@article {1658, title = {Observation of Photoinduced Proton Transfer between the Titania Surface and Dye Molecule}, journal = {The Journal of Physical Chemistry C}, year = {2020}, author = {Nishikiori, H. and Kondo, H. and Kageshima, Y. and Hooshmand, N. and Panikkanvalappil, S. R. and Valverde-Ch{\'a}vez, D.A. and Silva, C. and El-Sayed, M.A. and Teshima,K.} } @article {1348, title = {Surface Assembly and Plasmonic Properties in Strongly Coupled Segmented Gold Nanorods}, journal = {Small}, year = {2013}, note = {MEDLINE AN 2013463112(Journal; Article; (JOURNAL ARTICLE))}, month = {//}, abstract = {An assembly strategy is reported such that segmented nanorods fabricated through template-assisted methods can be robustly transferred and tethered to a pre-functionalized substrate with excellent uniformity over large surface areas. After embedding the rods, sacrificial nickel segments were selectively etched leaving behind strongly coupled segmented gold nanorods with gaps between rods below 40 nm and as small as 2 nm. Hyper-spectral imaging is utilized to measure Rayleigh scattering spectra from individual and coupled nanorod elements in contrast to common bulk measurements. This approach discerns the effects of not only changing segment and gap size but also the presence of characteristic defects on the plasmonic coupling between closely spaced nanorods. Polarized hyper-spectral measurements are conducted to provide direct observation of the anisotropic plasmonic resonance modes in individual and coupled nanorods, which are close to those predicted by computer simulations for nanorods with ideal shapes. Some common deviations from ideal shape such as non-flat facets and asymmetric tails are demonstrated to result in the appearance of characteristic plasmon resonances, which have not been considered before. The large-scale assembly of coupled noble nanostructures with fine control over geometry and high uniformity provides means to strongly tune the scattering, absorption, and near-field plasmonic properties through the geometric arrangement of precisely controlled nanorod segments.[on SciFinder (R)]}, isbn = {1613-6829}, author = {Gupta, Maneesh K. and Konig, Tobias and Near, Rachel and Nepal, Dhriti and Drummy, Lawrence F. and Biswas, Sushmita and Naik, Swati and Vaia, Richard A. and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.} } @article {1111, title = {Effect of Orientation on Plasmonic Coupling between Gold Nanorods}, journal = {Acs Nano}, volume = {3}, number = {11}, year = {2009}, note = {Tabor, Christopher Van Haute, Desiree El-Sayed, Mostafa A.}, month = {Nov}, pages = {3670-3678}, abstract = {Radiative coupling of induced plasmonic fields in metal nanoparticles has drawn increasing attention in the recent literature due to a combination of improved experimental methods to study such phenomena and numerous potential applications, such as plasmonic nanoparticle rulers and plasmonic circuitry. Many groups, including ours, have used a near-exponential fit to express the size scaling of plasmonic coupling. First, we show experimental agreement between previously simulated nanorod coupling and plasmonic coupling in electron beam lithography (EBL) fabricated nanorods using the near-exponential expression. Next, we study the effect of nanoparticle orientation on plasmonic coupling using EBL and DDA simulations. We develop a mathematical relationship that is consistent with our findings and quantitatively describes plasmonic coupling between nanorods as a function of orientation, separation, induced dipole strength, and the dielectric constant of the medium. For applications utilizing plasmonic coupling to become viable with particle shapes that do not have spherical symmetry, such as nanoprisms and nanorods, comparison of the experimental and theoretical results of how particle orientation affects plasmonic coupling is essential.}, isbn = {1936-0851}, doi = {10.1021/nn900779f}, author = {Tabor, C. E. and Van Haute, D. and El-Sayed, Mostafa A} } @article {1132, title = {Time-resolved investigation of the acoustic vibration of a single gold nanoprism pair}, journal = {Journal of Physical Chemistry C}, volume = {112}, number = {30}, year = {2008}, note = {Burgin, J. Langot, P. Del Fatti, N. Vallee, F. Huang, W. El-Sayed, M. A.}, month = {Jul}, pages = {11231-11235}, abstract = {The acoustic vibration of single gold nanoprism pairs on a glass substrate has been investigated in the time-domain combining a spatial modulation spectroscopy microscope with a high-sensitivity femtosecond pump-probe setup. Three modes were observed and ascribed to two in-plane and one out-of-plane vibration of the nanoprisms forming the pair, in agreement with a theoretical analysis. The periods of the two former modes with similar nature show weak (about 10\%) and well correlated pair to pair fluctuations that can be unambiguously ascribed to variation of the prism geometry. In contrast, strong fluctuations, by almost a factor of 6, of the mode damping are evidenced with no correlation with their period. This indicates large variations of the prism-substrate coupling, providing a unique way for its local investigation.}, isbn = {1932-7447}, doi = {10.1021/jp802365s}, author = {Burgin, J. and Langot, P. and Del Fatti, N. and Vallee, F. and Huang, Wenyu and El-Sayed, Mostafa A} } @article {1161, title = {Femtosecond excitation dynamics in gold nanospheres and nanorods}, journal = {Physical Review B}, volume = {72}, number = {23}, year = {2005}, note = {Varnavski, OP Goodson, T Mohamed, MB El-Sayed, MA}, month = {Dec}, abstract = {Femtosecond visible photoluminescence is detected from gold nanoparticles using time-resolved fluorescence upconversion spectroscopy. We directly compared this fast luminescence from gold nanospheres (subset of 25 nm) with that obtained from nanorods (subset of 15x40 nm, subset of 15x27 nm) under vis (3.02 eV) and UV(4.65 eV) excitation. A fast (similar to 50 fs) decay was obtained for the nanoparticles and the emission was depolarized. Degenerate femtosecond pump-probe experiments in the low excitation intensity regime demonstrated much slower electron thermalization and/or equilibration dynamics on the time scale of a few hundred femtoseconds. These features strongly indicate a d-hole-conduction electron recombination process as the origin of this photoluminescence. A direct comparison of the fast emission spectra from nanorods and nanospheres is used to discuss the emission enhancement mechanism. These results suggest that the classical local field enhancement theory describes quantitatively well many of the emission features of nanorods with respect to those for nanospheres without invoking more complex models.}, isbn = {1098-0121}, doi = {10.1103/PhysRevB.72.235405}, author = {Varnavski, O. P. and Goodson, T. and Mohamed, MB and El-Sayed, Mostafa A} } @article {845, title = {Relative enhancement of ultrafast emission in gold nanorods}, journal = {The Journal of Physical Chemistry B}, volume = {107}, year = {2003}, pages = {3101-3104}, publisher = {ACS Publications}, abstract = {Time-resolved fluorescence spectroscopy has been employed to probe the ultrafast emission observed in gold nanospheres and nanorods. The decay of the emission was found to be <=50 fs. The ultrafast emission from nanorods has been directly compared to that for nanospheres and the dispersion of the relative local field enhancement factor was obtained and compared with calculations. Measurements with both visible and ultraviolet excitations have been analyzed. These results give the first observation and analysis of the mechanism for the local field-enhanced ultrafast emission in gold nanorods and nanospheres.}, isbn = {1520-6106}, doi = {10.1021/jp0341265}, url = {http://dx.doi.org/10.1021/jp0341265}, author = {Varnavski, O. P. and Mohamed, MB and El-Sayed, Mostafa A and Goodson III, T.} } @article {1211, title = {The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {98}, number = {15}, year = {2001}, note = {Logunov, SL Volkov, VV Braun, M El-Sayed, MA}, month = {Jul}, pages = {8475-8479}, abstract = {We present the results of two-pump and probe femtosecond experiments designed to follow the relaxation dynamics of the lowest excited state (S-1) populated by different modes. In the first mode, a direct (S-0 --> S-1) radiative excitation of the ground state is used. In the second mode, an indirect excitation is used where the S-1 state is populated by the use of two femtosecond laser pulses with different colors and delay times between them. The first pulse excites the S-0 --> S-1 transition whereas the second pulse excites the S-1 --> S-n transition. The nonradiative relaxation from the S-n state populates the lowest excited state. Our results suggest that the S1 state relaxes faster when populated nonradiatively from the S-n state than when pumped directly by the S-0 --> S-1 excitation. Additionally, the S-n --> S-1 nonradiative relaxation time is found to change by varying the delay time between the two pump pulses. The observed dependence of the lowest excited state population as well as its dependence on the delay between the two pump pulses are found to fit a kinetic model in which the S-n state populates a different surface (called Si) than the one being directly excited (S-1). The possible involvement of the A(g) type states, the J intermediate, and the conical intersection leading to the S-0 or to the isomerization product (K intermediate) are discussed in the framework of the proposed model.}, isbn = {0027-8424}, doi = {10.1073/pnas.141220198}, author = {Logunov, Stephan L. and Volkov, V. V. and Braun, Markus and El-Sayed, Mostafa A} } @article {1224, title = {The {\textquoteright}lightning{\textquoteright} gold nanorods: fluorescence enhancement of over a million compared to the gold metal}, journal = {Chemical Physics Letters}, volume = {317}, number = {6}, year = {2000}, note = {Mohamed, MB Volkov, V Link, S El-Sayed, MA}, month = {Feb}, pages = {517-523}, abstract = {Gold nanorods capped with micelles and having an aspect ratio of 2.0-5.4 are found to fluoresce with a quantum yield which is over a million times that of the metal. For rods of the same width, the yield is found to increase quadratically while the wavelength maximum increases linearly with the length. We assign this emission to the electron and hole interband recombination. The increase in the emission yield results from the enhancement effect of the incoming and outgoing electric fields via coupling to the surface plasmon resonance in the rods. This is similar to the previously proposed fluorescence and the Raman enhancement on noble metal rough surfaces. (C) 2000 Published by Elsevier Science B.V. All rights reserved.}, isbn = {0009-2614}, doi = {10.1016/s0009-2614(99)01414-1}, author = {Mohamed, MB and Volkov, V. V. and Link, Stephan and El-Sayed, Mostafa A} } @article {864, title = {Optical rotation of the second harmonic radiation from retinal in bacteriorhodopsin monomers in Langmuir-Blodgett film: evidence for nonplanar retinal structure.}, journal = {Biophysical journal}, volume = {73}, year = {1997}, month = {1997 Dec}, pages = {3164-70}, abstract = {We observed optical rotation of the plane of polarization of the second harmonic (SH) radiation at 532 nm (in resonance with the retinal absorption) generated in reflection geometry in Langmuir-Blodgett film of bacteriorhodopsin (bR). The analysis of the experimental data showed that this effect arises from the nonvanishing contribution of the antisymmetrical part of the hyperpolarizability tensor. This requires that the dipole moment of the resonant electronic transition, the change of the dipole moment upon electronic excitation, and the long axis of the retinal not be coplanar. Such conditions are satisfied only if the retinal has a nonplanar geometry, a conclusion that could lend support to the heterogeneity model of the origin of the biphasic band shape of the linear CD spectrum of the retinal in bR. On the basis of our theoretical analysis, we were able to estimate the angle between the induced dipole moment and the plan that contains the long axis of the chromophore and the transition dipole moment of the retinal absorption.}, keywords = {Bacteriorhodopsins, Biophysical Phenomena, Biophysics, Circular Dichroism, Molecular Structure, Optics and Photonics, Retinaldehyde, Spectrophotometry}, issn = {0006-3495}, doi = {10.1016/S0006-3495(97)78342-5}, author = {Volkov, V. V. and Svirko, Y P and Kamalov, Valey F. and Song, Li and El-Sayed, Mostafa A} }