期刊
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 58, 期 38, 页码 13456-13465出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201906929
关键词
charge transfer; donor-acceptor systems; dual emission; fluorescence; ion migration
资金
- Ministry of science and technology, Taiwan
- Academy of Finland [317903]
- Academy of Finland (AKA) [317903, 317903] Funding Source: Academy of Finland (AKA)
The D-pi-A type phosphonium salts in which electron acceptor (A=-+PR3) and donor (D=-NPh2) groups are linked by polarizable pi-conjugated spacers show intense fluorescence that is classically ascribed to excited-state intramolecular charge transfer (ICT). Unexpectedly, salts with pi=-(C6H4)(n)- and -(C10H6C6H4)- exhibit an unusual dual emission (F-1 and F-2 bands) in weakly polar or nonpolar solvents. Time-resolved fluorescence studies show a successive temporal evolution from the F-1 to F-2 emission, which can be rationalized by an ICT-driven counterion migration. Upon optically induced ICT, the counterions move from -+PR3 to -NPh2 and back in the ground state, thus achieving an ion-transfer cycle. Increasing the solvent polarity makes the solvent stabilization dominant, and virtually stops the ion migration. Providing that either D or A has ionic character (by static ion-pair stabilization), the ICT-induced counterion migration should not be uncommon in weakly polar to nonpolar media, thereby providing a facile avenue for mimicking a photoinduced molecular machine-like motion.
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