The molecular exciton model is a theoretical framework used to describe the interaction of excited states in molecular aggregates and composite molecules. It has been extensively applied to molecular crystals and more recently to non-crystalline systems such as van der Waals and hydrogen-bonded dimers, trimers, and higher-order aggregates. The model explains how electronic transitions in component sub-units can lead to exciton splitting, resulting in spectral shifts or splittings of absorption bands. This effect can also enhance triplet state excitation, even when no significant exciton effect is observable in singlet-singlet absorption spectra. The model is based on the interaction of transition dipoles and considers the energy levels of excited states in composite molecules. The exciton splitting energy depends on the square of the transition moment and the inverse cube of the intermolecular distance. The model has been applied to various composite systems, including molecular dimers, trimers, and triple molecules, with different geometrical arrangements of transition dipoles. The results show that the exciton model can explain the observed spectral and luminescence properties of these systems, including the enhancement of triplet state excitation and the quenching of fluorescence. The model has been supported by experimental studies on molecules such as diphenylmethane, triphenylmethane, and aromatic amines. These studies demonstrate that even in cases of weak or intermediate coupling, triplet state excitation can be significantly enhanced. The results also show that the phosphorescence quantum yield increases, while the phosphorescence lifetime remains relatively constant. This suggests that the exciton model provides a necessary explanation for the observed phenomena in composite molecules. The molecular exciton model is a valuable tool for understanding the photochemical and spectroscopic properties of composite molecules. It has been applied to various systems, including aromatic hydrocarbons and amines, and has provided insights into the mechanisms of triplet state excitation and luminescence. The model's predictions have been confirmed by experimental data, and it has been shown to be particularly useful in detecting weak interactions in molecular composite systems. The model also has important implications for the design of photochemical systems, as it suggests that triplet state excitation can be significantly enhanced by constructing composite molecules with specific geometrical arrangements.The molecular exciton model is a theoretical framework used to describe the interaction of excited states in molecular aggregates and composite molecules. It has been extensively applied to molecular crystals and more recently to non-crystalline systems such as van der Waals and hydrogen-bonded dimers, trimers, and higher-order aggregates. The model explains how electronic transitions in component sub-units can lead to exciton splitting, resulting in spectral shifts or splittings of absorption bands. This effect can also enhance triplet state excitation, even when no significant exciton effect is observable in singlet-singlet absorption spectra. The model is based on the interaction of transition dipoles and considers the energy levels of excited states in composite molecules. The exciton splitting energy depends on the square of the transition moment and the inverse cube of the intermolecular distance. The model has been applied to various composite systems, including molecular dimers, trimers, and triple molecules, with different geometrical arrangements of transition dipoles. The results show that the exciton model can explain the observed spectral and luminescence properties of these systems, including the enhancement of triplet state excitation and the quenching of fluorescence. The model has been supported by experimental studies on molecules such as diphenylmethane, triphenylmethane, and aromatic amines. These studies demonstrate that even in cases of weak or intermediate coupling, triplet state excitation can be significantly enhanced. The results also show that the phosphorescence quantum yield increases, while the phosphorescence lifetime remains relatively constant. This suggests that the exciton model provides a necessary explanation for the observed phenomena in composite molecules. The molecular exciton model is a valuable tool for understanding the photochemical and spectroscopic properties of composite molecules. It has been applied to various systems, including aromatic hydrocarbons and amines, and has provided insights into the mechanisms of triplet state excitation and luminescence. The model's predictions have been confirmed by experimental data, and it has been shown to be particularly useful in detecting weak interactions in molecular composite systems. The model also has important implications for the design of photochemical systems, as it suggests that triplet state excitation can be significantly enhanced by constructing composite molecules with specific geometrical arrangements.