I. Introduction 237
II. Electron Paramagnetic Resonance in Organic Semiconductors 238
1. EPR Observation of Triplet States of Organic Crystals 238
2. Triplet Excitons in Charge-transfer Complexes and Other Organic Semiconductors 240
3. Activation Energy of Singlet-triplet Transitions and Width of the Forbidden Band 245
III. Nuclear Quadrupole and Nuclear Magnetic Resonance of Organic Semiconductors 247
1. Study of the Nature of Chemical Bonds in Charge-transfer Complexes 247
2. Temperature Dependence of Frequencies 249
3. Temperature Dependence of Relaxation Times 251
IV. Conclusion 252
Bibliography 253