Design and synthesis of photoactive molecules based on metal dithiolenes

This work reports on the design, synthesis and characterization of some homoleptic and heteroleptic d8 metal (Ni, Pd, Pt) dithiolene complexes. Chapter 1 provides the background required to properly design metal dithiolenes exhibiting desired properties. Chapter 2 describes the synthesis & characterization of homoleptic radical monoanionic complexes showing multi-properties. Among these, a platinum complex prepared using a ligand containing a quinoxaline moiety connected through a dithieno bridge to the dithiolene core, shows unusual anti- Kasha solution proton dependent luminescence. The interaction of protons with these complexes is described with a view to understand their photo/electrocatalytic behaviour in aqueous acidic systems. Photocatalytic preliminary experiments on noble metal free homoleptic Ni-complex for hydrogen production from aqueous acidic solutions are described. Chapter 3 describes design, synthesis and characterization of chiral/achiral heteroleptic d8 metal dithiolene complexes, suitable as donor-metal-acceptor chromophores for 2nd order NLO applications. It describes how with the presence or absence of acid (protons) in solutions of complexes can afford two switchable chemical forms (having different electronic properties) which can possibly display contrast in their NLO response. It also describes, by inclusion of chirality in the acceptor ligand, a non-centrosymmetric arrangement of molecules in crystalline medium to preserve NLO response in the bulk. Moreover, the unusual proton dependent dual luminescent properties of some of these complexes are described. Lastly Chapter 4 contains conclusions, perspectives and appendices for this work

Design and synthesis of photoactive molecules based on metal dithiolenes

This work reports on the design, synthesis and characterization of some homoleptic and heteroleptic d8 metal (Ni, Pd, Pt) dithiolene complexes. Chapter 1 provides the background required to properly design metal dithiolenes exhibiting desired properties. Chapter 2 describes the synthesis & characterization of homoleptic radical monoanionic complexes showing multi-properties. Among these, a platinum complex prepared using a ligand containing a quinoxaline moiety connected through a dithieno bridge to the dithiolene core, shows unusual anti- Kasha solution proton dependent luminescence. The interaction of protons with these complexes is described with a view to understand their photo/electrocatalytic behaviour in aqueous acidic systems. Photocatalytic preliminary experiments on noble metal free homoleptic Ni-complex for hydrogen production from aqueous acidic solutions are described. Chapter 3 describes design, synthesis and characterization of chiral/achiral heteroleptic d8 metal dithiolene complexes, suitable as donor-metal-acceptor chromophores for 2nd order NLO applications. It describes how with the presence or absence of acid (protons) in solutions of complexes can afford two switchable chemical forms (having different electronic properties) which can possibly display contrast in their NLO response. It also describes, by inclusion of chirality in the acceptor ligand, a non-centrosymmetric arrangement of molecules in crystalline medium to preserve NLO response in the bulk. Moreover, the unusual proton dependent dual luminescent properties of some of these complexes are described. Lastly Chapter 4 contains conclusions, perspectives and appendices for this work

Structural changes in MII dithione/dithiolato complexes (M = Ni, Pd, Pt) on varying the dithione functionalization

The Ni triad [M(R2pipdt)(dmit)] based on donor/acceptor S,S′ ligands, where R2pipdt = 1,4-diisopropyl-piperazine-2,3-dithione (acceptor) and dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato (donor), was completed by preparing and characterizing the Pd(2) and Pt(3) compounds in addition to the already known Ni(1) complex. The rationale behind the work was to compare the properties and structures inside the triad with those of the corresponding Ni(4), Pd(5) and Pt(6) complexes where R = Bz. Minor changes in the properties as redox active nonlinear second-order (NLO) chromophores were observed in solution for the two triads. Instead, different structural features, reflected by changes in the diffuse reflectance spectra, were observed in their crystals on changing R from Bz to Pri in the piperazine ring and also, more surprisingly, inside the triads. 2 (isostructural with 1) and 3 crystallized in monoclinic P21/n and orthorhombic Pbca space groups, respectively. The crystal packings of 2 and 3 are also markedly different. In particular 1 and 2 form head-to-tail dimers whereas 3 forms supramolecular layers characterized by a partial stack between the molecular planes. Large differences in the crystal structures, induced by the diverse number and types of interactions exchanged by the peripheral fragments of the ligands, were found in the Bz-triad. Indeed, the molecules are stacked in a head-to-head and in a head-to-tail fashion in 4 and in 5/6, respectively. Moreover, significantly different packings were observed. The Hirshfeld surface analysis was used to provide a detailed description of the main types of interactions involved in the crystal packing of the six complexes

Molecular engineering of heteroleptic metal-dithiolene complexes with optimized second-order NLO response

The structure-property relationship for the class of square-planar d 8 metal heteroleptic dithiolene complexes, which exhibit negative solvatochromism and high molecular first hyperpolarizability, is discussed on the basis of experimental and theoretical results. The role of each ligand and of the metal in the electronic distribution, is highlighted with the view to design candidates for optimal 2nd NLO response. This class of complexes, bearing groups with different electron-withdrawing capability attached to the dithiolene core, behaves as intervalence compounds where ligands occur in formally different oxidation states, one reducing (dithiolate, prevailing contribution to the highest occupied molecular orbital (HOMO) at high energy, the donor) and the other oxidizing (dithione, prevailing contribution to the lowest unoccupied molecular orbital (LUMO) at low energy, the acceptor). The HOMO-LUMO transition, mediated by the d orbitals of coordinated metal, has thus ligand to ligand or mixed metal-ligand to ligand charge transfer character and is responsible for the 2nd order NLO activity.Joint experimental and theoretical results highlight the factors affecting the high negative second-order polarizability values, which are relatable to the high difference in dipole moments between excited and ground state enhanced by the electric field of the solvent, the large oscillator strength for the charge transfer transition, and the relatively low energy gap. Moreover, in this geometrically defined donor-metal-acceptor arrangement, steric factors affect the electronic distribution and thus the NLO properties. Therefore, torsion angle at the dithione ligand inversely correlates with the oscillator strength and the molecular first hyperpolarizability.The properties of a polymethylmetacrylate film incorporating a sample belonging to this class of complexes and showing a good second-harmonic generation, are also discussed to support the potential for applications in optoelectronics of this class of 2nd order NLO-chromophores