Showing papers by "Gagik G. Gurzadyan published in 2014"

Near-infrared fluorescence amplified organic nanoparticles with aggregation-induced emission characteristics for in vivo imaging.

Abstract: Near-infrared (NIR) fluorescence signals are highly desirable to achieve high resolution in biological imaging. To obtain NIR emission with high brightness, fluorescent nanoparticles (NPs) are synthesized by co-encapsulation of 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl)phenylamino)phenyl)fumaronitrile (TPETPAFN), a luminogen with aggregation-induced emission (AIE) characteristics, and a NIR fluorogen of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (NIR775) using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] as the encapsulation matrix. The good spectral overlap between the emission of TPETPAFN and the absorption of NIR775 leads to efficient energy transfer, resulting in a 47-fold enhancement of the NIR775 emission intensity upon excitation of TPETPAFN at 510 nm as compared to that upon direct excitation of NIR775 at 760 nm. The obtained fluorescent NPs show sharp NIR emission with a band width of 20 nm, a large Stokes shift of 275 nm, good photostability and low cytotoxicity. In vivo imaging study reveals that the synthesized NPs are able to provide high fluorescence contrast in live animals. The Forster resonance energy transfer strategy overcomes the intrinsic limitation of broad emission spectra for AIE NPs, which opens new opportunities to synthesize organic NPs with high brightness and narrow emission for potential applications in multiplex sensing and imaging.

Micelle/Silica Co-protected Conjugated Polymer Nanoparticles for Two-Photon Excited Brain Vascular Imaging

Abstract: Large two-photon absorption cross section and high fluorescence quantum yield (QY) of a fluorescent probe is highly desirable to achieve high resolution in two-photon excited fluorescence imaging. Taking poly(9,9-dihexylfluorene-alt-2,1,3-benzothiadiazole) (PFBT) as an example, we report a one-step approach to synthesize PFBT loaded nanoparticles (NPs) with both large two-photon absorption cross section and high fluorescence QY in aqueous media through a micelle and silica coprotection strategy. The PFBT loaded NPs show a two-photon absorption cross section of 1085 GM at 810 nm based on polymer chain concentration and an emission maximum at 545 nm with a high fluorescence QY of 75%. The fluorescence lifetime investigation reveals that the high fluorescence QY is mainly due to reduced polymer aggregation and minimized environment influence on conjugated polymer (CP) fluorescence quenching. The synthesized PFBT NPs have shown good colloid stability and photostability as well as benign biocompatibility, whic...

Solvent-Dependent Stoichiometry in Perylene–7,7,8,8-Tetracyanoquinodimethane Charge Transfer Compound Single Crystals

Abstract: Perylene forms three binary compounds with TCNQ. Using a physical vapor transport (PVT) method, mixtures of P1T1 (perylene1–TCNQ1), P2T1 (perylene2–TCNQ1), and P3T1 (perylene3–TCNQ1) crystals can be grown simultaneously. Solution-grown crystals exhibit a stoichiometry that depends on the solvent used and not on the initial stoichiometry of the perylene and TCNQ: only single crystals of P1T1 were grown from toluene, and only P3T1, from benzene. Precipitation–dissolution theory was employed to explain this phenomenon. We found that P1T1 is less soluble than P3T1 in toluene, which resulted in its preponderant growth from this solvent. Using the same argument, we could also explain the growth of P3T1 from benzene. Crystallization of P2T1 from solution was not possible. In addition, steady-state and time-resolved fluorescence measurements indicate that the difference in solubility of TCNQ in benzene and toluene leads to different fluorescence spectra due to selective crystallization of P1T1 and P3T1 from tolue...

Excited-state dynamics in an α-perylene single crystal: two-photon- and consecutive two-quantum-induced singlet fission.

Abstract: Excited-state dynamics in α-perylene single crystals is studied by time-resolved fluorescence and transient absorption techniques under different excitation conditions. The ultrafast lifetimes of the "hot" excimer (Y) state were resolved. Three competing excited-states decay channels are observed: excimer formation, dimer cation generation, and singlet fission. The singlet fission induced by two-photon and consecutive two-quantum absorption is reported for the first time in an α-perylene crystal.

Bright Quantum-Dot-Sized Single-Chain Conjugated Polyelectrolyte Nanoparticles: Synthesis, Characterization and Application for Specific Extracellular Labeling and Imaging

Abstract: We report a simple method to fabricate quantum-dot-sized nanoparticles (NPs) from poly[9,9-bis((6-N,N,N-trimethylammonium)hexyl)fluorene-alt-co-2,1,3-benzo-xadiazole dibromide] (PFBD). The transmission electron microscope results reveal that the obtained NPs have a mean diameter of ≈4 nm, which is composed of a single PFBD chain. The NPs show bright fluorescence with an emission maximum at ≈636 nm and a quantum yield of ≈26% in water. The fluorescence properties of the NPs are characterized by steady fluorescence microscopy, fluorescence dynamic study and single nanoparticle microscopy, which show superior brightness over commercial quantum dots QD655. The NPs are further conjugated with streptavidin to yield PFBD-SA NPs, which serve as a specific extracellular labeling and imaging probe with high specificity and good photostability.

Femtosecond pump–probe spectroscopy of graphene oxide in water

Abstract: Transient absorption properties of aqueous graphene oxide (GO) have been studied by use of femtosecond pump?probe spectroscopy. Excited state absorption and photobleaching are observed in the wide spectral range. The observed fast three lifetime components are attributed to the absorption of upper excited states and localized states, which is confirmed by both laser induced absorption and transmission kinetics. The longest time component is assigned to the lowest excited state of GO, which mainly originates from the sp2 domains. With the increase of the excitation power, two-quantum absorption occurs, which results in an additional rise-time component of the observed transients.

Ultrafast dynamics in molecules, nanostructures and interfaces : selected lectures presented at Symposium on Ultrafast Dynamics of the 7th International Conference on Materials for Advanced Technologies, Singapore, 30 June - 5 July 2013

Abstract: Fundamentals of Light - Matter Interaction: Ultrafast Dynamics in Correlated Electron Materials (Antoinette Taylor, Rohit Prasankumar, George Rodriguez, Dmitry Yarotski, Quanxi Jia and Stuart Trugman) Ultrafast Charge and Energy Transfer in Semiconductor-Metal Hybrid Nanoparticles (Paolo Maioli, D Mongin, V Juve, A Crut, N Del Fatti and F Vallee) Studies of Ultrafast Quantum Dynamics by Femtosedond to Attosecond XUV Absorption Spectroscopy (Zhi-Heng Loh) Biomaterials: Real-time Wavepacket Dynamics Through a Conical Intersection: The Primary Event of Vision (Giulio Cerullo) Ultrafast Transient Absorption and Polarized Light Spectroscopy Characterizing the Exciton Interactions in Chlorosomes (Alfred Holzwarth1, Marc Muller1, Petar Lambrev, Yulia Miloslavina, Krysztof Pawlak and Gyozo Garab) Coherent Multidimensional Spectroscopy of Excitons in Photosynthetic Complexes with Classical and Quantum Light (Shaul Mukamel, Frank Schlawin, Konstantin Dorfman and Benjamin Fingerhut) Switching Ability and Adaptation to Different External Conditions of Photosynthetic Proteins (Leonas Valkunas and Jevgenij Chmeliov) Ultrafast 2d and 3d Optical Spectroscopy - Its Implementation and Applications (Howe-Siang Tan) Organic Semiconductors: Simultaneous Measurement of Electronic and Vibrational Dynamics in a Polyacetylene Derivative Studied by a Few-cycle Pulse Laser (Takayoshi Kobayashi, Tsugumasa Iiyama, Kotaro Okamura and Toshio Masuda) Charge Generation and Recombination in Low-bandgap Polymer : Fullerene Photovoltaic Blends (Frederic Laquai, Ian Howard, Clare Dyer-Smith, Fabian Etzold and Julian Ochsmann) Charge Transfer Dynamics in Assemblies of Functional Molecules (Michael Zharnikov) Morphology of Bulk Heterojunction Revealed by Ultrafast Excitons (Maxim Pshenichnikov, Almis Serbenta, Vlad Pavelyev, Kees Hummelen and Paul van Loosdrecht1) Mechanisms of Charge Photogeneration in Polymer/fullerene Blends: Driving Force and Effect of Electric Field (Jianping Zhang) Time-Resolved Energy Transfer in Semiconducting Polymer Heterostructures (Caio Rimoli and Paulo Miranda) Charge Carrier Generation and Transport in Merocianine: Fullerene Blends for Solar Cells (Vidmantas Gulbinas) Inorganic Semiconductors and Nanostructures: Making Most of the Absorbed Photon: New Insights Into Carrier Multiplication in Semiconductor Nanostructures (Victor I Klimov) Mapping Carrier Diffusion in Single Silicon Core - Shell Nanowires with Ultrafast Optical Microscopy (Minah Seo, Jinkyoung Yoo, Shadi Dayeh, Samuel Picraux, Antoinette Taylor and Rohit Prasankumar) Ultrafast Dynamics and Control in Transition Metal Oxides (Richard Averitt) Ultrafast Charge Dynamics in Ionic Materials Studied by Femtosecond X-Ray Diffraction (Thomas Elsaesser) Ultrafast Dynamics at Photovoltaic Interfaces (Guglielmo Lanzani) Carbon - Based Materials/Graphene: Ultrafast Photodynamics in Graphene: One-Photon Absorption Saturation vs Two-Photon Absorption (Wei Ji) Ultrafast Electron - Electron Dynamics in Graphene (Daniele Brida, Cristian Manzoni, Giulio Cerullo, Andrea Tomadin, Marco Polini, Rahul R Nair, Andre K Geim, Konstantin S Novoselov, Silvia Milana, Antonio Lombardo and Andrea Ferrari).

Singlet fission in organic crystals

Abstract: Singlet fission attracts an extensive attention in recent years due to its potential to improve the efficiency of organic solar cells. Ultrafast time-resolved measurements provide a powerful tool for direct determination of singlet fission pathways and rates. In this chapter we present and discuss the experimental data on oneand two-photon, as well as consecutive two-quantum induced singlet fission in organic crystals rubrene and perylene. Temperature and excitation wavelength dependent rates of the singlet fission are discussed in terms of the activation energy. Ultrafast singlet fission was demonstrated to proceed directly from upper vibrational states of S1, from upper excited states SN, bypassing relaxed S1 state, as well as from two-photon excited states.