Fluorescent aromatic sensors and their methods of use

Aromatic molecules that can be used as sensors are described. The aromatic sensors include a polycyclic aromatic hydrocarbon core with a five-membered imide rings fused to the core and at least two pendant aryl groups. The aromatic sensor molecules can detect target analytes or molecular strain as a result of changes in their fluorescence, in many cases with on-off behavior. Aromatic molecules that fluoresce at various frequencies can be prepared by altering the structure of the aromatic core or the substituents attached to it. The aromatic molecules can be used as sensors for various applications such as, for example, the detection of dangerous chemicals, biomedical diagnosis, and the detection of damage or strain in composite materials. Methods of preparing aromatic sensor molecules are also described

Doctor of Philosophy

dissertationPerylene tetracarboxylic diimide (PTCDI) derivatives, typical n-type organic semiconductors with high thermal- and photostability, have been extensively investigated for one-dimensional (1D) self-assembly and their applications in electronic and opto-electronic devices. Unfortunately, the intrinsically low electrical conductivity of PTCDI-based materials hinders further development of functions and applications. To solve this problem, covalently linked electron donor-acceptor (D-A) PTCDI molecules were designed, synthesized, and assembled into nanofibers in this work. Their electrical properties and the thermal- and photo-effects have been systematically studied. In addition to providing an improved understanding of the basic properties of the materials, these studies also open new and potential applications of the D-A PTCDI nanofibers. We designed a PTCDI molecule with 1-methylpiperidine (MP) substituted as electron donor to construct self-doped semiconductors, through one-dimensional (1D) self-assembly of the molecules into a nanofiber structure. The resultant nanofibers exhibit much higher conductivity than the other reported PTCDI molecules. The mechanism studies demonstrate that the MP moieties reduce the adjacent PTCDI core into an anionic radical, which acts as the n-type dopant in the PTCDI lattice. Such highly conductive nanofiber materials can be used as chemiresistive sensor for vapor detection of hydrogen peroxide. Our further study on the MP-PTCDI nanofibers reveals a persistent photoconductivity (PPC) effect, which is sustained conductivity after light illumination is terminated. Systematic study demonstrates the PPC effect is predominantly caused by the D-A structure of PTCDI. This study helps understand the PPC mechanism, and guide the design of new material structures for sustained charge separation to further enhance the photovoltaic and photocatalytic efficiency of organic semiconductor materials. Thermoactivated conductivity was studied in the nanofiber materials assembled from other two D-A PTCDI molecules both in the dark and under visible light illumination. A symmetric n-dodecyl side chain substituted PTCDI nanofiber was used as a control for the comparative study. The charge transport properties are strongly dependent on the PTCDI molecular structure and packing states within the nanofibers. The comprehensive understanding of the thermoactivated conductivity in PTCDI nanofibers can assist in designing new D-A molecules that can be fabricated into nanofibers to be used as temperature sensor with increased sensitivity

Recent advances in perylene diimide-based active materials in electrical mode gas sensing

This review provides an update on advances in the area of electrical mode sensors using organic small molecule n-type semiconductors based on perylene. Among small organic molecules, perylene diimides (PDIs) are an important class of materials due to their outstanding thermal, chemical, electronic, and optical properties, all of which make them promising candidates for a wide range of organic electronic devices including sensors, organic solar cells, organic field-effect transistors, and organic light-emitting diodes. This is mainly due to their electron-withdrawing nature and significant charge transfer properties. Perylene-based sensors of this type show high sensing performance towards various analytes, particularly reducing gases like ammonia and hydrazine, but there are several issues that need to be addressed including the selectivity towards a specific gas, the effect of relative humidity, and operating temperature. In this review, we focus on the strategies and design principles applied to the gas-sensing performance of PDI-based devices, including resistive sensors, amperometric sensors, and operating at room temperature. The device properties and sensing mechanisms for different analytes, focusing on hydrazine and ammonia, are studied in detail, and some future research perspectives are discussed for this promising field. We hope the discussed results and examples inspire new forms of molecular engineering and begin to open opportunities for other rylene diimide classes to be applied as active materials

Doctor of Philosophy

dissertationOrganic donor-acceptor (D-A) interaction has attracted intensive research interest because of the promising applications in electronic devices and renewable energy. Depending on the interaction process, the optoelectronic properties of organic semiconductors may change dramatically. To improve their performance and expand the applications, we have investigated the structure-property relationship in D-A cocrystals and nanofibril composites. These materials provide unique D-A interface structures, thus allowing tunable charge transfer across the interface, which can be modified and controlled by exquisite molecule design and supramolecular assembly. In Chapter 2, we studied the fabrication, conductivity, and chemiresistive sensor performance of tetrathiafulvalene (TTF) - 7,7,8,8-tetracyanoquinodimethane (TCNQ) charge transfer cocrystal microfibers. Compared to TCNQ and TTF, TTF-TCNQ cocrystal has much higher conductivity under ambient conditions, due to the high yield of charge separation, which also induces high polarization at the interface, resulting in different binding intensity towards alkyl and aromatic amines. Based on this investment, we developed a TTF-TCNQ chemiresistive sensor to efficiently discriminate alkyl and aromatic amine vapors. In Chapter 3, we further designed a new series of D-A cocrystals, and studied the coassembly and optical properties. The cocrystal is composed of coronene and perylene diimide at 1:1 molar ratio and belongs to the triclinic system, as confirmed by X-ray analysis. The donor and acceptor molecules perform an alternate π-π stacking along the (100) direction, leading to the strong one-dimensional growth tendency of macroscopic cocrystal. Additionally, due to the charge transfer interaction, the cocrystal shows a new and largely red-shifted photoluminescence band, compared to the crystals of the components. In Chapter 4, we alternatively developed a series of donor-acceptor nanofibril composites, in which the donor and acceptor nanofibers become the building blocks. By changing the side chains into alkyl groups, the composite forms a homogeneous film with a large donor-acceptor interface and favorable photoinduced charge transfer, leading to a high photoconductivity enhancement, which is a three order magnification of the photoconductivity of the donor and acceptor nanofibers. Furthermore, our measurement proved the D-A interface with alkyl chains interdigitating is compatible and tunable to external alkane vapors, making the composite suitable for chemiresistive sensors for alkane detection

Physisorption of perylene dyes on graphite​

This thesis work was carried out at CNR of Bologna. CNR- ISOF (Institute of Organic Synthesis and Photoreactivity) in the group of Dr. Vincenzo Palermo. The aim of this thesis was to perform a comparative and quantitative study on the interaction of three different PDI (perylene diimide) dyes with graphene (G) sheets in solution, using a phenomena called “dye’s capturing”. The only difference between the PDI dyes tested was the terminal atom in the side groups. In particular, we used a perylene core with side ethyl-phenyl group exposing in the para position a hydrogen (PDI-H), fluorine (PDI-F), or chlorine atom (PDI-Cl). Although the relative simplicity of the process and the measurement itself, the preparation of a reliable experimental setup is not trivial and several issues had to be taken into account. The main challenges to be overcame were related to the effective stability and reliability of the chemical systems, such as dyes, solution and graphite during the entire exposure time. For this reasons the work addressed the following issues: 1)Studying the interaction of small organic molecules and graphite flakes, using commercial products. 2)Finding the best conditions for the dye capturing process (concentration, stabilization of the solution, solvent etc.).3)Understanding of the “dye’s capturing” phenomena by UV-VIS and fluorescence techniques. 4)Stabilizing a relationship between the chemical structure of PDI-X (with side chains symmetrically terminated with a different atom) and the interaction with graphite, taking into account adsorption speed, packing, etc. 5)After testing the samples, the reported results were used to: 1) Determinate the best suitable molecule for the dye capturing process, and optimize a hypothetical industrial process by calculating the surface area for each molecule. 6)Morphology and structural characterizations with different technique like: AFM, SEM, EDX, XRD, fluorescence microscopy, TGA/DSC, IR

Flower-like supramolecular self-assembly of phosphonic acid appended naphthalene diimide and melamine

Diverse supramolecular assemblies ranging from nanometres to micrometers of small aromatic π-conjugated functional molecules have attracted enormous research interest in light of their applications in optoelectronics, chemosensors, nanotechnology, biotechnology and biomedicines. Here we study the mechanism of the formation of a flower-shaped supramolecular structure of phosphonic acid appended naphthalene diimide with melamine. The flower-shaped assembly formation was visualised by scanning electron microscope (SEM) and transmission electron microscopy (TEM) imaging, furthermore, XRD and DLS used to determined mode of aggregation. Characteristically, phosphonic acid-substituted at imide position of NDIs possess two important properties resulting in the formation of controlled flower-like nanostructures: (i) the aromatic core of the NDI which is designed to optimize the dispersive interactions (π-π stacking and van der Waals interactions) between the cores within a construct and (ii) phosphonic acid of NDI interact with malamine through molecular recognition i.e. strong hydrogen-bonding (H-bonding). We believe such arrangements prevent crystallization and favour the directional growth of flower-like nanostructure in 3D fashion. These works demonstrate that complex self-assembly can indeed be attained through hierarchical non-covalent interactions of two components. Furthermore, flower-like structures built from molecular recognition by these molecules indicate their potential in other fields if combined with other chemical entities

Fluorescent probes and nanostructured materials for the detection of environmental toxins and catalysts development

La tesis trata sobre la síntesis y utilización de materiales modificados, para el reconocimiento de distintas sustancias por fluorescencia o para el desarrollo de catalizadores de reacciones orgánicas de interés. En la primera parte de la tesis se desarrollaron sensores de sustancias tóxicas como mercurio (II) y plomo (II), midiendo en muestras de pescado y disolución respectivamente. Por otro lado, se perfeccionó un sensor para la detección de TATP en fase gas, explosivo sin uso militar utilizado en ataques terroristas. Además, y en complemento a lo anterior, se trabajó con sensores para detectar toxinas alimentarias como la cereulida, o moléculas de interés biológico/toxicológico como el monóxido de carbono. En una segunda parte, se modificaron una serie de materiales con partículas metálicas de oro o paladio para la catálisis de reacciones orgánicas de importancia en la industria; presentando ventajas como ser reciclables, alto rendimiento de reacción y gran selectividad en los productos.The topic of the thesis was the synthesis and modification of materials, for the detection of different substances by fluorescence or to the development of new catalysts for organic reactions. Several probes were developed for the detection of toxic substances such as mercury (II) or lead (II), measuring their presence in fish samples or in solution, respectively. In addition, Silica-Based materials were modified in order to the detect TATP in vapour phase, an explosive with no military use and employed in terrorist attacks. Furthermore, other probes were synthesized and tested for other analytes, such as food toxins (cereulide) or molecules with biological/toxicological interest, such as carbon monoxide. In the second part of the thesis, polymeric materials were modified with gold or palladium metallic particles and employed for the catalysis of organic reactions with industrial importance, presenting several advantages over traditional catalyst

Nanoscaled Fluorescent Films and Layers for Detection of Environmental Pollutants

Hazardous gas and ion pollutants are the most serious environmental problems around the world. It is of great importance to develop devices for easy detection of these hazardous substances. Fluorescence technology with high resolution and operational simplicity has attracted a lot of attention in recent years. Organic fluorescent dyes absorb/emit lights within a broad wavelength range, which is suitable for various demands. Chromophores, such as perylene, cyanine dyes, spiropyran, and so on, are widely studied as fluorescent probes for gases and ions. The dyes could respond to external stimuli through structural changes of the conjugated chromophore itself or the attached functional groups, leading to detectable spectral changes. Organic dyes are incorporated into nanoscaled films and layers, which are portable and durable for effective sensing in complex environments. In this chapter, preparation and application of fluorescent films and layers (FFL) for gaseous/ionic detection are reviewed. We discuss the response mechanism of fluorescent dyes, the fabrication of nanoscaled FFL, and some examples of FFL for the detection of gas and ion pollutants

The design and study of porous metal organic framework (MOF) structures

Metal Organic Frameworks are hybrid materials that can be modified by altering their fundamental components. This capability enables them to be tailored to suit specific applications, which range from catalysis to sensor technologies. Sensor based materials using MOFs technology have received a great deal of interest over recent years due to the potential advantages they offer with regard to monitoring devices. Therefore, in this project we attempted to systematically design and synthesise porous solid-state MOFs sensors using charge transfer (CT) phenomena as a basis for its “sensory” abilities. CT host molecules/MOF linkers used in this work were based on pyromellitic diimide derivatives. These host molecules contain electrophilic as well as trans arranged carboxylic acid components, which allows the formation of CT complexes through CT π···π interactions and extended hydrogen bonding or metal coordination through the carboxylic acids. Two pyromellitic linkers were synthesised through condensation reactions, namely N,N’-bis(glycinyl)-pyromellitic diimide (gly-L) and N,N’-bis(γ-aminobutyric)-pyromellitic diimide (but-L). The smaller gly-L host successfully formed CT complexes with all four aromatic hydrocarbons used in the work (naphthalene, anthracene, phenanthrene and perylene), whereas the larger but-L ligand selectively formed two novel CT complexes with phenanthrene and perylene. All CT complexes obtained crystallised in the triclinic P-1 crystal system with the exception of gly-ANT (gly-L + anthracene) and but-PERY (but-L + perylene). The aromatic hydrocarbons formed 1:1 molecular complexes with each host molecule, thereby forming a stacked 2D layer. A R4 4(12) hydrogen bonding pattern was observed in the gly-ANT structure due to the incorporation of two solvent methanol molecules within the carboxylic acid bridges, whereas all other CT complexes formed conventional R2 2(8) dimers. Besides gly-ANT and but-PERY, all CT complexes form 2D parallel sheets with stabilisation in the third dimension achieved by various intermolecular CH···O hydrogen bonding interactions between the host-host and hostguest molecules. Lattice energy calculations using Gavezzotti’s OPIX program suite were used to find common molecular arrangments as well as the relative stability of these arrangments in all the CT complexes. These included π···π stacking, and various hydrogen bond interactions. Various analysis techniques (X-Ray, thermal and spectroscopical) were employed to further assess the physical properties of these materials. The trans arranged carboxylic acid groups of the CT host/linker molecules are somewhat unusual when compared to the usual linear linker approach utilised in MOF production. Both host linker molecules were utilised in MOF formation, however under the same synthetic conditions, gly-L showed an affinity to MOF formation, producing four new structures, whereas but-L did not. The use of divalent zinc and cadmium nitrates produced large MOF crystals at room temperature, while a cobalt (II) nitrate reaction mixture had to be cooled down to produce suitable crystals. SCXRD was successfully utilised to identifying the structural topology and bonding interactions of each MOF. All metals used in this study, adopted typical coordination environments for d-block metals, with each structure containing solvent molecules within its unit cell. Solvent molecules play a vital role in the overall extension of the each structure through various hydrogen bonding interactions. With the exception of one zinc based MOF structure (MOF-Zn2), all structures contain bridging linkers that enable two dimensional extension leading to herringbone (MOF-Zn1) and step-like arrangements (MOF-Cd1 and MOF-Co1). The bonding characteristics and structural features of gly-L linker component were retained within all the MOF frameworks. Of the four structures obtained, only MOF-Zn2 and MOF-Cd1 formed 1D open pores of 56Å3 and 29Å3 respectively. Unfortunately due to structural instability and poor yields further inroads into MOFs with linkers using CT complexing for sensory capabilities could v not be achieved. This project illustrates many of the concepts and thoughts into applying rational design to the synthesis of functional MOF materials and the many problems associated with such studies

Organic photosensitizers for light-driven hydrogen evolution: synthesis, characterization and application

This work utilizes organic chromophores, namely perylene dyes and BODIPYs, as light-active component in light-driven hydrogen evolution