally diver...

The modular assembly of boronic acids with Schiff-base ligands enabled the construction of innovative fluorescent dyes [boronic acid salicylidenehydrazone (BASHY)] with suitable structural and photophysical properties for live cell bioimaging applications. This reaction enabled the straightforward synthesis (yields up to 99 %) of structurally diver...

Six strongly fluorescent four-coordinate organoboron N,C chelates containing an aryl isoquinoline skeleton were prepared. Remarkably, the fluorescence quantum yields reach values of up to 0.74 in oxygen-free toluene. The strong BN interaction was corroborated by the single-crystal X-ray analysis of two dyes. The intramolecular charge-transfer char...

Novel diastereomeric triads containing two naphthalene chromophores have been designed in which an electron-donating amine moiety is covalently integrated into the connecting bridge. Photophysical studies (steady-state and time-resolved fluorescence) in solvents of different polarity have been performed. A remarkable stereodifferentiation in the in...

Cucurbiturils (CB6 and CB7) were shown to inhibit the enzymatically catalyzed restriction of plasmids and linear DNA. This effect can be inverted by supramolecular masking of the macrocycles through competitive complexation with polyamines. These experiments provide supramolecular control of biocatalytic processes.

The reversible photoswitching between an anthracene derivative and its [4+4] dimer, using the template effect of the CB8 macrocycle, was demonstrated. This example of supramolecular chemistry in water was harnessed to demonstrate the operation of a keypad lock device that is driven by means of light and chemicals as inputs.

In this tutorial review, the most recent developments in the field of molecular logic and information processing are discussed. Special emphasis is given to the report of progress in the concatenation of molecular logic devices and switches, the design of memory systems working according to the principles of sequential logic, the mimicking of trans...

This article shows how to teach molecules the basics of logic and how to integrate complicated logic operations with relatively simple molecules. A special focus is put on the realization of multi-level fluorescent switches with chemical inputs as well as on the demonstration of various memory-based operations with all-optical photochromic switches...

One of the applications of cationic porphyrins is their use in microbial photodynamic inactivation (PDI). For this purpose there is a constant quest for new cationic photoactive derivatives. In this work, we synthesized and fully characterized a new porphyrin 3a and the corresponding cationic derivative 3b. The results presented here show that meso...

A new approach towards the rapid identification of quality binders to cucurbiturils—those that combine high affinity with high selectivity for a particular homologue—was developed. The assay exploits macrocycle-specific optical fingerprints (colorimetric or fluorimetric) of carefully selected indicators dyes. The screening of a guest library reveal...

A phthalocyaninato zinc(II) dye with four peripheral N-methylpyridinium anchor groups and its higher-order complex with cucurbit[7] uril were photophysically characterised. The supramolecular host-guest interaction with the anchor yielded a deaggregation of the dye in neutral water solutions. This was signalised by the formation of a sharp UV-vis a...

Borylated arylisoquinolines with redshifted internal charge-transfer (ICT) emission were prepared and characterized. Upon heating, significant fluorescence quenching was observed, which forms the basis for a molecular thermometer. In the investigated temperature range (283–323 K) an average sensitivity of −1.2 to −1.8 % K−1 was found for the variat...

The encapsulation of odorants by synthetic receptor cucurbit[7]uril (CB[7]) reduces the response of olfactory receptors in Mozambique tilapia (Oreochromis mossambicus) in vivo. For example, the olfactory receptor response to the odorant adamantan-1-amine, as measured by electro-olfactography, was suppressed by 92% in presence of CB[7]. A reduction...

Aminonaphthalimide-BODIPY energy transfer cassettes were found to show very fast (kEET ≈ 10(10)-10(11) s(-1) and efficient BODIPY fluorescence sensitization. This was observed upon one- and two-photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison...

Die Natur verarbeitet Information durch chemische Reaktionen. Die Verbindung von chemischen Sensoren und Logik als Universalkonzept eröffnet Perspektiven für molekulare Informationsverarbeitung — auch weitab von biochemisch komplexen Systemen.

New C60 and C70 fullerene dyads formed with 4-amino-1,8-naphthalimide chromophores have been prepared by the Bingel cyclopropanation reaction. The resulting monoadducts were investigated with respect to their fluorescence properties (quantum yields and lifetimes) to unravel the role of the charge-transfer naphthalimide chromophore as a light-absorb...

The preparation of pH-switchable fluorescent borylated arylisoquinoline dyes via a flexible iridium-catalyzed route is reported. The obtained dyes feature aromatic amino substitution and lateral aliphatic amino groups as electron donors. The photophysical properties of the internal charge transfer dyes were studied, which was complemented by densit...

The function of a parity generator/checker, which is an essential operation for detecting errors in data transmission, has been realized with multiphotochromic switches by taking advantage of a neuron-like fluorescence response and reversible light-induced transformations between the implicated isomers.

A series of nine borylated arylisoquinolines with a systematic variation of electronic properties has been prepared and their photophysical properties have been investigated. The fluorescence color can be fine-tuned by the aryl moiety which is involved in internal-charge-transfer processes. For example, the methoxy-substituted 5 showed an intense g...

The use of photochromes for the implementation of molecular logic operations is a very promising approach toward molecular computing. This statement is based on a) the possibility of operating such molecular devices exclusively with photonic signals and b) spatiotemporally and remotely controlled switching, which is characteristic for photochromes....

Core-shell (CS) CdSe/ZnS quantum dots (QD) capped with ligands that possess a mercapto or an amino group and a naphthalimide (NI) as chromophore unit, linked by a short ethylene chain (CS@S-NI and CS@H2N-NI, respectively), have been synthesized and fully characterized by infrared and nuclear magnetic resonance spectroscopies, high-resolution transm...

The utility of supramolecular assemblies for the implementation of logic operations is briefly overviewed. The focus is on pseudorotaxanes, rotaxanes, and host–guest complexes with cyclodextrins and especially cucurbiturils. The discussion of systems that rely on metal–macrocycle interactions and hydrogen bonding completes this survey. Some of the...

A fluorophore-anchor dye based on the 4-amino-1,8-naphthalimide chromophore was designed and characterised with respect to its ability of forming supramolecular host–guest complexes with cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7) hosts. It was found that CB6 encapsulates the anchor of the dye with a high binding constant [K = (1.1–1.4) × 107 M...