The article discusses the molecular exciton model in molecular spectroscopy, focusing on how electronic transitions in molecular aggregates and composite systems influence spectral properties. It traces the historical development of the model, starting from early experiments by Kautsky and Merkel, who observed that molecular aggregation could enhance metastable state excitation, and later contributions by Förster and Lewis and Kasha. The model is used to explain the splitting of excited states in dimers, trimers, and larger molecular aggregates, leading to observable spectral shifts and enhanced triplet state excitation. The theoretical framework of the exciton model is presented, including the derivation of energy levels for molecular dimers and the role of intermolecular interactions. The model is shown to describe the splitting of excited states in aggregates, with the ground state being slightly affected by van der Waals interactions. The model also explains the enhancement of triplet state excitation, which can occur even in cases where no significant exciton effect is observed in the singlet-singlet absorption spectrum. The article includes detailed energy diagrams for various composite systems, such as parallel, in-line, and oblique transition dipoles, illustrating how the orientation and geometry of molecules influence exciton splitting and transition probabilities. It also discusses the effects of different molecular configurations on the phosphorescence and fluorescence properties of composite molecules, showing that even small changes in molecular structure can lead to significant enhancements in triplet state excitation. The study presents experimental examples of triplet state excitation enhancement in covalently bonded composite molecules, such as aryl methanes and aryl amines, demonstrating that even in cases of weak or intermediate coupling, the exciton model can predict and explain the observed phenomena. The results show that the phosphorescence-to-fluorescence ratio increases in these systems, indicating a significant enhancement of triplet state excitation. The article concludes that the exciton model provides a necessary explanation for these phenomena, particularly in the context of molecular aggregates and composite systems.The article discusses the molecular exciton model in molecular spectroscopy, focusing on how electronic transitions in molecular aggregates and composite systems influence spectral properties. It traces the historical development of the model, starting from early experiments by Kautsky and Merkel, who observed that molecular aggregation could enhance metastable state excitation, and later contributions by Förster and Lewis and Kasha. The model is used to explain the splitting of excited states in dimers, trimers, and larger molecular aggregates, leading to observable spectral shifts and enhanced triplet state excitation. The theoretical framework of the exciton model is presented, including the derivation of energy levels for molecular dimers and the role of intermolecular interactions. The model is shown to describe the splitting of excited states in aggregates, with the ground state being slightly affected by van der Waals interactions. The model also explains the enhancement of triplet state excitation, which can occur even in cases where no significant exciton effect is observed in the singlet-singlet absorption spectrum. The article includes detailed energy diagrams for various composite systems, such as parallel, in-line, and oblique transition dipoles, illustrating how the orientation and geometry of molecules influence exciton splitting and transition probabilities. It also discusses the effects of different molecular configurations on the phosphorescence and fluorescence properties of composite molecules, showing that even small changes in molecular structure can lead to significant enhancements in triplet state excitation. The study presents experimental examples of triplet state excitation enhancement in covalently bonded composite molecules, such as aryl methanes and aryl amines, demonstrating that even in cases of weak or intermediate coupling, the exciton model can predict and explain the observed phenomena. The results show that the phosphorescence-to-fluorescence ratio increases in these systems, indicating a significant enhancement of triplet state excitation. The article concludes that the exciton model provides a necessary explanation for these phenomena, particularly in the context of molecular aggregates and composite systems.