Formation of excited-state charge- and electron-transfer complexes (exciplexes) is strongly influenced by steric factors. However, the transient nature of exciplexes has made it difficult to quantify the steric requirements because of competing electronic factors. To probe some of these aspects, fluorescence from three electronically related aromatic molecules—pyrene, 1,3,6,8-tetraphenylpyrene (TPPy), and 1,3,6,8-tetrakis(4-methoxy-2,6-dimethylphenyl)pyrene (PyOMe), which differ in accessibility to the pyrenyl core, has been quenched by a structurally diverse set of tertiary aliphatic amines and N,N-dialkylanilines. Correlations have been made among the quenching rate constants in terms of both steric factors and electronic properties (e.g., sizes, shapes, conformational labilities, excitation energies, and oxidation or reduction potentials). It is found that quenching by tertiary amines is influenced by intermolecular distance and the angle between the lone pair of electrons on the nitrogen atoms and the π-system of the pyrenyl groups. Quenching by N,N-dialkylanilines indicates that steric interference reduces the energy gap between the locally-excited and exciplex species.

Excited state equilibria and geometrical effects during fluorescence quenching of sterically-graded pyrenes by tertiary aliphatic amines and N,N-dialkylanilines

254th National Meeting (2017)

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