Rational Design of Metal-organic Electronic Devices: a Computational Perspective

Organic and organometallic electronic materials continue to attract considerable attention among researchers due to their cost effectiveness, high flexibility, low temperature processing conditions and the continuous emergence of new semiconducting materials with tailored electronic properties. In addition, organic semiconductors can be used in a variety of important technological devices such as solar cells, field-effect transistors (FETs), flash memory, radio frequency identification (RFID) tags, light emitting diodes (LEDs), etc. However, organic materials have thus far not achieved the reliability and carrier mobility obtainable with inorganic silicon-based devices. Hence, there is a need for finding alternative electronic materials other than organic semiconductors to overcome the problems of inferior stability and performance. In this dissertation, I research the development of new transition metal based electronic materials which due to the presence of metal-metal, metal-?, and ?-? interactions may give rise to superior electronic and chemical properties versus their organic counterparts. Specifically, I performed computational modeling studies on platinum based charge transfer complexes and d10 cyclo-[M(?-L)]3 trimers (M = Ag, Au and L = monoanionic bidentate bridging (C/N~C/N) ligand). The research done is aimed to guide experimental chemists to make rational choices of metals, ligands, substituents in synthesizing novel organometallic electronic materials. Furthermore, the calculations presented here propose novel ways to tune the geometric, electronic, spectroscopic, and conduction properties in semiconducting materials. In addition to novel material development, electronic device performance can be improved by making a judicious choice of device components. I have studied the interfaces of a p-type metal-organic semiconductor viz cyclo-[Au(µ-Pz)]3 trimer with metal electrodes at atomic and surface levels. This work was aimed to guide the device engineers to choose the appropriate metal electrodes considering the chemical interactions at the interface. Additionally, the calculations performed on the interfaces provided valuable insight into binding energies, charge redistribution, change in the energy levels, dipole formation, etc., which are important parameters to consider while fabricating an electronic device. The research described in this dissertation highlights the application of unique computational modeling methods at different levels of theory to guide the experimental chemists and device engineers toward a rational design of transition metal based electronic devices with low cost and high performance

Modeling the Deposition of Metal Atoms on a p-Type Organometallic Conductor: Implications for Stability and Electron Transfer

Article discussing modeling the deposition of metal atoms on a p-Type organometallic conductor and implications for stability and electron transfer

Structure, Properties, and Reactivity of Porphyrins on Surfaces and Nanostructures with Periodic DFT Calculations

Porphyrins are fascinating molecules with applications spanning various scientific fields. In this review we present the use of periodic density functional theory (PDFT) calculations to study the structure, electronic properties, and reactivity of porphyrins on ordered two dimensional surfaces and in the formation of nanostructures. The focus of the review is to describe the application of PDFT calculations for bridging the gaps in experimental studies on porphyrin nanostructures and self-assembly on 2D surfaces. A survey of different DFT functionals used to study the porphyrin-based system as well as their advantages and disadvantages in studying these systems is presented

Surface directed reversible imidazole ligation to nickel(ii) octaethylporphyrin at the solution/solid interface: a single molecule level study

Scanning tunneling microscopy (STM) is used to study for the first time the reversible binding of imidazole (Im) and nickel(ii) octaethylporphyrin (NiOEP) supported on highly oriented pyrolytic graphite (HOPG) at the phenyloctane/NiOEP/HOPG interface at 25 °C. The ligation of Im to the NiOEP receptor while not observed in fluid solution is readily realized at the solution/HOPG interface. The coordination process scales with increasing Im concentration and can be effectively modeled by the Langmuir isotherm. At room temperature it is determined that the standard free energy of adsorption is ΔGc = -15.8 kJ mol(-1) and the standard enthalpy of adsorption is estimated to be ΔHc ≈ -80 kJ mol(-1). The reactivity of imidazole toward NiOEP adsorbed on HOPG is attributed to charge donation from the graphite stabilizing the Im-Ni bond. This charge transfer pathway is supported by molecular and periodic modeling calculations which indicate that the Im ligand behaves as a π-acceptor. DFT calculations also show that the nickel ion in the Im-NiOEP/HOPG complex is in a singlet ground state. This is surprising since both our calculations and previous experimental studies find a triplet ground state for the five and six coordinated Im-nickel(ii) porphyrins in the gas-phase or in solution. Both the experimental and the theoretical findings provide information that is useful for better understanding of chemical sensing/recognition and catalytic processes that utilize metal-organic complexes adsorbed on surfaces where the reactivity of the metal is moderated by the substrate

Periodic and Molecular Modeling Study of Donor - Acceptor Interactions in (dbbpy)Pt(tdt) • TENF and [Pt(dbbpy)(tdt)]₂ • TENF

This article discusses a periodic and molecular modeling study. Supramolecular stacked materials (dbbpy)Pt(tdt)•TENF and [Pt(dbbpy)(tdt)]₂•TENF are built from (dbbpy)Pt(tdt) donors (D) with TENF acceptors (A) (TENF = 2,4,5,7-tetranitro-9-fluorenone; dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt = 3,4-toluenedithiolate)

Structure and Bonding of Palladium Oxos as Possible Intermediates in Metal–Carbon Oxy Insertion Reactions

Analysis of the electronic structure of PdO complexes is reported utilizing multiconfigurational self-consistent field (MCSCF) theory. Models include hard (N) and soft (Cl) donors to mimic proposed Pd oxo intermediates. Calculations argue against formulation of a Pd^IV oxo intermediate as posited in earlier experimental studies of Pd^II-mediated oxy insertion: i.e., a square-pyramidal complex with a basal oxo ligand. However, low-energy structures with other coordination geometries (trigonal bipyramidal) and isomerism (basal O) were identified. The supporting ligand plays a role in stabilization of the PdO bond as indicated by calculations on the PdOCl₂ fragment and LPdOCl₂ (L = model diimine ligand)

In Situ Imaging and Computational Modeling Reveal That Thiophene Complexation with Co(II)porphyrin/Graphite Is Highly Cooperative

Scanning tunneling microscopy (STM) was employed to quantitively investigate in situ binding of 3-phenyl thiophene (PhTh) to Co(II)octaethyl porphyrin (CoOEP) supported on highly ordered pyrolytic graphite (HOPG) in fluid solution. To our knowledge, this is the first single-molecule level study of a complexation reaction between a metalloporphyrin and a sulfur base at the solution/solid interface and one of the few examples of thiophene coordination with a d7 transition metal. Real-time imaging experiments revealed that PhTh binds reversibly to HOPG-supported CoOEP at room temperature. The coordination process increases with increasing PhTh concentration. The nearest-neighbor analysis of STM images indicates that the complexation reaction is cooperative. Because PhTh does not bind to CoOEP in solution, the STM results strongly suggest that the presence of HOPG is crucial to observe ligand binding and cooperativity in this system. Periodic plane-wave density functional theory (DFT) computations corroborate that PhTh has low binding affinity toward CoOEP in solution but predict that the ligand can adsorb to CoOEP/HOPG through coordination with S atoms or interact through noncovalent π–π bonding with the porphyrin chromophore. Three possible structures were considered, and DFT theory was used to calculate binding energies and free energies. In solution and on the HOPG surface both a π–π configuration and a η1(S) configuration have similar computed energies. The η1(S) structure shows the largest stabilization in going from the vapor to adsorbed on HOPG. We also show that statistical analysis of nearest neighbors is more sensitive to cooperative binding than is fitting with the Temkin or Langmuir isotherm. The implication is that isotherm fitting alone is insufficient for identifying cooperative binding on surfaces

Use of [SbF₆]⁻ to Isolate Cationic Copper and Silver Adducts with More than One Ethylene on the Metal Center

Article discussing the use of [SbF₆]⁻ to isolate cationic copper and silver adducts with more than one ethylene on the metal center