Light-induced reorientation and birefringence in polymeric dispersions of nano-sized crystals

Nanocrystals (50-250 nm) of a Palladium complex within a polyisobutylmethacrylate matrix were prepared by a phase separation method. In these dispersions, a light-induced birefringence with Deltan approximately 10(-3) was induced, without the application of an electric field. This effect was related to the photoconducting properties of the dispersion. Evidence for charge photogeneration without any applied field was obtained. The photorefractive behaviour of the material confirmed that the nanocrystals reorientation is a consequence of photoconducting properties. A light-generated electric field approximaely E 3 V/microm was estimated. These results illustrate the potential of materials with a nano-crystalline dispersion morphology as light-responsive media

Photoconductive properties and electronic structure in 3,5-disubstituted 2-(2′-pyridyl)pyrroles coordinated to a Pd(II) salicylideneiminate synthon

The synthesis and the electrochemical, photophysical, structural, and photoconductive properties of three new heteroleptic Pd(II) complexes with various 3′,5′- disubstituted-2-(2′-pyridil) pyrroles H(N^N) as coordinated ligands are reported. The coordination of the metal center was completed by a functionalized Schiff base H(O^N) used as an ancillary ligand. The [(N^N)Pd(O^N)] complexes showed highly interesting photoconductive properties which have been correlated to their electronic and molecular structures. Theoretical density functional theory (DFT) and time-dependent DFT calculations were performed, and the results were confronted with the organization in crystalline phase, allowing to point out that the photoconductive properties are mainly a consequence of an efficient intramolecular ligand-to-metal charge transfer, combined to the proximity between the central metal and the donor moieties in the solid-state molecular stacks. The reported results confirm that these new Pd(II) complexes form a novel class of organometallic photoconductors with intrinsic characteristics suitable for molecular semiconductors applications.Supported by Ministero dell’Istruzione, dell’Universitàe della Ricerca by the ELIOTROPO.Peer reviewe

Synthesis and characterization of new hybrid organic/inorganic materials for electro-optic applications

Doctorate in Science and Technologies of Mesophases and Molecular Materials,XXIII Ciclo,a.a.2010Università della Calabri

Gallium coordination compounds as multifunctional materials. Synthesis, characterization and properties

International Doctorate in Science and Technology of the Mesophases and of the Molecular Materials, Ciclo XIX a.a. 2003-2006Università degli Studi della Calabri

Novel molecular materials for photo/electro conversion based on Palladium and Iridium organometallic complex

Scuola di Dottorato "Bernardino Telesio", Mesofasi e Materiali Molecolari Molecolari, Ciclo XXVI,a.a. 2013Questo lavoro di ricerca è dedicato allo sviluppo di nuovi materiali molecolari basati su complessi ciclometallati di Pd(II) e di Ir(III) per la foto/elettro conversione. Negli ultimi quindici anni, al fine di ottenere dispositivi più flessibili, più leggeri e più facilmente processabili, sono stati studiati principalmente materiali a base organica. Tali materiali presentano però, proprio a causa della loro natura organica, molteplici svantaggi, tra i quali scarsa qualità delle interfacce formate, limitata stabilità chimico-fisica in fase di funzionamento del dispositivo, difficile trasporto di carica, scarso assorbimento nel visibile e basse efficienze di luminescenza. Al fine di migliorare le prestazioni finali dei dispositivi elettro-ottici, è stata introdotta una nuova classe di materiali che utilizza come specie attive i composti organometallici. Nell’ambito di questo lavoro di tesi, sono stati sintetizzati nuovi complessi organometallici di Pd(II) e Ir(III) e ne sono state studiate le proprietà chimico-fisiche alla base dello sviluppo di materiali efficienti per la foto/elettro conversione. La prima parte del lavoro di tesi ha riguardato la preparazione di complessi per la conversione dell’energia solare. In particolare sono stati sintetizzati e caratterizzati nuovi complessi fotoconduttori ciclopalladati di Rosso Nilo, contenenti basi di Schiff opportunamente funzionalizzate come leganti ancillari. Inizialmente si è scelto di utilizzare il colorante Rosso Nilo come legante ciclometallante per le sue ottime proprietà di assorbitore di luce visibile. Il suo utilizzo ha inoltre comportato, nei complessi ottenuti, anche la separazione fisica su scala molecolare degli orbitali di frontiera HOMO e LUMO. In particolare i due orbitali risultano essere prevalentemente localizzati su due diversi frammenti molecolari. Tale separazione induce un efficiente processo di fotogenerazione che è alla base delle ottime proprietà di fotoconduzione osservate per questa classe di composti in un ampio intervallo di lunghezze d’onda. Per finalizzare l’utilizzo di complessi ciclopalladati di Rosso Nilo a specifiche applicazioni optoelettroniche, sono stati introdotti opportuni gruppi funzionali sia sul legante ciclometallante che sul legante ancillare In particolare i nuovi gruppi funzionali hanno permesso di : i) indurre proprietà mesomorfiche caratterizzate da un ampio grado di ordine in un grande intervallo di temperature e di ottenere così una nuova classe di metallomesogeni fotoconduttori; ii) aumentare la solubilità dei complessi preparati rendendo possibile il loro utilizzo unitamente al PC61BM, nella costruzione di celle solari ad eterogiunzione dispersa; iii) preparare, tramite il processo di elettropolimerizzazione, film sottili fotoconduttori di elevata qualità su elettrodi modificati; iv) poter ancorare i complessi sintetizzati a substrati di TiO2 e costruire celle solari di tipo Dye Sensitized (DSSCs). La seconda parte del lavoro di tesi, ha invece riguardato, la sintesi e la caratterizzazione fotofisica ed elettrochimica di complessi di Ir(III) per lo sviluppo di dispositivi elettroluminescenti. Sebbene esista in letteratura un elevato numero di esempi di complessi cationici di Ir(III) solamente pochi complessi anionici di Ir(III) sono stati descritti finora. Inoltre, i pochi esempi riportati, contengono leganti ancillari monodentati che rendono tali complessi chimicamente instabili all’interno di dispositivi elettroluminescenti. Al fine di ampliare la classe di composti anionici di Ir(III) esistenti e di migliorane la stabilità chimica, sono stati sintetizzati nuovi complessi anionici aventi leganti ancillari bidentati di tipo catecolato e orotato. E’ stata inoltre preparata e caratterizzata una nuova serie di “soft salt” di Ir(III) contenenti i nuovi complessi anionici ottenuti accoppiati ad opportuni complessi cationici di Ir(III) già noti in letteratura. Sono stati infine preparati e caratterizzati nuovi complessi luminescenti neutri di Ir(III) elettropolimerizzabili. Utilizzando tali complessi sono stati anche ottenuti film sottili elettrogenerati di alta qualità.Università della Calabria XXVI SSD CHIM/03a.a. 201

Hydrophilic Ir(III) complexes suitable for the construction of functional mesoporous materials

Dottorato di Ricerca in Scienze e Tecnologie delle Mesofasi e dei Materiali Molecolari, XXV Ciclo, a.a. 2011-2012Nowadays, intensive efforts have been carried out on the design of novel advanced molecular materials, which can self-assemble in a strong, directional and reversible way to construct supramolecular materials with specific properties. The rational design and preparation of supramolecular assemblies through the coordination of metal ions with organic ligands has attracted attention for developing novel crystalline materials with interesting structural topologies and promising applications, and has evolved as an interesting research. The metals used in these complexes can serve as structural components and/or as a source of properties (e.g., magnetic, catalytic, optoelectronic, etc). Cyclometallated Ir(III) octahedral complexes possess fascinating properties used in various applications such as luminescent and electrochemiluminescent labeling reagents for biological substrates1, sensors2, or electronic devices3,4. Recently, the interest in ionic Ir(III) complexes is growing rapidly because not only high internal quantum efficiency (~100%) can be achieved in principle, but also tunable emission wavelengths over the entire visible spectrum can be successfully obtained through ingenious modification of ligands. In particular, Ir(III) complexes based on the chelating ligand 2,2’-bipyridine (bpy) have been successfully applied in light-emitting electrochemical cells (LECs) and sensors.5 The theoretically calculated phosphorescence yield (Fp) of the Ir(III) complexes are close to unity in solution.6 The solution investigations have made great contributions to the fundamental understanding of luminescence processes at molecular level. The conclusions drawn from the dilute solution data, however, cannot commonly be extended to the concentrated solutions. Indeed, many Ir(III) complexes show very different light-emitting behaviors in dilute and concentrated solutions and respectively in the solid state. The luminescence is often weakened or quenched at high concentrations, a phenomenon widely known as “concentration quenching”. A main cause for the quenching process is mechanistically associated with the “formation of aggregates”, which is probably why the concentration quenching effect has frequently been referred to as “aggregationcaused quenching” (ACQ). On the other hand “aggregation-induced phosphorescent emission” (AIPE) is an unusual phenomenon existing also in transition metal complexes, which have no emission in solution but enhanced emission in the solid state.7 There are some examples of AIPE, most of them in neutral Ir(III) complexes.8, 9, 10, 11, 12 The main strategies to avoid unpleasant quenching phenomena are based on the dispersion of the chromophore. Mainly, two strategies are employed: engineering at molecular level by introducing functionalities able to electronically disconnect the chromophores (bulky groups or functionalities capable to construct hard crystalline or soft dynamic supramolecular assemblies) or isolating the active molecules in different host matrices (host-guest systems).13 In particular, the dispersion of a chromophore into mesoporous materials not only prevents the aggregation phenomena but also provides increased thermal, chemical and mechanical stability to the final materials. Mesoporous materials are ordered porous materials with periodic distribution of pores, high surface area, controllable large pore sizes in the range of 2 – 50 nm and variable topology of the pores. The inorganic matrixes may be made up of SiO2, TIO2, ZrO2, Al2O3, Nb2O5 etc. Basically, the synthesis of ordered functional mesoporous materials is based on the condensation of an inorganic scaffold on the organised structure formed in water by surfactant molecules. Two different strategies may be employed, the cooperative self-assembly mechanism (CSA) and the true liquid crystal templating’ (TLCT) mechanism.14 The functionalization of the mesoporous material may be done in both cases by inserting the chromophore into the primarily water solution. Therefore, water soluble chromophores may guarantee a better compatibility with the surfactant/water system, whereas a proper functionalization on the molecular structure of the chromophore that permit the self-assembly into supramolecular ordered water assemblies, will allow to use the chromophores directly as structure directing agents (SDAs). Since the photophysical properties of the ionic complexes are influenced profoundly by the surroundings of the molecule both in solution and in condensed states, it is fundamental to study the behavior of such complexes in these different states, in order to achieve a fine tuning of the properties as a function of their structure and order in the final material. The knowledge gained in the assembling of supramolecular materials using non-covalent bonds may be used for the construction of ordered systems in water. This strategy will permit the one-step synthesis of functional mesoporous materials, and to control the order of the final material controlling the order in water of the functional Ir(III) complexes. In particular, the molecular fragments that one can change to achieve the desired properties in the final ionic Ir(III) complexes are the cyclometallating or coordinating ligands, and respectively the counterion. My research therefore is focused on the design and synthesis of hydrophilic ionic Ir(III) complexes with flexible or rigid ancillary ligands and use of different counterions, all suitable for controlling the supramolecular assembly in the solid state, and to transfer the knowledge gained into obtaining ordered structures in water, or water-surfactant systems, necessary for the synthesis of mesoporous materials with defined properties. The ionic octahedral Ir(III) complexes synthesised during this thesis and their classification in different classes are presented in the figure S1Università della Calabri