Organic Molecular Crystals: Their Electronic States

1. Introduction: Characteristic Features of Organic Molecular Crystals. - 1.1 Interaction Forces in Molecular Crystals. - 1.2 The Atom-Atom Potential Method. - 1.3 Aromatic Hydrocarbons - Model Compounds of Organic Molecular Crystals. - 1.3.1 Anthracene. - Anthracene as Model Compound. - Molecular Structure. - Basic Molecular Parameters. - Crystal Structure. - Elastic and Optical Properties. - Metastable Phases in Anthracene. - 1.3.2 Naphthalene. - Molecular Structure. - Basic Molecular Parameters. - Crystal Structure. - Elastic and Optical Properties. - 1.3.3 Higher Linear Polyacenes. - Tetracene and Pentacene. - Hexacene. - 1.3.4 Other Model Aromatic Compounds. - 1.4 Specific Properties of Electronic States in a Molecular Crystal. - 1.5 Basic Characteristics of Electronic Conduction States in Molecular Crystals. - 1.5.1 Band Theory Approach. - 1.5.2 Hopping Versus Band Model. - 1.5.3 Band-to-Hopping Transition. - 1.5.4 Electronic Polarization and Charge Carrier Self-Energy. - 1.5.5 Other Types of Interaction. - 2. Electronic States of an Ideal Molecular Crystal. - 2.1 Neutral Excited States in a Molecular Crystal. - 2.2 Ionized States in a Molecular Crystal. - 2.2.1 The Lyons Model of Ionized States. - 2.2.2 A Modified Lyons Model. - 2.3 Electronic Polarization of a Molecular Crystal by a Charge Carrier. - 2.3.1 Some General Considerations. - 2.3.2 Dynamic and Microelectrostatic Approaches to Electronic Polarization in Molecular Crystals. - 2.4 Electrostatic Methods of Electronic Polarization Energy Calculation in Molecular Crystals. - 2.4.1 Microelectrostatic Methods of Zero-Order Approximation. - 2.4.2 Method of Self-Consistent Polarization Field. - 2.5 Determination of Molecular Polarizability Tensor. - 2.5.1 Experimental Methods. - 2.5.2 Theoretical Methods. - 2.6 Selection of Molecular Polarizability Components bi. for Electronic Polarization Energy Calculations. - 2.7 Extended Polarization Model of Ionized States in Molecular Crystal s. - 2.7. 1 Intrinsic Electronic Polarization of a Molecule by a Localized Charge Carrier. - 2.7. 2 Vibronic Relaxation and Ionic State Formation. - 2.7. 3 Extended Polarization Model Including Ionic States of Electronic Conductivity. - 2.7. 4 Dynamic Electronic Polaron States in a Molecular Crystal. - 2.8 Charge Transfer (CT) States in Molecular Crystals. - 2.8. 1 General on CT States. - 2.8. 2 Evaluation of CT-State Energies in Anthracene and Naphthalene Crystals. - 2.8. 3 CT States in Photogeneration Processes. - 2.8. 4 CT States in Recombination Processes. - 2.9 Experimental Determination of Energy Structure Parameters in Molecular Crystals. - 2.10 Energy Structure of an Anthracene Crystal. - 2.11 Energy Structure of Aromatic and Heterocyclic Molecular Crystals. - 3. Role of Structural Defects in the Formation of Local Electronic States in Molecular Crystals. - 3.1 Statistical Aspects of the Formation of Local States of Polarization Origin. - 3.2 General Considerations on the Role of Specific Structural Defects. - 3.3 Point Defects (Vacancies) in Molecular Crystals, Their Crystallographic and Electronic Properties. - 3.4 Dislocation Defects, Their Role in Local State Formation. - 3.5 Energetics of Dislocations in Molecular Crystals. - 3.5.1 Discrete Configuration of Dislocations. - 3.5.2 Basic Elastic Properties of Anthracene and Naphthalene Crystals. - 3.5.3 Energy Estimates for Basal Edge Dislocations in an Anthracene Crystal. - 3.6 Atomic and Molecular Models of the Dislocation Core. - 3.6. 1 Models of Spherical Atoms and Molecules. - 3.6. 2 Polyatomic Molecular Models. - 3.7 Dislocation Alignments and Aggregations, Their Configurational and Energetic Properties. - 3.7. 1 Interaction Between Dislocations. - 3.7. 2 Dislocation Alignments. - 3.7. 3 Dislocation Ensembles. - 3.8 Grain Boundaries, Their Energetic Characteristics. - 3.8. 1 Energy of Grain Boundaries in Molecular Crystals. - 3.8. 2 Relative Lattice Compression on Grain Boundaries of an Anthracene Crystal. - 3.9 Stacking Faults in Molecular Crystals. - 3.9. 1 General on Stacking Faults. - 3.9. 2 Stacking Faults in Anthracene-Type Crystals, Their Energetic Characteristics. - 3.9. 3 Calculations of Equilibrium Configuration of Molecules in Stacking Faults of an Anthracene Crystal. - 3.10 Formation of Predimer States in the Regions of Extended Structural Defects of Anthracene-Type Crystals. - 3.11 Some More Complex Two- and Three-Dimensional Lattice Defects in Molecular Crystals. - 3.12 Observation of Structural Defects in Molecular Crystals. - 3.12.1 Optical Low Resolution Technique. - 3.12.2 Electron Microscopy and Diffraction Techniques. - 3.12.3 X-Ray Methods. - 3.13 Main Characteristics of Dislocation Defects in Some Model Molecular Crystals. - 3.13.1 Dominant Types of Dislocatioas in Anthracene Space Group Crystal s. - 3.13.2 Density of Dislocations in Anthracene Crystals, Its Dependence on Crystal Growth and Treatment. - 4. Local Trapping Centers for Excitons in Molecular Crystals. - 4.1 Theory of Exciton States in a Deformed Molecular Crystal. - 4.2 Electron Level Shifts in Hydrostatically Compressed Molecular Crystal s. - 4.3 Formation of Local Exciton Trapping Centers in Structural Defects of a Crystal. - 5. Local Trapping States for Charge Carriers in Molecular Crystals. - 5.1 Electronic Polarization Energy of a Compressed Anthracene Crystal. - 5.2 Formation of Local Trapping Centers for Charge Carriers in Structural Defects of a Real Molecular Crystal. - 5.3 Energy Spectrum of Local States of Polarization Origin in Stacking Faults of an Anthracene Crystal. - 5.4 Local Surface States of Polarization Origin in Molecular Crystals. - 5.5 Local States of Polarization Origin in the Vicinity of a Lattice Vacancy. - 5.6 Local Charge Carrier Trapping in Covalent, Ionic and Molecular Crystal s. - 5.7 Randomizing Factors Determining Gaussian Distribution of Local States of Structural Origin. - 5.8 Investigation of Local Trapping States by Method of Space Charge Limited Currents (SCLC). - 5.8. 1 General Considerations. - 5.8. 2 Injecting and Blocking Contacts. - 5.8. 3 Conventional SCLC Theories of Discrete and Exponential Approximation of Trap Distribution. - SCLC Theory for an Insulator With Discrete Trap Distribution. - SCLC Theory for an Insulator With Exponential Trap Distribution. - Applicability Limits of Diffusion-Free SCLC Theory Approximation. - 5.8. 4 Criteria for Validity of SCLC Conditions. - 5.8. 5 Difficulties in Interpreting Experimental CV Characteristics in Terms of Discrete and Exponential Trap Distribution Models. - 5.9 Phenomenological SCLC Theory for Molecular Crystals with Gaussian Distribution of Local Trapping States. - 5.9. 1 Conceptual Basis. - 5.9. 2 Basic SCLC Theory Equations. - 5.9. 3 Validity Range for Different Analytical SCLC Approximations. - 5.9. 4 SCLC Dependence on Dispersion Parameter a. - 5.9. 5 SCLC Temperature Dependences for Ge (E) and Gg (E) Distributions. - 5.9. 6 SCLC Dependence on Et Value. - 5.9. 7 Validity Criteria for Exponential and Gaussian Approximations. - 5.9. 8 CV Characteristics for Two Sets of Gaussian Trap Distribution. - 5.10 Gaussian SCLC Approximations of Experimental CV Characteristics. - 5.10. 1 Analytical Approximations. - 5.10. 2 Differential Method of Analysis of CV Characteristics. - 5.11 SCLC Theory for Spatially Nonuniform Trap Distribution. - 5.12 Investigation of Local Trapping States by Thermally Activated Spectroscopy Techniques. - 5.13 Other Experimental Methods for Local Trapping State Study. - 5.14 Correlations Between Distribution Parameters of Local Trapping States and Crystalline Structure. - 5.15 Local Lattice Polarization by Trapped Charge Carrier in Molecular Crystals. - 5.16 Guest Molecules as Trapping Centers in a Host Lattice. - 6. Summing Up and Looking Ahead. - References. - Additional References with Titles.