archives@tulane.edu / 1 / Malathy Pratheepkumar

Square planar metal bis-dithiolenes are interesting targets for incorporation into electronic and optoelectronic devices as they characteristically display multiple stable redox states, coupled with strong absorption at particularly low energies. This work focuses on novel methods for the formation of thin films of metal bis-dithiolenes for incorporation into devices. The synthesis, structure and spectroscopic properties of a novel class of polymerisable heteroleptic nickel dithiolene complex, containing pendent thiophene units, [Ni(R2pipdt)(b-3ted)] are described [R = Bz (3a), iPr (3b); pipdt = piperazine- 3,2-dithione; b-3ted = bis-(3-thienyl)-1,2-ethylenedithiolene]. Electrooxidation of (3a) showed it to incorporate into a polymeric film over an electrode surface, which consisted of intact dithiolene units, by covalent linking of the pendent thienyl groups. This polymer film showed some redox activity, with the intense, low energy, absorption red-shifted by 4360 cm-1. Co-polymerisation of (3a) with thiophene yielded a highly conductive film, with the intense, low energy, absorption red-shifted to a lesser extent (3500 cm-1). The films displayed interesting optical properties, however, their use was restricted by their poor redox activity, thought to be due to poor ion transport through the films. The synthesis of two novel dithiolene ligand systems, containing pendent polymerisable indolyl groups (mi-5edt and mi-5hdt), are described, and their incorporation into complexes investigated for nickel [Ni(mi-5edt)2 (6) and Ni(mi-5hdt)2 (8)], and copper f[Cu(mi-5edt)2][TMA] ([7][TMA]) and [Cu(mi-5hdt)2][TMA] ([9][TMA])g investigated [(mi-5edt) = 1-(N-methylindol-5-yl)-ethane-1,2-dithiolate and (mi-5hdt) = 1- (N-methylindol-5-yl)-hex-1-ene-1,2-dithiolate, TMA = tetramethylammonium]. Each complex was characterised in terms of its structure, redox and optical properties, and the effect of the ligand design, and the metal centre, compared. The complexes of nickel were shown to yield polymer films under electrooxidative conditions, through covalent linking of the indolyl groups, with superior redox activity to 3a, and with an equally intense low energy absorption. The monoanionic complexes of copper were shown to deposit, under electrooxidative conditions, as neutral molecular films that were otherwise unobtainable by conventional solution techniques. The incorporation of the more soluble novel indolyl functionalised nickel dithiolene 8 into electronic devices was investigated. Electrochromic devices were formed using poly- 8 as the active layer. The devices were able to switch their optical absorption profile at 860 nm through three absorbing states by application of a suitable potential difference across the film. Field-effect transistors were fabricated using a molecular film of 8 as the active layer. The devices showed ambipolar charge transport properties, though with a bias for n-channel operation, with mobilities μ ≈ 1 x 10-4 cm2V-1s-1. Photovoltaic devices were formed from a blended film of 8 with P-3HT and with MDMO-PPV [P-3HT = regioregular poly-3-hexylthiophene, MDMO-PPV = poly(2-methoxy-5- (3',7'-dimethyloctyloxy)-1,4-phenylene-vynylene)]. 8 was shown to contribute to the photocurrent at wavelengths beyond the polymer component, thus harvesting more visible light, however efficiencies below 0.1 % suggested inefficient charge transport by 8 in the film. Structurally continuous films of Ni(b-3ted)2 (10) could be formed by a process of electrodeposition. The formed films displayed conductivities 40 times greater than for conventional solution cast films. By a detailed study of the level of residual ion doping, the molecular packing, and the morphology of the films, this improved performance was attributed to the formation of a more dense polycrystalline array, with larger crystallites, which formed good electronic contact with the electrodes, and with each other. This electrodeposition technique was used to fabricate field-effect transistors from 10. The devices showed poor mobilities (μ ≈ 1 x 10 -8 cm2V-1s-1), owing to the poor intermolecular overlap of the dithiolene units in the solid-state, but suggested this technique to be suitable for a wide range of semiconductors, with more favourable electronic properties, as an alternative to conventional vapour or solution deposition.

Asymmetric catalysis is one of the most effective ways to control a target molecule’s stereochemistry. Through the development of a wide variety of chiral transition metal complexes, synthetic chemists are given the tools they need to synthesize the desired enantiomer of numerous compounds. This work focuses on exploiting the non-innocent ligand reactivity of metal bis-dithiolenes with multiple conjugated π systems in order to synthesize chiral ligands. Recent work has shown that platinum bis-dithiolene reacts with dienes stereoselectively to form a racemic mix of C2 -chiral thioether ligands. The present contribution will show approaches to synthesizing chiral dienes and organometallic complexes with potential applications for asymmetric allylic substitution reactions. Dienes with various chiral auxiliaries were reacted with platinum dithiolene and monitored through NMR spectroscopy. Attempts to synthesis palladium bis-dithiolene complexes, not previously seen in the literature were made, and the reaction of α-β unsaturated ketones with metal bis-dithiolenes was explored.

Asymmetric catalysis is one of the most effective ways to control a target molecule’s stereochemistry. Through the development of a wide variety of chiral transition metal complexes, synthetic chemists are given the tools they need to synthesize the desired enantiomer of numerous compounds. This work focuses on exploiting the non-innocent ligand reactivity of metal bis-dithiolenes with multiple conjugated π systems in order to synthesize chiral ligands. Recent work has shown that platinum bis-dithiolene reacts with dienes stereoselectively to form a racemic mix of C2 -chiral thioether ligands. The present contribution will show approaches to synthesizing chiral dienes and organometallic complexes with potential applications for asymmetric allylic substitution reactions. Dienes with various chiral auxiliaries were reacted with platinum dithiolene and monitored through NMR spectroscopy. Attempts to synthesis palladium bis-dithiolene complexes, not previously seen in the literature were made, and the reaction of α-β unsaturated ketones with metal bis-dithiolenes was explored.

Σκοπός της παρούσας διδακτορικής διατριβής ήταν ο προσδιορισμός της υπερπολωσιμότητας δεύτερης τάξης διάφορων φουλλερενίων, παραγώγων φουλλερενίων και διθειολενικών συμπλόκων και η συσχέτιση αυτής με τη χημική δομή των υπό μελέτη υλικών. Για τη μελέτη των μη-γραμμικών οπτικών ιδιοτήτων των υλικών αυτών χρησιμοποιήθηκε η τεχνική Z-scan. Η μη-γραμμική τους απόκριση μελετήθηκε για παλμική διέγερση 35 ps και 8 ns, στα 532 και 1064 nm. Παράγοντες όπως ενίσχυση λόγω συντονισμού, μείωση της συμμετρίας, απεντοπισμός ηλεκτρονίων και μεταφορά φορτίου βρέθηκαν ότι επηρεάζουν σημαντικά τις μη-γραμμικές οπτικές ιδιότητες των συστημάτων αυτών. / The objective of this thesis was the determination of the second-order hyperpolarizability of some fullerenes, fullerene derivatives and dithiolene complexes and the understanding of the relation between the hyperpolarizability and the molecular structure. The non-linear optical properties of the above systems were investigated by the Z-scan technique. In particular, their non-linear optical response was studied under pulsed laser excitation having duration 35 ps and 8 ns, at 532 and 1064 nm. Several factors, like resonant enhancement, symmetry reduction, electron delocalization and charge transfer, were found to influence significantly the non-linear optical properties of these molecules.