Steady-state and femtosecond transient absorption spectroscopy of new two-photon absorbing fluorene-containing quinolizinium cation membrane probes

Xiling Yue, Zach Armijo, Kevan King, Mykhailo V. Bondar, Alma R. Morales, Andrew Frazer, Ivan A. Mikhailov, Olga V. Przhonska, Kevin D. Belfield

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


The synthesis, linear photophysical characterization, and nonlinear optical properties of two new symmetrical fluorene-containing quinolizinium derivatives, 2,8-bis((E)-2-(7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl)vinyl)quinolizinium hexafluorophosphate (1) and 2,8-bis((E)-2-(7-((7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl)ethynyl)-9,9-dihexyl-9H-fluoren-2yl)vinyl)quinolizinium hexafluorophosphate (2), are reported. The nature of the dual-band steady-state fluorescence emission of 1 and 2 was determined, and violation of Kashas rule along with a strong dependence on solvent polarity were shown. A relatively complex structure of two-photon absorption (2PA) spectra of 1 and 2, with maximum cross sections of ∼400-600 GM, was determined using the open aperture Z-scan method. Different types of fast relaxation processes with characteristic times of 0.3-0.5 ps and 1.5-2 ps were observed in the excited states of the new compounds via femtosecond transient absorption pump-probe spectroscopy. To better understand the photophysical behavior of 1 and 2, a quantum-mechanical study was undertaken using TD-DFT and ZINDO/S methods. Simulated linear absorption spectra were found to be in good agreement with experimental data, while 2PA cross sections were overestimated. Although the new dyes were highly fluorescent in nonpolar solvents, they were essentially nonfluorescent in polar media. Significantly, the quinolizinium dyes exhibited fluorescence turn-on behavior upon binding to bovine serum album (BSA) protein, exhibiting over 4-fold fluorescence enhancement, which was a finding that was leveraged to demonstrate cell membrane fluorescence imaging of HeLa cells.

Original languageEnglish (US)
Pages (from-to)2833-2846
Number of pages14
JournalACS Applied Materials and Interfaces
Issue number4
StatePublished - Feb 4 2015

All Science Journal Classification (ASJC) codes

  • General Materials Science


  • femtosecond transient absorption spectroscopy
  • fluorescence bioimaging
  • fluorescence probes
  • quinolizinium derivatives
  • two-photon absorption


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