Intramolecular exciplex formation in 1-(1-pyrenyl)-3-N,N-dimethylaminophenylpropane (I) and its derivatives with one (II) and two (III) ester substituent(s) at the 2-position of the propane linkage has been studied in isooctane. Introduction of the two bulky ester groups (i.e. III) is characterized by a large decrease in the quantum yield of exciplex formation as well as by the appearance of two rise components of exciplex emission (4.2 and 24.1 ns at 35°C). Extremely slow rise time and low quantum yield of exciplex emission in III are explained by steric hindrance of the bulky ester groups for the structural change from (tt) to (tg±) and from (tg±) to (g±g∓) conformers in the excited singlet state.
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