Photochemistry for Molecules, Sensors and Materials
1. ESIPT compounds
Synthesis and photophysical characterization of compounds able to Excited State Intramolecular Proton Transfer (ESIPT) process, which is a photochemical process that produces a tautomer with a totally different electronic structure from the initial ground state conformer. This process has been extensively investigated in the past decades due to its importance in chemistry, biology, and biochemistry. In these compounds, the driving force for ESIPT is the redistribution of the electron density in the excited state, where the donor group (phenol or aniline scaffold) is significantly more acidic and the acceptor group (imino/azo nitrogen- or carbonyl-oxygen-containing ring skeleton) more basic, thereby enhancing proton transfer at a faster rate relative to the ground state. The ESIPT mechanism can generally be found in flavonols, chromones, and benzazoles structures. The AOP Research Group presents the expertise to design and characterize new ESIPT compounds for a wide range of applications.
2. Photophysical characterization of small organic compounds
The AOP Research Group synthesizes new photoactive heterocycles using described synthetic methodologies or developing new ones. In this way, we are able to obtain several different organic compounds, such as benzazoles, cyanines, squaraines, functionalized indoles, and different supramolecular scaffolds. These compounds can present absorption and fluorescence emission in the UV-Vis region up to the NIR regions. The synthesized heterocycles can present different electronic conjugation, as well as different organic groups (EWG and EDG), allowing these compounds to be envisaged as potential optical sensors for anions or macromolecules in solution, as photoactive monomers to produce new polymeric materials, or as modified silica in order to prepare new fluorescent hybrid materials. In addition, the AOP Research Group also collaborates with well-established organic synthesis groups to help them to better understand electronic properties on the ground and the excited states of their compounds.
3. Optical sensing
The development of fluorescent sensors has been a subject of great interest in the field of chemistry, biology, and materials science. The design of a sensor must take into account two main parts: the recognition and signaling units, which should act in synergy. Upon exposition to an analyte, the resulting interaction should result in changes in the photophysical profile which can be measured and then result in useful analytical information. The recognition moiety is responsible to perform specific interactions with the analyte, causing a change in the system, while the signaling moiety is a fluorophoric unit that will send an optical signal in response to this perturbation in the system. The AOP Research Group presents the expertise to design and study as optical sensors, several fluorophores upon biomacromolecules (HSA, BSA, DNA), anionic and cationic species, enantiomers, pH, organic vapors, and so on.
The field of organic electronics comprises versatile materials for the development of light-emitting diodes with the possibility of a wide range of color emissions depending on the designed electronic molecular structure and consequent device cell. In this context, tremendous effort has been focused on the development of white organic light-emitting diodes (WOLEDs) due to the increasing urgency for renewable and sustainable light sources and new technological applications for the design of flat and flexible displays. In this sense, the AOP Research Group collaborates with well-established research groups to prepare solution-processable devices that are a suitable and practical alternative for the white-light generation of organic diodes.
5. Supramolecular photochemistry
The influence of confined media on the photophysical properties of the fluorophores has been investigated in recent years, where usually a confined medium allows selectivity in a chemical or photochemical reaction by increasing rate constants, or even suppressing most favored pathways, which are present in solution. Thus, the study of inclusion complexes in supramolecular capsules can afford information on proton transfer and energy transfer, or even about the bond rotation of molecular guests that could lead to new physicochemical properties when confined than free in solution. Thus, several organic hosts have been presented in the literature, including micelles, dendrimers, cucurbiturils, calixarenes, and cyclodextrins. In this sense, the AOP Research Group presents the expertise to study different fluorophores (Guest) in confined media (Host) to investigate their excited state behavior in highly restricted environments using steady-state and time-resolved fluorescence emission techniques.
6. Photoactive materials by sol-gel process
Organic-inorganic materials are usually classified into three major groups: (i) intercalation compounds, (ii) organic derivatives of inorganic solids, and (iii) sol-gel hybrid materials. This latter is usually used for all types of hybrid materials and depends on the nature of the interaction between organic and inorganic components. Their organization at micro and nanometric scales, as well as the respective properties that can be envisaged for these materials, showed to be dependent on the chemical properties of their organic and inorganic components, and also notably dependent on the interaction between them. It can be found in the literature that the nature of these interactions categorizes these materials in two main different classes. The materials where no covalent or iono-covalent bonds are present between the components, such as hydrogen bonding, van der Walls forces, π-π interactions, or electrostatic forces, are defined as type I (or class I) hybrid materials. On the other hand, type II (or class II) hybrid materials present at least a fraction of the organic and inorganic components linked through strong chemical bonds (covalent, iono-covalent, or Lewis acid-base pairs). Therefore, type II hybrid materials obtained by the sol-gel process are a quite interesting class of materials, allowing the combination of organic moieties with inorganic hosts, that can be achieved through covalent grafting of organic photoactive compounds or by copolymerization of silica precursors. Thus, hybrid materials have attracted great interest over the past decades, where the design and synthesis of these materials emerged from the expectation that synergetic integration could take place. In this sense, the AOP Research Group presents the expertise to design different type II photoactive hybrid materials for a wide range of applications.