Showing papers on "Photoexcitation published in 2002"
TL;DR: The calculations indicate a two-step mechanism for intrachain energy transfer with hopping along the conjugated chains as the rate-limiting step; the higher efficiency of the interchain transfer process is mainly due to larger electronic coupling matrix elements between closely lying chains.
Abstract: The energy-transfer processes taking place in conjugated polymers are investigated by means of ultrafast spectroscopy and correlated quantum-chemical calculations applied to polyindenofluorenes end-capped with a perylene derivative. Comparison between the time-integrated luminescence and transient absorption spectra measured in solution and in films allows disentangling of the contributions arising from intrachain and from interchain energy-migration phenomena. Intrachain processes dominate in solution where photoexcitation of the polyindenofluorene units induces a rather slow energy transfer to the perylene end moieties. In films, close contacts between chains favors interchain transport of the excited singlet species (from the conjugated bridge of one chain to the perylene unit of a neighboring one); this process is characterized by a 1-order-of-magnitude increase in transfer rate with respect to solution. This description is supported fully by the results of quantum-chemical calculations that go beyond the usual point-dipole model approximation and account for geometric relaxation phenomena in the excited state before energy migration. The calculations indicate a two-step mechanism for intrachain energy transfer with hopping along the conjugated chains as the rate-limiting step; the higher efficiency of the interchain transfer process is mainly due to larger electronic coupling matrix elements between closely lying chains.
343 citations
TL;DR: This analysis shows self-trapping of excitations on about six repeat units in the course of photoexcitation relaxation, identifies specific slow and fast nuclear motions strongly coupled to the electronic degrees of freedom, and predicts spectroscopic signatures of molecular conformations.
Abstract: Time-dependent photoexcitation and optical spectroscopy of $\ensuremath{\pi}$-conjugated molecules is described using a new method for the simulation of excited state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. Applications are made to poly(p-phenylene vinylene) oligomers. Our analysis shows self-trapping of excitations on about six repeat units in the course of photoexcitation relaxation, identifies specific slow (torsion) and fast (bond-stretch) nuclear motions strongly coupled to the electronic degrees of freedom, and predicts spectroscopic signatures of molecular conformations.
332 citations
TL;DR: In this article, a three-dimensional semiclassical Monte Carlo model is presented to describe fast carrier dynamics in semiconductors after photoexcitation, and the authors show that a magnetic field enhances THz emission by rotating the emitting dipole with respect to the sample surface, leading to an increased coupling of radiation through the surface.
Abstract: A three-dimensional semiclassical Monte Carlo model is presented to describe fast carrier dynamics in semiconductors after photoexcitation. Far-field terahertz (THz) radiation patterns are calculated for both InAs and GaAs with, and without, application of external magnetic fields. This analysis distinguishes between surface depletion field and photo-Dember mechanisms for generating THz radiation. The theoretical model reproduces experimental data from GaAs and InAs, and demonstrates that a magnetic field enhances THz emission by rotating the emitting dipole with respect to the sample surface, leading to an increased coupling of radiation through the surface.
310 citations
TL;DR: Direct vibrational-spectroscopic evidence for the isomerization taking place within 0.5 picosecond is presented, as has been suggested by previous optical femtosecond time-resolved experiments but questioned recently by picose Cond time-Resolved vibrational spectroscopy experiments.
Abstract: The vibrational dynamics of the retinal chromophore all-trans–to–13-cis photoisomerization in bacteriorhodopsin has been studied with mid-infrared absorption spectroscopy at high time resolution (about 200 femtoseconds). After photoexcitation of light-adapted bacteriorhodopsin, the transient infrared absorption was probed in a broad spectral region, including vibrations with dominant C–C, C=C, and C=NH stretching mode amplitude. All photoproduct modes, especially those around 1190 reciprocal-centimeters that are indicative for a 13-cis configuration of the chromophore, rise with a time constant of ∼0.5 picosecond. The results presented give direct vibrational-spectroscopic evidence for the isomerization taking place within 0.5 picosecond, as has been suggested by previous optical femtosecond time-resolved experiments but questioned recently by picosecond time-resolved vibrational spectroscopy experiments.
222 citations
TL;DR: Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials.
Abstract: The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso−meso, β−β, β−β positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, ∼500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of ∼1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from ∼4.5 ps for the T2 dimer to ∼0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes ...
200 citations
TL;DR: The time-resolved reflectivity in the intensely photoexcited Bi film is modulated by the coherent A(1g) phonon oscillation with a time-dependent oscillation period, which is attributed to an anharmonicity of the lattice potential.
Abstract: We have investigated the dynamical properties of the coherent anharmonic phonons generated in Bi under high density excitation. The time-resolved reflectivity in the intensely photoexcited Bi film is modulated by the coherent A(1g) phonon oscillation with a time-dependent oscillation period. As the pump power density is increased, the line shape of the A(1g) mode in the Fourier transformed spectra becomes asymmetric, and the redshift of the phonon frequency is observed. Analysis of the transient redshift with a wavelet transform reveals that the frequency of the A(1g) mode depends on the squared amplitude of the oscillation, which is attributed to an anharmonicity of the lattice potential.
191 citations
29 Jan 2002
TL;DR: In this paper, the authors describe the dynamics of photo-induced charge transfer and charge storage behavior in the dark in the context of Semiconductor-electrolyte interfaces.
Abstract: The sections in this article are
Introduction and Scope
Electron Energy Levels in Semiconductors and Energy Band Model
The Semiconductor–Electrolyte Interface at Equilibrium
The Equilibration Process
The Depletion Layer
Mapping of the Semiconductor Band-edge Positions Relative to Solution Redox Levels
Surface States and Other Complications
Charge Transfer Processes in the Dark
Current-potential Behavior
Dark Processes Mediated by Surface States or by Space Charge Layer Recombination
Rate-limiting Steps in Charge Transfer Processes in the Dark
Light Absorption by the Semiconductor Electrode and Carrier Collection
Light Absorption and Carrier Generation
Carrier Collection
Photocurrent-potential Behavior
Dynamics of Photoinduced Charge Transfer
Hot Carrier Transfer
Multielectron Photoprocesses
Nanocrystalline Semiconductor Films and Size Quantization
Introductory Remarks
The Nanocrystalline Film–Electrolyte Interface and Charge Storage Behavior in the Dark
Photoexcitation and Carrier Collection: Steady State Behavior
Photoexcitation and Carrier Collection: Dynamic Behavior
Size Quantization
Chemically Modified Semiconductor–Electrolyte Interfaces
Single Crystals
Nanocrystalline Semiconductor Films and Composites
Types of Photoelectrochemical Devices
Conclusion
Acknowledgments
165 citations
TL;DR: In this article, transient absorption data recorded over a range of wavelengths are analyzed to determine the amplitude of the breathing motion for 24.2 nm radius Au particles, where the expansion coordinate is treated as a damped harmonic oscillator and the driving force is thermal expansion due to lattice heating.
Abstract: Ultrafast laser excitation of metal particles coherently excites the symmetric breathing mode. This changes the electron density in the particle, which produces a periodic redshift in the position of the plasmon band. In this paper transient absorption data recorded over a range of wavelengths are analyzed to determine the amplitude of the breathing motion for 24.2 nm radius Au particles. The results are compared to a model calculation where the expansion coordinate is treated as a damped harmonic oscillator and the driving force is thermal expansion due to lattice heating (the temperature rise is determined from the energy absorbed by the sample). The only adjustable parameters in these calculations are the dephasing time of the oscillations and the time scale for energy transfer to the solvent. The experimental and calculated vibrational amplitudes are in excellent agreement, which shows that all the absorbed energy goes into expansion. However, the phases of the calculated and experimental traces do not match. The calculations can be brought into almost perfect agreement with the experimental results by including hot-electron pressure effects in the coefficient for thermal expansion of the particles. This contribution is significant in our experiments because laser excitation initially creates a very high electronic temperature. A simple expression for the time dependence of the transient absorption signal is also derived that explicitly accounts for sample polydispersity. In this expression the beat period is related to the mean radius, and the damping time to the mean radius and the width of the size distribution. Thus, time-resolved laser experiments can be used to obtain accurate information about the size distribution of metal particle samples.
165 citations
TL;DR: In this paper, the authors demonstrate the unique potential and the versatility of the PEEM approach, and review the current status with a certain emphasis on experiments with soft x-ray excitation.
Abstract: The imaging of surfaces by means of photoexcitation electron emission microscopy (PEEM) has recently received considerable interest. This is mainly due to the extended use and availability of brilliant synchrotron radiation in the soft x-ray regime which generally facilitates studies with surface specificity and chemical selectivity. The most popular application of the x-ray PEEM (XPEEM) technique concerns studies of magnetic systems and phenomena. By exploiting the high degree of circular or linear polarization of the synchrotron light, the magnetic microstructure in both ferromagnets and antiferromagnets can be visualized. In this contribution we demonstrate the unique potential and the versatility of the PEEM approach, and review the current status with a certain emphasis on experiments with soft x-ray excitation. In some cases, the high-energy excitation studies can be complemented by laboratory experiments employing threshold photoemission with ultraviolet light (UV-PEEM). Current limitations and future developments and perspectives of the PEEM technique applied to magnetic systems are discussed.
138 citations
TL;DR: Through transient absorption spectroscopy, it is shown that photoexcitation of the plasmon in Ag nanoparticles leads to exciton dynamics that differ strongly from J-aggregates alone or for J- Aggregates monolayers on bulk metal surfaces.
Abstract: The photochemistry of cyanine J-aggregates on the surface of colloidal Ag nanoparticles is reported. The photochemistry is initiated through ultrafast photoexcitation of the plasmon band in Ag nanoparticles, producing an enhanced near-field that interacts with the J-aggregate monolayer. Through transient absorption spectroscopy, we show that photoexcitation of the plasmon in Ag nanoparticles leads to exciton dynamics that differ strongly from J-aggregates alone or for J-aggregate monolayers on bulk metal surfaces. Specifically, charge-separated states with a lifetime of ∼300 ps between the J-aggregate and Ag colloid are formed. The reduction of the Ag nanoparticles is shown to be a multielectron process.
122 citations
TL;DR: In this article, a zinc phthalocyanine (ZnPc)/fullerene ligand (L) ensembles are assembled following simple biomimetic principles, which upon photoexcitation give rise to intra complex electron transfer quenching of the 1*Zn Pc fluorescence.
TL;DR: In this paper, the authors measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump--terahertz probe techniques, and the single crystal samples were excited using 800 nm, 100 fs pulses.
Abstract: We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump--terahertz probe techniques. The single crystal samples were excited using 800 nm, 100 fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300 K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4 ps, a power-law decay is observed consistent with dispersive transport.
TL;DR: In this article, the ground and excited state of 2-naphthol and some of its cyano derivatives in the gas phase was investigated. But the results were only semi-empirical.
Abstract: We present semiempirical AM1 calculations for the ground and excited state of 2-naphthol and some of its cyano derivatives in the gas phase. Following photoexcitation, the Mulliken electron density...
TL;DR: In this paper, photoisomerization dynamics and the electronic relaxation process of trans-azobenzene after the S 2ππ*) ← S 0 photoexcitation were investigated in solution by femtosecond and picosecond time-resolve.
Abstract: Photoisomerization dynamics and the electronic relaxation process of trans-azobenzene after the S2(ππ*) ← S0 photoexcitation were investigated in solution by femtosecond and picosecond time-resolve...
TL;DR: In this article, a bacteriochlorin-C60 dyad and a zinc chlorin dyad with the same short spacer have been synthesized and the rate constants for the charge-separation (CS) processes in these dyads were determined by fluorescence lifetime measurements of the dyads.
Abstract: A bacteriochlorin-C60 dyad (H2BCh-C60) and a zinc chlorin dyad (ZnCh-C60) with the same short spacer have been synthesized. The rate constants for the charge-separation (CS) processes in these dyads were determined by fluorescence lifetime measurements of the dyads. The charge-recombination (CR) rate constants of the dyads were determined using laser flash photolysis. The photoexcitation of the zinc chlorin-C60 dyad results in formation of the long-lived radical ion pair, which has absorption maxima at 790 and 1000 nm due to the zinc chlorin radical cation and the C60 radical anion, respectively. Photoexcitation of the free-base bacteriochlorin-C60 dyad with the same short linkage leads to formation of the radical ion pair, which decays quickly to the triplet excited state of the bacteriochlorin moiety. The driving force dependence of the electron-transfer rate constants of these dyads with a short spacer affords a small reorganization energy (λ = 0.51 eV) as compared with the λ value (0.66 eV) of zinc po...
TL;DR: In this article, the time evolution of the electric field in the surface layer of p-GaAs(100) was probed with 70 eV femtosecond EUV pulses by measuring the kinetic energy shifts of Ga-3d core-level photoelectrons after excitation with 3.1 eV Femtoscond laser pulses, while a subsequent relaxation was determined to evolve on a time scale of a few tens of picoseconds.
Abstract: Visible-pump/extreme ultraviolet (EUV)-probe spectroscopy using spectrally selected high harmonics of intense laser pulses is utilised for tracking the charge carrier dynamics on semiconductor surfaces. The time evolution of the electric field in the surface layer of p-GaAs(100) is probed with 70 eV femtosecond EUV pulses by measuring the kinetic-energy shifts of Ga-3d core-level photoelectrons after excitation with 3.1 eV femtosecond laser pulses. The observed transient changes of the surface photovoltage reveal carrier transport from the bulk to the surface to occur within 500 fs after photoexcitation, while a subsequent relaxation is determined to evolve on a time scale of a few tens of picoseconds.
TL;DR: Photophysical measurements reveal energy transfer events following the initial photoexcitation of the subphthalocyanine chromophore.
TL;DR: In this paper, the authors reported the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1.8-dinitro BIPS and its 1.2-carboxyethyl substituted derivative.
Abstract: We report the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1‘,3‘,3‘-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (6,8-dinitro BIPS) and its 1‘-(2-carboxyethyl) substituted derivative. The reaction is fast and essentially over in a few hundred picoseconds. The rate of MC-S1 state decay evaluated from transient absorbance can be correlated directly with the MC-S1 state lifetime as determined using stimulated and ordinary emission measurements. The recovery of the MC-S0 state from MC-S1 has a component with a lifetime of 60−78 ps in acetonitrile with a second component of 350−470 ps probably due to a metastable intermediate. We can further establish that the excited MC-S1 state takes on the order of 500 fs to form from higher-energy states after photoexcitation with 390 nm light.
TL;DR: Fluorescence excitation and dispersed emission methods in a supersonic jet are used to investigate the nature of the electronic excited states involved in the initial photoexcitation and subsequent photoisomerization of trans-CA and collected CA from the molecular beam after laser excitation in each of the three regions as further evidence of the photoisomeization process.
Abstract: The photoisomerization of trans-p-coumaric acid (trans-CA) triggers a photocycle in photoactive yellow protein that ultimately mediates a phototactic response to blue light in certain purple bacteria. We have used fluorescence excitation and dispersed emission methods in a supersonic jet to investigate the nature of the electronic excited states involved in the initial photoexcitation and subsequent photoisomerization of trans-CA. We observed three distinct regions in the fluorescence excitation spectrum of trans-CA. Region I is characterized by sharp features that upon excitation exhibit trans-CA S(1) emission. In region II, features increase in width and decrease in intensity with increasing excitation energy. Upon excitation, we observed dual emission from the S(1) state of trans-CA and what may be the S(1) state of cis-CA. The onset of dual emission corresponds to an isomerization barrier of about 3.4 kcal/mol. Finally, the extremely broad absorption feature in region III is excitation to the S(2) electronic excited state and excitation results in trans-CA S(1) emission. Furthermore, we collected CA from the molecular beam after laser excitation in each of the three regions as further evidence of the photoisomerization process. The relative amounts of trans- and cis-CA in the collected molecules were measured with high-pressure liquid chromatography. Although trans-CA was excited in all three regions, a significant cis-CA peak appeared only in region II, though a small cis peak was observed in region III.
TL;DR: In this paper, nonequilibrium vibrational excitations of para-nitroaniline (PNA) occurring after internal conversion from the photoexcited charge transfer state are studied by picosecond anti-Stokes Raman scattering.
Abstract: Nonequilibrium vibrational excitations of para-nitroaniline (PNA, 4-nitroaniline) occurring after internal conversion from the photoexcited charge transfer state are studied by picosecond anti-Stokes Raman scattering. Vibrational excess populations with distinctly different picosecond rise and decay times are found for a number of modes with frequencies between 860 and 1510 cm−1, including the overtone of a non-Raman active mode. A nonthermal distribution of vibrational populations exists up to about 6 ps after photoexcitation. The time-resolved experiments are complemented by steady-state infrared and Raman measurements as well as calculations based on density functional theory, providing a detailed analysis of the steady-state vibrational spectra of PNA and two of its isotopomers. A weakly Raman active vibration at about 1510 cm−1 displays the fastest rise time and a pronounced excess population and—thus—represents the main accepting mode. We suggest that an out-of-plane mode giving rise to the overtone...
TL;DR: In this article, it was shown that modulated near-infrared radiation can generate terahertz plasma oscillations in the channel of a high-electron mobility transistor.
Abstract: We show that modulated near-infrared radiation can generate terahertz plasma oscillations in the channel of a high-electron mobility transistor. This effect is associated with a temporarily periodic injection of the electrons photoexcited by modulated near-infrared radiation into the transistor channel. The excitation of the plasma oscillations has the resonant character. It results in the pertinent excitation of the electric current in the external circuit that can be used for generation of terahertz electromagnetic radiation.
TL;DR: In this article, the exact quantum yields for primary H atom formation were measured under collision-free conditions for the room-temperature gas-phase dissociation of acetylene (C2H2) after photoexcitation at 193.3 nm and at the H-atom Lyman-a wavelength (121.6 nm) by a pulsed laser photolysis (LP)-laser-induced fluorescence (LIF) ‘pump-and-probe’ technique.
TL;DR: In this article, photoexcitation-electron-paramagnetic-resonance (photo-EPR) studies were performed on p-type 4H-SiC irradiated with 2.5 MeV electrons.
Abstract: Photoexcitation-electron-paramagnetic-resonance (photo-EPR) studies were performed on p-type 4H-SiC irradiated with 2.5 MeV electrons. At W-band frequencies (∼95 GHz) different EPR spectra could be well separated, allowing a reliable determination of the ground state levels of the associated defects. The photo-EPR results obtained for the positively charged carbon vacancy (VC+) can be explained by a deep donor model with the (+/0) level located at (1.47±0.06) eV above the valence band.
TL;DR: In this article, the femtosecond transient photoluminescence (PL) and quasi-steady-state photo-induced absorption spectroscopy were investigated on the organic semiconductor poly-6, 6', 12, 12, 14, 12'-tetraalkyl-2, 8-indenofluorene (PIF).
Abstract: We present combined results of femtosecond transient photoluminescence (PL), femtosecond transient absorption and quasi-steady-state photoinduced absorption spectroscopy on the organic semiconductor poly-6, 6', 12, 12'-tetraalkyl-2, 8-indenofluorene (PIF). By control of interchain order via the choice of the side-chain substituents, we have investigated its effect on exciton and polaron dynamics in this model electronic material. We show that interfaces between ordered and disordered domains play a significant role in the photophysics. At high photoexcitation fluence, a high yield (~10%) of polarons is only observed in the ordered semiconductor. This process arises from two-step photoexcitation, first to the lowest exciton, and then to a high-energy state of opposite symmetry. In contrast, triplet exciton population is generated via sequential excitation with smaller yield (< 1 %) in both ordered and disordered materials. In the low fluence regime, triplet excitons are found to arise from evolution of polarons generated with low efficiency (also < 1 %) by diffusion-limited processes. The triplet generation yield is strongly dependent on order, with the disordered material displaying a higher yield. Polaron decay is found to be thermally activated, with a higher activation energy and lower room-temperature recombination rate in the ordered material. Furthermore, we do not find that emissive keto defects play a defining role in the PL properties of our PIF samples. Instead, absorption features of aggregate-like species, which we believe to lead to sub-gap emission, are evident in the photocurrent action spectrum of the more ordered PIF derivative.
TL;DR: By applying photoexcitation by ultrashort laser pulses to single crystal thin CrO(2) films to trigger coherent transient magnetization rotation on a subnanosecond time scale, the transient precession of the magnetization can be phase controlled, depending on the time separation between the pulses.
Abstract: We have applied photoexcitation by ultrashort laser pulses to single crystal thin CrO 2 films to trigger coherent transient magnetization rotation on a subnanosecond time scale, in macroscale single domains. Moreover, by applying the photoexcitation by pairs of temporally separated pump pulses, the transient precession of the magnetization can be phase controlled, depending on the time separation between the pulses. The mechanism behind the photoexcitation originates from the modulation of the magnetocrystalline anisotropy by nonthermal hot electron spins.
TL;DR: In this paper, the effect of sample morphology on ultrafast dynamics of photoexcited species in poly(9,9-dioctyl)fluorene (PFO) was studied.
TL;DR: In this article, the free electron laser FELIX was used to excite neutral phosphorus and bismuth donors embedded in bulk monocrystalline silicon, and the influence of nonequilibrium intervalley TO phonons on the population of excited Bi impurity states was discussed.
Abstract: Frequency-tunable radiation from the free electron laser FELIX was used to excite neutral phosphorus and bismuth donors embedded in bulk monocrystalline silicon. Lasing at terahertz frequencies has been observed at liquid helium temperature while resonant pumping of odd parity impurity states. The threshold was about two orders of magnitude below the value for photoionization pumping. The influence of nonequilibrium intervalley TO phonons on the population of excited Bi impurity states is discussed.
TL;DR: In this paper, an ab initio embedded cluster study of the ground and excited states for the rutile (1 1 0) surface with adsorbed water molecule is presented.
TL;DR: The photophysical and photochromic properties of 2,2-diphenyl-2H-naphtho[1, 2-b]pyran and substituted derivatives were investigated by steady state and time-resolved optical absorption and emission spectroscopy in solution at room temperature and in a frozen matrix at 77 K as discussed by the authors.
Abstract: The photophysical and photochromic properties of 2,2-diphenyl-2H-naphtho[1,2-b]pyran and substituted derivatives were investigated by steady state and time-resolved optical absorption and emission spectroscopy in solution at room temperature and in a frozen matrix at 77 K. Fluorescence quantum yields, fluorescence lifetimes, and singlet energies depend strongly on the substitution patterns. Photoexcitation of the naphthopyrans (A) leads to efficient ring opening to produce the merocyanines (B) and (C). The optical absorption of the merocyanines can be tuned by the substituents and can cover most of the visible spectrum (400−700 nm). The decoloration kinetics of the open forms (merocyanines) B and C to produce naphthopyrans (A) depends strongly on the substituents. The ring closure rate constants (kB→A) range from 0.0009 to 0.04 s-1.
TL;DR: Trans-polyacetylene with a degenerate ground state has a nonlinear excitation of soliton after photoexcitation, due to the electron-phonon coupling, which induces a breather oscillation characterized by collective stretching vibration of the carbon-carbon bonds.
Abstract: Trans-polyacetylene with a degenerate ground state has a nonlinear excitation of soliton after photoexcitation, due to the electron-phonon coupling. The excess energy of an excited electron-hole pair over a soliton pair creation induces a breather oscillation characterized by collective stretching vibration of the carbon-carbon bonds. A time-frequency analysis of pump probe signal shows that instantaneous frequencies of stretching modes are modulated for approximately 50 fs after excitation and the modulation period is 44+/-3 fs consistent with the theoretical expectation, clearly verifying the breather.