Contents Chapter 1 Introduction 1 Chapter 2 Concepts on Electron Transfer Theory 5 2.1 General kinetic context of the excited-state quenching dynamics by electron transfer reaction 5 2.2 Short description on Born-Oppenheimer approximation 8 2.3 Electron transfer rate expression within Born-Oppenheimer approximation 10 2.4 Fermi's Golden Rule and its application in electronic transition 12 2.5 Frank-Condon principle applied to Marcus correction for electron transfer rate 13 2.6 Vibrational resolved electron transfer rate 18 Chapter 3 Energetic Driving Force for Electron Transfer Reaction 24 3.1 Free energy changes in primary electron transfer 24 3.2 Coulombic attraction energy corrected free energy changes 26 3.3 Development of free energy changes in external environment 28 Chapter 4 Electronic Barriers for Electron Transfer Reaction 38 4.1 Two-state model 39 4.2 Calculating protocols for electron transfer integral 40 4.2.1 Energy-gap-based approaches 41 4.2.2 Direct calculation of the o-diagonal matrix elements 44 4.2.3 The generalized Mulliken-Hush scheme and its variants 46 4.3 The development of generalized Mulliken-Hush method 50 4.4 Nuclear Barriers for Electron Transfer Reaction 56 4.5 Nuclear barriers from bond length change 58 4.6 Nuclear barriers from solvent reorganization 61 4.7 Estimation of reorganization energy from vibronic transition spectra 65 4.8 The external electric-eld controlled reorganization energy 66 Chapter 5 Experimental Measurement and Theoretical Simulation on Electron Transfer Reaction Rate in Organic Solar Cell Materials 73 5.1 Key role of electron transfer reaction rate in organic solar cell materials 73 5.2 Brief introduction on polymer-fullerene bulk heterojunction solar cell 77 5.3 Relevant experimental measurement on electron transfer reaction rate 81 5.4 Theoretical simulation on electron transfer reaction rate 96 5.4.1 Electron transfer rate simulation by employing Marcus theory 96 5.4.2 Electron transfer rate simulation by employing Marcus-Levich-Jortner's formalism 100 Chapter 6 The Visualized Method Direct Visual Evidence for Electron Transfer 104 Chapter 7 Perspective 113 References 115