One- and Two-Photon Stimulated Emission Depletion of a Sulfonyl-Containing Fluorene Derivative

One- and two-photon stimulated emission transitions were investigated by the fluorescence quenching of a sulfonyl-containing fluorene compound, 2,7-bis(4-(phenylsulfonyl)styryl)-9,9-didecyl-9H-fluorene (1), in solution at room temperature using a picosecond pump-probe technique. The nature of stimulated transitions under various fluorescence excitation and quenching conditions was analyzed theoretically, and good agreement with experimental data was demonstrated. Two-photon stimulated transitions S1f S0 were shown for 1 at λq) 1064 nm, representing the first report of two-photon stimulated emission depletion (STED) in a molecular system. The two-photon stimulated emission cross section, δ2PE(λq), of fluorene 1 was estimated to be ∼240-280 GM, suggesting that this compound may be a good candidate for use in two-photon STED microscopy. 1

Nature of Fast Relaxation Processes and Spectroscopy of a Membrane-Active Peptide Modified with Fluorescent Amino Acid Exhibiting Excited State Intramolecular Proton Transfer and Efficient Stimulated Emission

A fluorescently labeled peptide that exhibited fast excited state intramolecular proton transfer (ESIPT) was synthesized, and the nature of its electronic properties was comprehensively investigated, including linear photophysical and photochemical characterization, specific relaxation processes in the excited state, and its stimulated emission ability. The steady-state absorption, fluorescence, and excitation anisotropy spectra, along with fluorescence lifetimes and emission quantum yields, were obtained in liquid media and analyzed based on density functional theory quantum-chemical calculations. The nature of ESIPT processes of the peptide’s chromophore moiety was explored using a femtosecond transient absorption pump-probe technique, revealing relatively fast ESIPT velocity (∼10 ps) in protic MeOH at room temperature. Efficient superluminescence properties of the peptide were realized upon femtosecond excitation in the main long-wavelength absorption band with a corresponding threshold of the pump pulse energy of ∼1.5 μJ. Quantum-chemical analysis of the electronic structure of the peptide was performed using the density functional theory/time-dependent density functional theory level of theory, affording good agreement with experimental data

Two-Photon Fluorescence Microscopy Imaging of Cellular Oxidative Stress Using Profluorescent Nitroxides

A range of varying chromophore nitroxide free radicals and their nonradical methoxyamine analogues were synthesized and their linear photophysical properties examined. The presence of the proximate free radical masks the chromophore’s usual fluorescence emission, and these species are described as profluorescent. Two nitroxides incorporating anthracene and fluorescein chromophores (compounds 7 and 19, respectively) exhibited two-photon absorption (2PA) cross sections of approximately 400 G.M. when excited at wavelengths greater than 800 nm. Both of these profluorescent nitroxides demonstrated low cytotoxicity toward Chinese hamster ovary (CHO) cells. Imaging colocalization experiments with the commercially available CellROX Deep Red oxidative stress monitor demonstrated good cellular uptake of the nitroxide probes. Sensitivity of the nitroxide probes to H2O2-induced damage was also demonstrated by both one- and two-photon fluorescence microscopy. These profluorescent nitroxide probes are potentially powerful tools for imaging oxidative stress in biological systems, and they essentially “light up” in the presence of certain species generated from oxidative stress. The high ratio of the fluorescence quantum yield between the profluorescent nitroxide species and their nonradical adducts provides the sensitivity required for measuring a range of cellular redox environments. Furthermore, their reasonable 2PA cross sections provide for the option of using two-photon fluorescence microscopy, which circumvents commonly encountered disadvantages associated with one-photon imaging such as photobleaching and poor tissue penetration

Singlet Oxygen Quantum Yield Determination For A Fluorene-Based Two-Photon Photosensitizer

The quantum yield, Φ Δ, of singlet oxygen generation under two-photon excitation has been determined for a fluorene derivative. A photochemical method was developed using 1,3-diphenylisobenzofuran (DPBF), a chemical quencher of 1O 2, and 2-(9,9-didecyl-7- nitrofluoren-2-yl)benzothiazole (1) as a two-photon photosensitizer (PS). The photochemical kinetics of the quencher was measured by two different fluorescence methods. Fluorene 1 exhibited relatively high singlet oxygen quantum yield, Φ Δ∈≈∈0.4∈±∈0. 1, and had a two-photon absorption cross-section of 28∈±∈5GM. Thus, 1 may have potential for use as a two-photon PS in the near-IR spectral region for biomedical applications. © 2006 Springer Science+Business Media, Inc

Two-Photon Absorbing Photonic Materials: From Fundamentals To Applications

This chapter first reviews the fundamental aspects of the two-photon absorbing materials developed in our group. The design strategies and syntheses of a variety of fluorene-based conjugated molecules as two-photon absorbing materials, along with their photochemical and photophysical properties are described. The methodology of synthesis of these 2PA chromophores designed with various donor or acceptor groups, conjugation lengths and symmetries and the effects of the structure on the 2PA properties are demonstrated. This is followed by presentation of detailed studies of their linear absorption, steady-state and time-resolved fluorescence, fluorescence life time and anisotropy, excited-state absorption, and two-photon absorption measurements. The photostabilities of these chromophores are also investigated due to importance of this parameter in several emerging applications. The last part of the chapter provides a description of the application of these materials in fluorescence imaging, 3D data storage, photodynamic therapy, and 3D microfabrication. © 2008 Springer-Verlag

Photophysical And Photochemical Properties Of 5,7-Di-Methoxycoumarin Under One- And Two-Photon Excitation

The spectroscopic and photochemical properties of 5,7-dimethoxycoumarin (DMC) in acetonitrile (ACN) were investigated at room temperature under one- and two-photon excitation. Two-photon induced [2 + 2] photocycloaddition of DMC was investigated with 650 nm laser excitation (120 fs pulse width). GC and GC-MS analysis confirmed dimer formation, while HPLC analysis allowed specific photodimer identification through comparison with samples prepared via one photon irradiation. Photodimer products formed via two-photon excitation correlated with those formed via UV irradiation. Syn head-to-head and syn head-to-tail photodimers were formed in 1:3.0 and 1:2.8 ratios under one-photon (broadband UV) and two-photon (650 nm, 120 fs) irradiation in anisole, respectively. The quantum yield for the photoreaction of DMC solution (10-4 M) under broadband UV irradiation was of the order of 1 × 10-3 and increased dramatically to 1 × 10-2 under two-photon excitation. The spectral investigation of the photochemical products of DMC revealed efficient fluorescence emission in the spectral region 290-340 nm, attributed to the syn-head-to-tail dimers of DMC. Evidence for an additional manifold for the photochemical reaction of DMC was found, resulting in the production of photochemical products that exhibited low fluorescence emission intensity along with dependences on excitation wavelength. Copyright © 2002 John Wiley & Sons, Ltd

Excited-State Absorption And Anisotropy Properties Of Two-Photon Absorbing Fluorene Derivatives

The electronic structure of fluorene derivatives N-(7-benzothiazol-2-yl-9,9-bis-decyl-9H-fluoren-2-yl)-acetamide (1); 9,9-didecyl-2,7-bis-(N,N-benzothiazoyl)fluorene (2); 4,4′-{[9,9-bis(ethyl)-9H-fluorene-2,7-diyl]di-2,1-ethenediyl}bis(N, N-diphenyl)benzeneamine(3); and4,4′,4″([9,9-bis(ethyl)-9H-fluorene-2,4,7-triyl]tri-2, 1-ethenediyl}tris(N,N-diphenyl)benzeneamine (4) were investigated by a steady-state spectral technique, quantum-chemical calculations, and a picosecond pump-probe method. These derivatives are of interest for their relatively high two-photon absorption. The steady-state excitation anisotropy spectra reveal the nature of the ground-state absorption bands. Semiempirical quantum-chemical calculations of the fluorene derivatives (AMI, ZINDO/S) show good agreement with experimental data. The spectral positions and alignment of various electronic transitions of derivatives 1-4 were estimated from their excited-state absorption and anisotropy spectra. © 2005 Optical Society of America

A New Blue Light-Emitting Oligofluorene Glass: Synthesis, Characterization And Photophysical Properties

The synthesis, electrochemical, thermal and spectroscopic properties of the oligoaminofluorene derivative 9,9-didecyl-N,N-bis(9,9-didecyl-7-N,N-diphenylaminofluoren-2-yl)-N,N-diphenylflu orene-2,7-diamine (4), an organic glass, were investigated in solvents of differing polarity at room and 77 K temperature, including quantum yield and lifetime. The oligomer exhibited a glass transition near room temperature and was thermally stable to ca 400°C. Intramolecular interactions between the fluorenyl chromophores were investigated. The relatively complex nature of the emission band of 4 was characterized by reduced anisotropy and two components in its fluorescence decay at room temperature. Emission spectra of 4 at 77 K exhibited a single component in its fluorescence decay and a dependence on the excitation wavelength at the red edge of the absorption band. A spectroscopic model of 4 is proposed to explain the observed spectral behavior of this potentially important electroluminescent material. Copyright © 2003 John Wiley & Sons, Ltd

Photophysical Characterization, Two-Photon Absorption And Optical Power Limiting Of Two Fluorenylperylene Diimides

Perylene diimides have unique optical and electronic properties and have attracted interest in fields ranging from nonlinear optics to photovoltaics. The steady-state linear photophysical properties, two-photon absorption (2PA) spectra, and optical limiting behavior of fluorenylperylene diimide-based derivatives were investigated in solution at room temperature. An efficient intramolecular energy transfer and specific strong dependences of fluorescence quantum yield on solvent properties were observed. The 2PA spectra were measured over a broad spectral region by two-photon induced fluorescence and open aperture Z-scan methods under femtosecond and picosecond excitation, respectively. The maximum values of pure 2PA cross sections, up to ∼3500 GM, were obtained for fluorenylperylene diimide-based derivatives under picosecond excitation, when excited-state absorption and stimulated emission processes were taken into account. These perylene derivatives exhibited efficient two-photon optical power limiting under picosecond excitation. © 2008 American Chemical Society