Two-photon Cross Section Enhancement of Photochromic Compounds for Use in 3D Optical Data Storage

Rewritable photochrome-based 3D optical data storage requires photochromic molecules with high two-photon absorption (2PA) cross sections. Currently, the low value of two-photon absorption cross sections of existing photochromes makes them unsuitable for practical application in 3D data storage. Worldwide attempts to increase the cross section of photochromic molecules by altering the chemical structure have yielded poor results. In this work, two ways to increase the two-photon absorption cross sections of photochromes were investigated. In the first method, partial success demonstrated by extending the conjugation of a photochromic molecule, a high two-photon absorption cross section of the closed form isomer and high photoconversion to the closed form were realized. At the same time, a decrease in photoswitching quantum yield and low photoconversion to open form was observed. A discussion is provided to explain the results, suggesting that the proposed method of extending the conjugation may not solve the problem. For this reason a new method for effective two-photon absorption cross section enhancement of photochromes was proposed. As a proof of principle, a new two-photon absorbing dye with a hydrogen bonding moiety was synthesized and used for the formation of supramolecular structures with a photochromic compound. Theoretical reasoning and experimental demonstration of energy transfer from the dye to the photochrome under one and two-photon excitation confirmed the practical value of the method. The effects of a 2PA dye on the photochromic properties of a diarylethene were investigated using a model compound to simplify data analysis. Formation of supramolecular structures was revealed using ¹H NMR spectroscopic methods. The model compound, having the same hydrogen bonding moiety as 2PA dye, has been demonstrated to bind with photochrome molecules at very low concentrations. Photochromic properties of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleimide, including conversions at the photostationary state, extinction coefficients, photoisomerization reaction rates and quantum yields, were shown to be affected by hydrogen bonding with the model compound - 2,6-bis-(acetamido)pyridine. The extent of this change was determined and discussed, demonstrating a balanced supramolecular strategy to modulate photochemical and photophysical properties of this important class of photochromic material

Two-Photon Absorption And Time-Resolved Stimulated Emission Depletion Spectroscopy Of A New Push-Pull Fluorene Derivative

The STED properties of a new fluorene derivative were investigated by a fluorescencequenching femtosecond technique along with the comprehensive linear photophysical, photochemical, and 2PA characterizations. Potential application ofin bioimaging was shown via 2PFM. ©2013 The Optical Society (OSA)

Photosensitive Polymeric Materials For Two-Photon 3D Worm Optical Data Storage Systems

We report the photochemistry and development of a fluorescence readout-based, nonlinear absorption, three-dimensional optical data storage system. In this system, writing was achieved by acid generation upon two-photon absorption (2PA) of a photoacid generator (PAG; at 710 or 730 nm). Readout was then performed by interrogating two-photon-absorbing dyes, after protonation, at 860 nm. Linear and nonlinear photophysical characterization of 2PA PAGs and acid-sensitive fluorescent dyes demonstrates good spectral resolution between the PAG and protonated 2PA dye and relatively high two-photon absorptivity. Solution spectroscopic studies confirm photoacid generation and dye protonation. Two-photon recording and readout of voxels were demonstrated in five and eight consecutive, crosstalk-free layers within a polymer matrix, generating a data storage capacity of up to 1.8 × 10 13 bits/cm 3. © 2009 American Chemical Society

Superfluorescent Squaraine With Efficient Two-Photon Absorption And High Photostability

The synthesis, linear photophysical, two-photon absorption (2PA), femtosecond transient absorption, and superfluorescence properties of a new symmetrical squaraine derivative (1) are reported. Steady-state linear spectral and photochemical properties, fluorescence lifetimes, and excitation anisotropy of 1 were investigated in various organic solvents. High fluorescence quantum yields (≈0.7) and very high photostability (photodecomposition quantum yields ≈10-6-10-8) were observed. An open-aperture Z-scan method was used to obtain 2PA spectra of 1 over a broad spectral range (maximum 2PA cross section ≈1000 GM). Excited-state absorption (ESA) and gain was observed by femtosecond transient absorption spectroscopy, in which both reached a maximum at approximately 500 fs. Squaraine 1 exhibits efficient superfluorescence. The quantum chemical study of 1 revealed the simulated vibronic nature of the 1PA and 2PA spectra were in good agreement with experimental data; this may provide the ability to predict potential advanced photonic materials. Super fluoro to the rescue! Large two-photon absorption (2PA), femtosecond transient absorption kinetics, and efficient superfluorescence properties of a new symmetrical squaraine derivative (1) are reported along with extremely high photochemical stability. The density functional theory (DFT)-based quantum chemical study of 1 reveals the vibronic nature of the 2PA spectra in the main linear absorption band that is in good agreement with experimental data. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Efficient Photochromic Transformation Of A New Fluorenyl Diarylethene: One- And Two-Photon Absorption Spectroscopy

Efficient reversible phototransformation of a new diarylethene-fluorene derivative, 1,2-bis(5-(9,9-didecyl-7-nitro-9H-fluoren-2-yl)-2-methylthiophen-3- yl)cyclopent-1-ene (1), was demonstrated in organic media under low-intensity laser excitation. Linear photophysical characterization of 1 was performed at room temperature in solvents of different polarity and viscosity. Significantly, close to unity quantum yield for the cyclization reaction of 1 was shown in nonpolar solutions. The lifetimes of the excited states of the open (OF) and closed (CF) forms of 1 were measured by a femtosecond transient absorption technique, and corresponding values of ∼0.7 and ∼0.9 ps were shown in dichloromethane (DCM), respectively. Degenerate two-photon absorption (2PA) spectra of the OF and CF of 1 were obtained over a broad spectral range by the open aperture Z-scan method under 1 kHz femtosecond excitation. The values of 2PA cross sections of the OF in DCM (∼50-70 GM) were found to increase up to 1 order of magnitude (∼600 GM) after cyclization to the CF. The nature of cyclization and cylcoreversion processes were investigated by quantum chemistry with employment of DFT-based methods implemented in the Gaussian\u2709 program. The potential of 1 for application in optical data storage was shown using poly(methyl methacrylate)-doped films and two-photon fluorescence microscopy readout. © 2011 American Chemical Society

Linear And Nonlinear Photophysics And Bioimaging Of An Integrin-Targeting Water-Soluble Fluorenyl Probe

Linear photophysical characterization and two-photon absorption (2PA) properties of a new water-soluble fluorene derivative, 3-(9-(2-(2-methoxyethoxy) ethyl)-2,7-bis{3-[2-(polyethyleneglycol-550-monomethylether-1-yl)]-4-(benzo[d] thiazol-2-yl)styryl}-9H-fluoren-9-yl)propanoic acid (1), were investigated in several organic solvents and water at room temperature. A comprehensive analysis of the steady-state absorption, emission and excitation anisotropy spectra revealed electronic structures of 1, including mutual orientation of the transition dipoles, relatively weak solvatochromic effects, high fluorescence quantum yield (∼0.5-1.0), and strong aggregation in water. The 2PA spectra of 1 were obtained in the 600-900 nm spectral range by two-photon induced fluorescence (2PF) and open aperture Z-scan methods using femtosecond laser sources. No discrete 2PA bands were apparent and values of the corresponding 2PA cross sections monotonically increased in the short wavelength range up to 3000 GM in organic solvents and ∼6000 GM in aqueous solution, reflecting relatively high two-photon absorptivity. The 2PA efficiency of 1 in water increased 2-3 times relative to aprotic solvents and can be explained by cooperative electronic effects of molecular aggregates of 1 produced in aqueous media. The carboxylic acid fluorenyl probe 1 was conjugated with the cyclic peptide RGDfK. Two-photon fluorescence microscopy (2PFM) imaging of U87MG cells (and MCF-7 as control), incubated with fluorene-RGD peptide conjugate 2, demonstrated high αvβ3 integrin selectivity, making this probe particularly attractive for integrin imaging. © The Royal Society of Chemistry 2010

Transient Excited-State Absorption And Gain Spectroscopy Of A Two-Photon Absorbing Probe With Efficient Superfluorescent Properties

Atomistic simulations reveal that the chemical reactivity of ceria nanorods is increased when tensioned and reduced when compressed promising strain-tunable reactivity; the reactivity is determined by calculating the energy required to oxidize CO to CO 2 by extracting oxygen from the surface of the nanorod. Visual reactivity fingerprints , where surface oxygens are colored according to calculated chemical reactivity, are presented for ceria nanomaterials including: nanoparticles, nanorods, and mesoporous architectures. The images reveal directly how the nanoarchitecture (size, shape, channel curvature, morphology) and microstructure (dislocations, grain-boundaries) influences chemical reactivity. We show the generality of the approach, and its relevance to a variety of important processes and applications, by using the method to help understand: TiO 2 nanoparticles (photocatalysis), mesoporous ZnS (semiconductor band gap engineering), MgO (catalysis), CeO 2/YSZ interfaces (strained thin films; solid oxide fuel cells/nanoionics), and Li-MnO 2 (lithiation induced strain; energy storage). © 2012 American Chemical Society

Two-Photon Absorption And Time-Resolved Stimulated Emission Depletion Spectroscopy Of A New Fluorenyl Derivative

The synthesis, comprehensive linear photophysical characterization, two-photon absorption (2PA), steady-state and time-resolved stimulated emission depletion properties of a new fluorene derivative, (E)-1-(2-(di-p-tolylamino)-9, 9-diethyl-9H-fluoren-7-yl)-3-(thiophen-2-yl)prop-2-en-1-one (1), are reported. The primary linear spectral properties, including excitation anisotropy, fluorescence lifetimes, and photostability, were investigated in a number of aprotic solvents at room temperature. The degenerate 2PA spectra of 1 were obtained with open-aperture Z-scan and two-photon induced fluorescence methods, using a 1 kHz femtosecond laser system, and maximum 2PA cross-sections of ∼400-600 GM were obtained. The nature of the electronic absorption processes in 1 was investigated by DFT-based quantum chemical methods implemented in the Gaussian 09 program. The one- and two-photon stimulated emission spectra of 1 were measured over a broad spectral range using a femtosecond pump-probe-based fluorescence quenching technique, while a new methodology for time-resolved fluorescence emission spectroscopy is proposed. An effective application of 1 in fluorescence bioimaging was demonstrated by means of one- and two-photon fluorescence microscopy images of HCT 116 cells containing dye encapsulated micelles. The one- and two-photon stimulated emission spectra of a new fluorene derivative, (E)-1-(2-(di-p-tolylamino)-9,9-diethyl-9H-fluoren-7-yl)-3-(thiophen- 2-yl)prop-2-en-1-one are obtained over a broad spectral range (see picture) and a new methodology for time-resolved fluorescence emission spectroscopy is proposed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim