title: Steady-state and femtosecond transient absorption spectroscopy of new two-photon absorbing fluorene-containing quinolizinium cation membrane probes.
abstract: 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 Kasha's 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.
authors.affiliation: Department of Chemistry, University of Central Florida , P.O. Box 162366, Orlando, Florida 32816, United States.
authors.forename: Xiling
authors.initials: X
authors.lastname: Yue
authors.forename: Zach
authors.initials: Z
authors.lastname: Armijo
authors.forename: Kevan
authors.initials: K
authors.lastname: King
authors.forename: Mykhailo V
authors.initials: MV
authors.lastname: Bondar
authors.forename: Alma R
authors.initials: AR
authors.lastname: Morales
authors.forename: Andrew
authors.initials: A
authors.lastname: Frazer
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Mikhailov
authors.forename: Olga V
authors.initials: OV
authors.lastname: Przhonska
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Belfield
mesh_terms: D002412:Cations / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry*; D002477:Cells / Q000737:chemistry; D005449:Fluorenes / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D011807:Quinolizines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D002412:Cations; D005449:Fluorenes; D005456:Fluorescent Dyes; D011807:Quinolizines; C041509:fluorene
keywords: femtosecond transient absorption spectroscopy; fluorescence bioimaging; fluorescence probes; quinolizinium derivatives; two-photon absorption