Study of energy transfer in a naphthalene-linked crown ether–Eu3+ complex: the effect of the orientation of the naphthalene π-plane with respect to the Eu3+ ion

The energy transfer (ET) from naphthalene (N) to Eu3+ has been studied in complexes of the Eu3+ ion with 2,3-naphtho-17-crown-5, 2,3-naphtho-20-crown-6, 1,8-naphtho-21-crown-6 and 1,5-naphtho-22-crown-6, respectively, using the NO3− ion as the counter anion in EtOH glass at 77 K. Both the ET efficiency and the N-phosphorescence quenching show a strong dependence on the orientation of the N–π-plane with respect to the Eu3+ ion. The results suggest that an exchange mechanism involving the lowest excited triplet state of N and 5D2 states of the rare-earth ions is mainly operating.