Magnetic field effects on intramolecular exciplex fluorescence of chain-linked phenanthrene and N,N-dimethylaniline: Influence of chain length, solvent, and temperature

Magnetic field effects (MFEs) on the intramolecular exciplex fluorescence of a chain-linked phenanthrene (Phen)/N, N-dimethylaniline (DMA) system, Phen-(CH2)(n)-O-(CH2)(2)-DMA, have been studied in the magnetic fields (less than or equal to 0.62 T) as functions of (1) solvent polarity (epsilon=7.6-36.7), (2) chain length (n=4-12), and (3) temperature (223-333 K). The MFEs on the exciplex fluorescence are attributable to the singlet-triplet intersystem crossing in the intramolecular radical ion pair which is in dynamic equilibrium with the exciplex. (1) Solvent polarity increases significantly the MFEs on the exciplex fluorescence of Phen-(CH2)(10)-O-(CH2)(2)-DMA. This is attributable to the stability of the intramolecular radical ion pair relative to the exciplex. (2) A remarkable influence of chain length on MFEs in the exciplex fluorescence in N, N-dimethylformamide (DMF) was observed. The results were discussed in connection with the edge-to-edge distances [r] of two radicals obtained from molecular dynamics calculation for model compounds. (3) The temperature-induced high-field shift of the exchange energies \2J\ for Phen-(CH2)(4)-O-(CH2)(2)-DMA in DMF was discussed in connection with [r]