Two‐Photon STED Spectral Determination for a New V‐Shaped Organic Fluorescent Probe with Efficient Two‐Photon Absorption

Abstract

Two-photon stimulated emission depletion (STED) cross sections were determined over a broad spectral range for a novel two-photon absorbing organic molecule, representing the first such report. The synthesis, comprehensive linear photophysical, two-photon absorption (2PA), and stimulated emission properties of a new fluorene-based compound, (E)-2-(3-(2-(7-(diphenylamino)-9,9-diethyl-9H-fluoren-2-yl)vinyl)-5-methyl-4-oxocyclohexa-2,5-dienylidene) malononitrile (1), are presented. Linear spectral parameters, including excitation anisotropy and fluorescence lifetimes, were obtained over a broad range of organic solvents at room temperature. The degenerate 2PA spectrum of 1 was determined with a combination of the direct open aperture Z-scan and relative two-photon induced fluorescence methods using 1 kHz femtosecond excitation. The maximum value of 2PA cross section ~ 1700 GM was observed in the main, long wavelength, one-photon absorption band. One- and two-photon stimulated emission spectra of 1 were obtained over a broad spectral range using a femtosecond pumpprobe technique, resulting in relatively high two-photon stimulated emission depletion cross sections (~1200 GM). A potential application of 1 in bioimaging was demonstrated via one- and two-photon fluorescence microscopy images of HCT 116 cells incubated with micelle-encapsulated dye.

Transient Excited-State Absorption and Gain Spectroscopy of a Two-Photon Absorbing Probe with Efficient Superfluorescent Properties

“…(5) with the parameters μ 01 = 14.5 D, Γ 01 = 0.2 eV, μ 1 f = 10 D, Γ 0 f = 0.25 eV, and β = 0, which were in good agreement with the corresponding values obtained from quantum-chemical calculations and separate experimental methods. The high fluorescence quantum yield, acceptable 2PA cross-sections, and photochemical stability afford a relatively high figure of merit, 3 F M = Φ· δ 2 PA /Φ Ph ~ 10 5 –10 6 , which is comparable with typical fluorescence labels 3,10 and reflect good prospects of 1 for use in 2PFM.…”

Near-Infrared-Emitting Squaraine Dyes with High 2PA Cross-Sections for Multiphoton Fluorescence Imaging

“…33–37 Time-dependent absorption spectra upon irradiation at 650 NM were obtained with an Agilent 8453 UV/Vis spectrophotometer and photodecomposition quantum yields were determined.…”

Computer aided chemical design: using quantum chemical calculations to predict properties of a series of halochromic guaiazulene derivatives

“…It is possible that change of the solvent from methanol to dichloromethane (DCM) is responsible for the discrepancy: DCM can promote photooxidation and C–Cl bonds can be broken using UV light, leading to reactive species and additional damage to the compound in solution [21]. In the case of 3aH+ , longer wavelength light was used, thus avoiding the degradation of the solvent, and obtaining a value similar to those of other fluorescent dyes that have been previously reported [22]. …”

“…Among potential spacers, phenyl rings offer a greater degree of rigidity over polyene groups; compared with these spacers, the fluorene moiety can be a better alternative as it confers higher rigidity given the bridging carbon in the 9-position. Alternatively, the use of thiophene, an isostere of benzene, is shown to result in a bathochromic shift of the linear absorption spectrum [21,22]. The length of conjugation is known to shift the absorption spectrum, but it can also lead to increased two-photon absorption cross-sections [23,24].…”