ELECTRONIC-SPECTRA AND EXCITED-STATE DYNAMICS OF VAN-DER-WAALS CLUSTERS OF ANTHRACENE WITH ALIPHATIC AND AROMATIC ETHERS - DEPENDENCE OF EXCIPLEX FORMATION ON DONOR (ETHER) IONIZATION-POTENTIAL

We have carried out a systematic study of exciplex formation from phot oexcited van der Waals complexes of anthracene with a variety of ether s, under collision-free conditions of a supersonic jet. Unlike some of the previously reported results, we have observed only narrow bands i n the fluorescence excitation spectra. The exciplex fluorescence was o bserved only from the complex containing donor moiety with the lowest ionization potential (viz., 1,4-dimethoxybenzene), thus providing clea r evidence for the dependence of exciplex formation on the ionization potential of the donor (ether) moiety. These results indicate that the energy of the charge transfer state relative to that of the initially prepared locally excited state determines the efficiency of the excip lex formation. In contrast to the previous report of exciplex formatio n in anthracene/diethyl ether and anthracene/anisole systems, we have observed only van der Waals type emissions from the locally excited st ates.