A Facile Molecular Machine: Optically Triggered Counterion Migration by Charge Transfer of Linear Donor-π-Acceptor Phosphonium Fluorophores

Research output: Contribution to journalArticle


  • Andrey Belyaev
  • Yu Hsuan Cheng
  • Zong Ying Liu
  • Antti Karttunen

  • Pi Tai Chou
  • Igor O. Koshevoy

Research units

  • University of Eastern Finland
  • National Taiwan University


The D-π-A type phosphonium salts in which electron acceptor (A=-+PR3) and donor (D=-NPh2) groups are linked by polarizable π-conjugated spacers show intense fluorescence that is classically ascribed to excited-state intramolecular charge transfer (ICT). Unexpectedly, salts with π=-(C6H4)n- and -(C10H6C6H4)- exhibit an unusual dual emission (F1 and F2 bands) in weakly polar or nonpolar solvents. Time-resolved fluorescence studies show a successive temporal evolution from the F1 to F2 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.


Original languageEnglish
JournalAngewandte Chemie - International Edition
Publication statusPublished - 1 Jan 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • charge transfer, donor–acceptor systems, dual emission, fluorescence, ion migration

ID: 36621366