INFLUENCE OF SUBSTRATE ON PHYSICAL PROPERTIES OF TRANSITION METAL COMPLEXES THIN FILMS

In order to exploit the potential of transition metal complexes in novel optoelectronic devices, it is crucial to gain thorough understanding of their interfacial electronic properties with conducting substrates and establish interconnection between structural and physical properties of transition metal complexes thin films on technologically important substrates. The thesis aims to establish the interconnection between structural and physical properties of tetrapyrrole complexes by underscoring the significance of intermolecular interactions, structural deformations and molecular order, providing useful insights for the creation and control of functional molecular films, crucial for the technological applications of organic semiconductors. A multi-technique characterization approach has been adopted approach based on electronic and absorption spectroscopies and structural diffraction techniques. Inverse photoemission spectroscopy has been utilized to highlight the influence of intermolecular interactions on unoccupied density of states as empty orbitals are more sensitive to the intermolecular interaction due to their higher delocalization around the macrocycle. Photoemission and X-ray absorption spectroscopy have been utilized to demonstrate the ability of graphene to control the interaction of FeTPP-Cl adsorbed onto Gr/Ni(111) and Gr/Pt(111) substrates. It has been demonstrated that interfacial charge transfer can be significantly influenced by the introduction of graphene buffer layer between transition metal complexes adsorbed on metallic substrates. Inverse photoemission spectroscopy has been utilized for metal phthalocyanine and metal octaethylporphyrin thin films on metallic substrates to investigate the subtle changes induced by central metal atom, intermolecular interactions and peripheral ethyl groups on unoccupied density of states. FePc and CoPc thin films deposited on technologically important substrates such as SiOx/Si , ITO and Au reveals that the vibrational properties have strong dependence on molecular stacking adopted by molecules which in turn depends on substrate roughness, intermolecular interactions and molecule-substrate interactions. We have employed vacuum deposited Zinc Octaethyl porphyrin (ZnOEP) thin films with a different degree of long-range order as model systems An asymmetrical stretching of skeletal carbon atoms of the porphyrin conformer has been observed and attributed to the ordered molecular stacking and intermolecular interactions. X-ray absorption near edge structure (XANES) establishes a symmetry reduction in the molecular conformer involving skeletal carbon atoms of the porphyrin ring for the ordered films highlighting the consequences of increased pi stacking of ZnOEP molecules adopting triclinic structure. The observed asymmetrical stretching of pi conjugation network of porphyrin structure can have significant implications on the charge transport and light harvesting ability of porphyrin thin films on substrates.

In order to exploit the potential of transition metal complexes in novel optoelectronic devices, it is crucial to gain a thorough understanding of their interfacial electronic properties with conducting substrates and establish interconnection between structural and physical properties of transition metal complexes thin films on technologically important substrates. The thesis aims to establish the interconnection between structural and physical properties of tetrapyrrole complexes by underscoring the significance of intermolecular interactions, structural deformations, and molecular order, providing useful insights for the creation and control of functional molecular films, crucial for the technological applications of organic semiconductors. A multi-technique characterization approach has been adopted approach based on electronic and absorption spectroscopies and structural diffraction techniques. Inverse photoemission spectroscopy has been utilized to highlight the influence of intermolecular interactions on unoccupied density of states as empty orbitals are more sensitive to the intermolecular interaction due to their higher delocalization around the macrocycle. Photoemission and X-ray absorption spectroscopy have been utilized to demonstrate the ability of graphene to control the interaction of FeTPP-Cl adsorbed onto Gr/Ni(111) and Gr/Pt(111) substrates. It has been demonstrated that interfacial charge transfer can be significantly influenced by the introduction of graphene buffer layer between transition metal complexes adsorbed on metallic substrates. Inverse photoemission spectroscopy has been utilized for metal phthalocyanine and metal octaethylporphyrin thin films on metallic substrates to investigate the subtle changes induced by central metal atom, intermolecular interactions and peripheral ethyl groups on unoccupied density of states. FePc and CoPc thin films deposited on technologically important substrates such as SiOx/Si , ITO and Au reveals that the vibrational properties have strong dependence on molecular stacking adopted by molecules which in turn depends on substrate roughness, intermolecular interactions and molecule-substrate interactions. We have employed vacuum deposited Zinc Octaethyl porphyrin (ZnOEP) thin films with a different degree of long-range order as model systems An asymmetrical stretching of skeletal carbon atoms of the porphyrin conformer has been observed and attributed to the ordered molecular stacking and intermolecular interactions. X-ray absorption near edge structure (XANES) establishes a symmetry reduction in the molecular conformer involving skeletal carbon atoms of the porphyrin ring for the ordered films highlighting the consequences of increased pi stacking of ZnOEP molecules adopting triclinic structure. The observed asymmetrical stretching of pi conjugation network of porphyrin structure can have significant implications on the charge transport and light harvesting ability of porphyrin thin films on substrates.