Two-photon Excited Fluorescence Method Research Articles

Two-photon absorption characterization and comparison of Au(I) fluorenyl benzothiazole complexes in the visible wavelength regime

We use the two-photon excited fluorescence method to determine the two-photon absorption (2PA) cross sections of three series of (fluorenyl benzothiazole) gold(I) complexes in the visible wavelength range from 570 to 700 nm. We compare the effect of ancillary ligand substitutions on the 2PA magnitudes and find that the ancillary ligand does not drastically affect either the magnitude or the shape of 2PA. Even so, moderate 2PA cross sections were measured that ranged from 10 to 1000 s of GM (Göppert-Mayer, =10-50cm4s/photon), making these types of complexes nonlinear optical materials for two-photon absorbing applications.

Two-photon absorption cross-section results of three tri-branched derivatives: A comparison between open-aperture Z-scan and two-photon excited fluorescence method

Femtosecond open-aperture Z-scan and two-photon excited fluorescence method, were performed to study the two-photon absorption cross-section of several tri-branched derivatives. The two-photon absorption cross-section values measured by the two different methods were compared. Our results indicate that, the absolute values of the two-photon absorption cross-section measured by different technique are obviously different. The absorption cross-sections measured by two-photon excited fluorescence method exhibited 2.1–2.3 times larger than that measured by open-aperture Z-scan method. And the difference is most likely caused by the system error of different measurements. Our results may provide scientific responsible reference as well as some useful information for the comparison of the two-photon absorption cross-section values measured by different methods.

Strong fluorescence following two-photon excitation in fully conjugated oxadiazole-based oligoaryl

Highly fluorescent oxadiazole-based chromophore with alternating alkoxy benzene and thiophene moieties has been designed and synthesized, and large two-photon absorption (TPA) cross section in near infrared (NIR) region was performed. DFT calculation predicted fully π-conjugation among molecular skeleton and minor behavior of intra-molecular charge transfer (ICT). The solvent dependent emission spectra also suggested the occurrence of ICT was trivial, although oxadiazole was electron deficient and alkoxy benzene was electron rich. On the other hand, the resulting chromophore exhibited fluorescence quantum yield up to 75% because of the incorporation of oxadiazole. The quadratic dependence of emission intensity on input excitation power indicated TPA mechanism under irradiation of NIR laser. Based on two-photon excited fluorescence method, the designed fluorophore exhibited the largest TPA cross section (620GM) at 850nm. The cooperative phenomena of large TPA response and strong fluorescence output in this designed molecule might ensure a potential use for application of two-photon excited light-emitting materials.

A series of water-soluble A-π-A' typological indolium derivatives with two-photon properties for rapidly detecting HSO3 -/SO3 2- in living cells.

It is believed that HSO3 - and SO3 2- play important roles in several physiological processes. However, probes with two-photon absorption to detect HSO3 - or SO3 2- in living cells are still limited. Herein, a series of novel indolium derivatives (L1-L4) with an A-π-A' structure was designed and synthesized as ratiometric probes to detect HSO3 -/SO3 2-in vitro. L3 and L4 display a colorimetric and ratiometric fluorescence dual response to HSO3 -/SO3 2- with a very fast (∼15 s) and high specificity, as well as low detection limits (∼22 nM). Furthermore, their detection is also carried out by using a two-photon excited fluorescence method. A nucleophilic addition reaction is proposed for the sensing mechanism, which is supported by MS, 1H NMR, and density functional theory (DFT) investigations. Importantly, L3 was successfully used for detecting intrinsically generated intracellular HSO3 -/SO3 2- in cancerous cells under one- and two-photon excited fluorescence imaging.

Small water-soluble pyrimidine hexafluorophosphate derivatives with high two-photon absorption activities in the near-IR region and their biological applications

Two imidazole–pyrimidine hexafluorophosphate derivatives (6P and 10P) are synthesized. The 2PA cross-section values (σ) were obtained by Z-scan and two-photon excited fluorescence methods. 6P and 10P can be used to quantify and image organelles in living cells and tissues.

Synthesis and Linear and Nonlinear Optical Properties of Three Push-Pull Oxazol-5(4H)-one Compounds.

Three uncharged push-pull oxazol-5(4H)-ones were synthesized and thoroughly characterized. The examined molecules contained electron-donor and electron-acceptor groups interacting via a π-conjugated bridge. Spectral properties of the oxazol-5(4H)-ones were studied in detail in three solvents of different polarities. The results indicate a solvatochromic shift toward lower energy for the charge-transfer state. The compounds are weakly fluorescent in polar solvents, but they have high fluorescence quantum yields in nonpolar solvents. Their two-photon absorption (2PA) properties were characterized by the open- and closed-aperture Z-scan technique, by the pump-probe technique, and by the two-photon excited fluorescence method. The dyes exhibit relatively high effective two-photon absorption cross sections ranging from 490 to 2600 GM at ~100 GW/cm(2), according to the Z-scan results, which are found, however, to contain significant contribution from higher-order absorption processes. In addition, these compounds display good photostability.

Two-photon absorption and optical power limiting properties of ladder-type tetraphenylene cored chromophores with different terminal groups

A series of soluble ladder-type tetraphenylene cored chromophores with different terminal groups have been synthesized and their structure–property relationship with regards to various linear optical and nonlinear optical properties has been established. By using the two-photon excited fluorescence method and the nonlinear transmission method, the two-photon absorption (2PA) properties of these chromophores were determined, and they were found to be strongly dependent on the electron-richness of the ladder-type tetraphenylene core, as well as the terminal groups. The introduction of strong electron donors (N-alkyl) in both the central core and the terminals led to a chromophore with a high 2PA cross-section value of 2137 GM. Optical limiting behaviors of the synthesized chromophores in THF were investigated by using a femto-second ultra-fast laser. 2PA coefficients for these chromophores in THF (5 mM) ranged from 0.131–0.256 cm GW−1. The ladder-type tetraphenylene cored chromophore with the highest 2PA cross-section value exhibited the best optical limiting performance, as evidenced by light transmission as low as 19.1% at 770 nm under an intensity of 99.6 GW cm−2. The excellent optical limiting performance of these chromophores makes them useful in photonic or optoelectronic devices for protecting human eyes and optical sensors, as well as for stabilizing light sources in optical communications.

Synthesis and Photophysical Properties of Two-Photon Absorbing Spirofluorene Derivatives

New spirofluorene-based quadrupolar two-photon absorbing dyes having triphenylamine and N,N-dibutylaniline as electron donors at the end of molcules were designed and synthesized. The third-order nonlinear optical properties of these compounds were studied using a two-photon excited fluorescence method. They were found to have high two-photon absorption cross-section owing to extended conjugation of the spirofluorene moiety. The effect of varying the donor strength could be discerned by comparing the two compounds. They were successfully used as a photosensitizers for two-photon initiated polymerization of three-dimensional micro-objects.

Two-photon absorption properties of malononitrile derivatives

Two malononitrile derivatives, 2-[2,5-bis-(4-dimethylamino-benzylidene)-cyclopentylidene]-malononitrile ( 1) and 2-{2,6-bis-[2-(4-dimethylamino-phenyl)-vinyl]-pyran-4-ylidene}-malononitrile ( 2), were synthesized and their photophysical characteristics were investigated using UV–vis spectra, fluorescence spectra, nonlinear transmission and two-photon excited spectra. The results showed that both compounds exhibited strong intramolecular charge transfer absorption bands within 400–600 nm, but only compound 2 presented a strong fluorescence emission. By nonlinear transmission method, the two-photon absorption cross-section ( σ) values of two compounds were determined as 250 GM and 283 GM, respectively, with 800 nm femtosecond laser pulses. By two-photon excited fluorescence method, the two-photon excited spectra of compound 2 within 720–880 nm was measured and its σ max was obtained as 773 GM at 770 nm.

Two-photon-excited fluorescence measurements of OH concentration in a hydrogen–oxygen flame

Two-photon-excited fluorescence (TPF) has been used to determine the OH concentration profile in an atmospheric-pressure hydrogen–oxygen flame. Individual rovibronic transitions within the A2Σ+−X2Π (0,0) system of OH were identified by comparing calculated wavelengths to emission spectra obtained by laser excitation from 604 to 638 nm. Relative OH concentrations were determined by individually exciting the O1(5), O2(5), and P2(5) transitions and monitoring the resulting fluorescence with a filtered photomultiplier and a gated integrator system. The expected quadratic dependence of the fluorescence signal on laser power was verified indicating the probable lack of photochemical effects. The OH profile determined by the TPF method was found to be in good agreement with that determined by absorption spectroscopy. The estimated OH detection limit using TPF is ∼1014 molecules/cm3 at atmospheric pressure.