DFT/TD-DFT, optical and electrochemical studies of transition metal alkynyl complexes for nonlinear optics

Abstract

The design of new organometallic complexes with large nonlinear optical (NLO) properties is currently the subject of extensive investigations by theoretical and experimental methods, since they have potential applications in technologies like optical signal processing, switching, frequency generation, optical data storage, optical communication, and image processing. This thesis aims at (1) rationalizing the experimental observations of ruthenium and osmium alkynyl complexes and (2) designing novel metal alkynyl complexes and analyzing their properties with time-dependent density functional (TD-DFT) theoretical studies. Chapter 1 presents an introduction to nonlinear optics, mathematical representations of NLO phenomena, experimental techniques for measuring NLO properties and a review of organometallic complexes that have had their NLO properties measured. Chapter 2 discusses the evolution of computational chemistry theories from fundamental ab initio and semi-empirical methods to recently developed TD-DFT theories. Chapter 3 reports benchmarking of TD-DFT studies on linear and NLO properties of ruthenium and osmium alkynyl complexes. The experimental linear and NLO properties have been reported and benchmark calculations have been carried out to analyze the ability of TD-DFT methods to reproduce the experimental observations consistently. Chapter 4 rationalizes the experimentally observed structural and linear optical properties for ruthenium and osmium alkynyl complexes with different donor acceptor ligand combinations via DFT/TD-DFT calculations. Chapter 5 reports TD-DFT calculations of the linear and NLO properties of alkynylruthenium complexes with extended bridges. Four types of bridges are studied; (1) phenyleneethynylene, (2) phenylenevinylene, (3) phenyleneimino, and (4) phenyleneazo. For each alkynylruthenium series the analogous organic series was analyzed. Chapter 6 employs TD-DFT calculations to rationalize the linear and NLO properties of homometallic and heterobimetallic alkynyl complexes with ruthenium and osmium metal centres and different donor acceptor ligand combinations. Cyclic voltammetry and spectroelectrochemistry experiments were carried out for ruthenium homometallic complexes. Chapter 7 extends the TD-DFT calculations performed on 1D linear complexes (Chapters 3-6) to 2D V-shaped homobimetallic ruthenium alkynyl complexes with different donor acceptor ligand combinations. The experimental linear and NLO properties were rationalized with calculations. Chapter 8 reports linear optical properties on core geometry variation by changing the ruthenium alkynyl substitution pattern of the phenyl core. The experimental structures with large numbers of atoms were simplified incorporating ligand simplification methods analyzed in Chapter 3. The linear optical data for experimentally synthesized complexes are rationalized with TD-DFT calculations and trends were predicted for complexes that have not yet been synthesized in the series. Chapter 9 presents an experimental and TD-DFT analysis for linear and related star-shaped ruthenium alkynyl complexes. The charge transfer involved in linear and 1,3,5-substituted octupolar complexes are analyze with experimental and TD-DFT UV-Vis spectra. Novel linear and star shaped complexes were analyzed with calculated structures where the experimental structures are not reported due to difficulties in synthesis. Show more