Porphyrin-Based Nanostructures for Sensing Applications

The construction of nanosized supramolecular hosts via self-assembly of molecular components is a fascinating field of research. Such intriguing class of architectures, beside their intrinsic intellectual stimuli, is of importance in many fields of chemistry and technology, such as material chemistry, catalysis, and sensor applications. Within this wide scenario, tailored solid films of porphyrin derivatives are structures of great potential for, among others, chemical sensor applications. The formation ofsupramoleculesrelays on noncovalent interactions (electrostatic, hydrogen bond, , or coordinative interactions) driven by the chemical information stored on the assembling molecules, such as shape and functional groups. This allows, for example, the formation of large well-defined porphyrin aggregates in solution that can be spontaneously transferred onto a solid surface, so achieving a solid system with tailored features. These films have been used, covering the bridge between nanostructures and microsystems, for the construction of solid-state sensors for volatiles and metal ion recognition and detection. Moreover, the variation of peripheral substituents of porphyrins, such as, for example, chiral appended functionalities, can result in the formation of porphyrin aggregates featuring high supramolecular chirality. This would allow the achievement of porphyrin layers characterised by different chiroptical and molecular recognition properties

Proline Enantiomers Discrimination by (L)-Prolinated Porphyrin Derivative Langmuir–Schaefer Films: Proof of Concept for Chiral Sensing Applications

A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air–pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air–subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10−5 M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir–Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers

Proline enantiomers discrimination by (L)-prolinated porphyrin derivative Langmuir-Schaefer films: proof of concept for chiral sensing applications

A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air-pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air-subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10(-5) M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir-Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers

Design of Novel Classes of Building Blocks for Nanotechnology: Core‐Modified Metalloporphyrins and Their Derivatives

Metalloporphyrins and related macrocycles have been of great interest due to their role in biology and their numerous technological applications. Engineering of the porphyrins by replacing pyrrole nitrogens with other elements is a highly promising approach for tuning properties of porphyrins. To date, numerous efforts have been made to the modification of the porphyrin core with main‐group elements, such as chalcogens (O, S, Se) and phosphorus. Thus, the modification of the porphyrin core by incorporation of heteroatoms instead of nitrogens is a very promising strategy for obtaining novel compounds with unusual optical, electrochemical and coordinating properties as well as reactivity. These novel compounds can be used as building blocks in various nanotechnological applications. Within the framework of this research, the following questions can be formulated: (i) what structures will core‐modified porphyrins adopt? (ii) How will electronic properties of core‐modified porphyrins differ from those of common tetrapyrroles? (iii) Will the core‐modified porphyrins be able to form stacks and other arrays like regular porphyrins? (iv) Can core‐modified porphyrins form complexes with fullerenes? (v) Can core‐modified porphyrins activate small molecules, e.g. O2 or N2? (vi) Will the core‐modified porphyrins be able to form complexes with nanoparticles

Recent advances in chemical sensors using porphyrin-carbon nanostructure hybrid materials

Porphyrins and carbon nanomaterials are among the most widely investigated and applied compounds, both offering multiple options to modulate their optical, electronic and magnetic properties by easy and well-established synthetic manipulations. Individually, they play a leading role in the development of efficient and robust chemical sensors, where they detect a plethora of analytes of practical relevance. But even more interesting, the merging of the peculiar features of these single components into hybrid nanostructures results in novel materials with amplified sensing properties exploitable in different application fields, covering the areas of health, food, environment and so on. In this contribution, we focused on recent examples reported in literature illustrating the integration of different carbon materials (i.e., graphene, nanotubes and carbon dots) and (metallo)porphyrins in heterostructures exploited in chemical sensors operating in liquid as well as gaseous phase, with particular focus on research performed in the last four years

Heterostructures Based on Porphyrin/Phthalocyanine Thin Films for Organic Device Applications

Multilayer or blend heterostructures based on porphyrins and phthalocyanines were obtained on different substrates using VTE and MAPLE methods. Stacked structures based on ZnPc and C60 with NTCDA were prepared by VTE on ITO/glass, their current value being increased by the deposition of the materials in an inverted configuration or by using ITO/PEDOT:PSS as a substrate. Multilayer structures comprising ZnPc and NTCDA were fabricated by MAPLE on an AZO/glass. Treating the AZO in oxygen plasma, a higher current value was obtained for the deposited heterostructures. The oxygen plasma treatment can increase the work function of the AZO resulting in a decrease of the energetic barrier from AZO/organic interface and finally improving the charge transport. Stacked layers or blend heterostructures having ZnPc, MgPc and TPyP were deposited by MAPLE on ITO/PET. In the case of those containing MgPc and TPyP, an increase in the current value (in dark) was obtained for the blend compared to the stacked layer configuration. For those with ZnPc and TPyP, under illumination, a photovoltaic effect was observed for the blend structure. All heterostructures are featured by a large absorption in the visible domain of the solar spectrum and suitable electrical properties for their use in OPV applications

Electrochemistry and STM-assisted Molecular electronics study of bimetallic hexaphyrins

ELECTROCHEMISTRY AND STM-ASSISTED MOLECULAR ELECTRONICS STUDY OF BIMETALLIC HEXAPHYRINS. The electron transport in porphyrinoids are related to several bioprocesses in Nature, from conversion from solar energy to chemical energy in photosynthesis to the transport and reduction of oxygen in aerobic animals. Due to these characteristics, several bioinspired applications have used this class of materials, photovoltaics, water splitting, catalysis and photodynamic therapy. To further understand how this process occurs in expanded porphyrins, 5 hexaphyrins in Hückel aromaticity were synthesized, with and without metal centres. These molecules were characterized by spectroscopy, electrochemistry and through molecular break junctions. The absorption spectrum of hexaphyrins show several possibly transitions, which splits and broadens with the addition of metal centres due to the degeneration of the molecule’s orbitals. The spectroscopic band gap was characterized by fluorimetry showing a gap between 1.12 to 1.20 eV for the molecules synthesized. Electrochemistry measurements shows several distinct quasi-reversible redox pairs. The addition of metal centres shifted the processes accordingly to the electronegativity of the metal centres. Due to the severe number of reactions a diagnosis criterium was developed to indicate which peaks corresponds to reactions in the macrocycle or its ligands and which are likely to occur on the metal centres. The molecular conductance of the hexaphyrins were studied with STM assisted break junctions on non-modified and modified gold as electrodes. The gold modification was proved necessary due to the lack of interactions between the molecules and the metal electrodes. Several current signatures were observed on 4-TPy modified gold. This corresponds to all possible molecular junction conformations. Upon the addition of metal centres, a similar trend is observed for each metal, indicating that the molecule properties do not impact as much as the conformation of the molecular wire.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)ELECTROCHEMISTRY AND STM-ASSISTED MOLECULAR ELECTRONICS STUDY OF BIMETALLIC HEXAPHYRINS. O transporte eletrônico em porfirinoides está relacionado com diversos bioprocessos na Natureza, da conversão de energia solar em energia química na fotossíntese ao transporte e redução de oxigênio em animais aeróbicos. Devido à essas características, diversas aplicações bioinspiradas utilizam essa classe de materiais, como fotovoltaicos, water splitting, catalisadores e terapia fotodinâmica. Para compreender como esses processos ocorrem em porfirinas expandidas, cinco hexafirinas foram sintetizadas em aromaticidade de Hückel, com e sem centros metálicos. Estas moléculas foram caracterizadas por técnicas espectroscópicas, eletroquímicas e por junções moleculares. Os espectros de absorção dessas hexafirinas mostram diversas transições possíveis, nas quais os desdobramento e alargamento das bandas com a adição de centros metálicos estão correlacionados com o a degeneração dos orbitais moleculares da molécula. O band gap espectroscópico foi caracterizado através de fluorimetria, elucidando um gap entre 1.12 e 1.20 eV. As medidas eletroquímicas mostram diversos processos quasi- reversíveis. A adição de centros metálicos desloca os potenciais dos processos redox de acordo com a eletronegatividade do metal adicionado. Devido ao grande numero de processos observados, um critério de diagnóstico foi desenvolvido para indicar quais processos ocorrem no centro metálico e quais processos ocorrem no macrociclo do material e seus ligantes. A condutância molecular das hexafirinas foram medidas através de junções moleculares assistidas por um STM, sob substratos de ouro. A funcionalização do ouro se mostrou necessária para observar os processos devido à falta de interações entre as moléculas e os eletrodos metálicos. Diversas “current signatures” foram observadas quando o ouro foi modificado com 4-TPy. Isto corresponde a cada possível conformação de junção molecular. Com a adição de centros metálicos, um comportamento similar pode ser observado de acordo com cada metal adicionado, indicando que as propriedades da molécula não influenciam a sua condutância tanto quanto a geometria do fio molecular.FAPESP: processo 2016/05363-

Supramolekulární komplexy oxoporfyrinogenů s organickými molekulami

Title: Supramolecular complexes of oxoporphyrinogens with organic molecules Author: Václav Březina Department: Department of Macromolecular Physics Supervisor: doc. RNDr. Lenka Hanyková, Dr., Department of Macromolecular Physics Abstract: Oxoporphyrinogens are flat macrocyclic molecules possessing binding and protonation sites, and capable of light absorption in the visible region. These properties are prerequisites for a colori- metric molecular sensor, i.e. a specific detector of other molecules in the sample. In this work, we studied chromic properties of three oxoporphyrinogens, OxP and its partially (Bz2OxP) and fully (Bz4OxP) N-benzylated derivatives. Their colorimetric response to organic acids is caused by protonation and subsequent formation of supramolecular host-guest complex. We have shown that colorimetric sensitivity is highest for OxP and gradually weakens for Bz2OxP and Bz4OxP since the N-benzylation blocks the central binding sites, decreasing binding affinity of the ox- oporphyrinogens. Furthermore, solvatochromic response of the oxoporphyrinogens to varying solvent polarity showed similar sensitivity decrease in Bz2OxP and Bz4OxP. The chromic and binding properties were studied by UV/vis and NMR spectroscopy, host-guest binding models were applied to describe the formation of...Oxoporfyrinogeny, ploché makrocyklické molekuly, na sebe dokáží navázat kyseliny či jiné látky a zároveň pohlcují světlo ve viditelném oboru. Tyto vlastnosti jsou předpokladem pro molekulární kolorimetrický senzor, detekující přítomnost konkrétních látek ve vzorku. V této práci jsme studovali chromismus tří oxoporfyrinogenů, OxP a jeho částečně (Bz2OxP) a úplně (Bz4OxP) N-benzylovaných derivátů. Jejich kolorimetrická odezva na organické kyseliny je způsobena protonací a následnou tvorbou supramolekulárního "host-guest" komplexu. Vysoká citlivost OxP na přítomnost kyseliny se postupně snižuje u Bz2OxP a Bz4OxP, neboť N-benzylace blokuje centrální vazebná místa a tím se snižuje vazebná afinita oxoporfyrinogenů. Kromě toho byla pozorována solvatochromická odezva oxoporfyrinogenů na měnící se polaritu rozpouštědla, kde se ukázala podobně snížená citlivost u Bz2OxP a Bz4OxP. Ke studiu chromismu a vazebných vlastností byly použity UV/vis a NMR spektroskopie, tvorba komplexů oxoporfyrinogen-kyselina byla popsána vazebnými modely typu "host-guest". Přítomnost chemické výměny v NMR spektrech protonovaného OxP a Bz2OxP ukázala na přítomnost několika dynamických procesů, mimo jiné prototropní tautomerizace (tj. změna místa protonace) nebo rotace objemných postranních skupin v Bz2OxP. Tyto procesy byly v NMR...Department of Macromolecular PhysicsKatedra makromolekulární fyzikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult