Electronic and Vibrational Coherence Dynamics in a Cyanine Dye Studied Using a Few‐Cycle Pulsed Laser

Abstract

We report the relaxation times of electronic and vibrational coherence in the cyanine dye 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2,2'-indotricarbocyanine, measured using a 7.1 fs pulsed laser. The vibrational phase relaxation times are found to be between 380 and 680 fs in the ground and lowest excited singlet states. The vibrational dephasing times of the 294, 446, and 736 cm(-1) modes are relatively long among the six modes associated with excited-state wave packets. The slower relaxations are explained in terms of a coupled triplet of vibrational modes, which preserves coherence by forming a tightly bound group to satisfy the condition of circa conservation of vibrational energy. Using data from the negative-time range (i.e., when the probe pulse precedes the pump pulse), the electronic phase relaxation time is found to be 31+/-1 fs. The dynamic vibrational mode in the excited state (1171 cm(-1)), detected in the positive-time range, is also studied from the negative-time traces under the same experimental conditions.

Real-Time Spectroscopy of Single-Walled Carbon Nanotubes for Negative Time Delays by Using a Few-Cycle Pulse Laser

“…The pump then “probes” the decay by perturbing the probe polarization, although no pump energy is absorbed by the sample medium, and the signal is detected in the direction of the probe beam. , The perturbed free-induction decay term, which occurs only in the negative time range, can be used to determine the electronic phase relaxation time and to study the vibrational phase relaxation dynamics in excited electronic states . Recently, we reported the experimental observation of absorbance changes for several molecular systems for negative time delays. , This negative-time measurement is a powerful method for studying coherent phonon vibration in excited states without the effect of wave packet motion in the ground states under the same experimental condition as the real population relaxation associated with vibrational dynamics, including both the ground state and excited state. In addition, knowledge of electronic dephasing dynamics is very important for elucidating the properties of excited states and the dynamics of optical nonlinear processes, which offer information on the response dynamics of various device applications such as optical switching and optical signal processing. , The time sequences of two fields of the pump and one from the probe are the same pulse ordering as that denoted by type S III configuration in the two-dimensional spectroscopy. , In this paper, we report what is to the best of our knowledge the first observation of the vibrational and electronic coherence dynamics of SWNTs in negative time delays using a pump–probe technique with an extremely short (7.1 fs) and broad bandwidth pulse in the visible spectrum and using an ultrahigh-sensitivity broadband detection system composed of a polychromator and a multichannel lock-in amplifier, which can detect 128 different wavelengths simultaneously.…”

Electronic relaxation and coherent phonon dynamics in semiconducting single-walled carbon nanotubes with several chiralities

“…Since the pump laser is resonant with several chiral species, we first separate the spectra associated with each of these species. For quantitative discussion, the phenomenological description of the probe photon energy dependence A(ω probe ) of the vibrational amplitude can be expressed as 66 A(ω probe = ω S ) = C 1S |a(ω probe ) − a(ω probe − ω v )|, (13) A(ω probe = ω AS ) = C 1AS |a(ω probe ) − a(ω probe + ω v )|, (14) a(ω probe ) = L(ω probe )(1 − 10 −Aω probe ).…”

“…They do not contribute to the first moment if an appropriate integration range is selected, because the Raman contributions are determined by the zeroth moment. 66 The time-dependent modulation of the difference absorption due to the MPM of each tube can be evaluated by performing a first-moment calculation on the corresponding absorption band in the A spectrum as a function of sampling time. Figure 11(a) graphs M 1 (t) time traces for four spectral components corresponding to the absorption associated with different chiralities.…”

“…This behavior was already observed in a one-dimensional system of J-aggregated molecules. 66 Accordingly, the spectral shift due to the refractive index modulation is so small that the index changes can be considered to be linear with respect to the probe spectral changes. Therefore, the MPM mechanism can be depicted in the classical way using Q(t), as shown in Fig.…”

Development of real-time vibrational spectroscopy of molecules in electronic excited states: toward mapping molecular potential energy hypersurfaces

“…Therefore, to fully utilize the available frequency information, a broadband detector is required that has both high resolution and high sensitivity. Our group previously reported an original detection system composed of a multichannel lock-in amplifier (MLA) [40] and we demonstrated the advantages of this system by applying it to several samples [16][17][18][19][20][21][22][23][24][25][26][27][28][29]40]. Recently, several groups have utilized two-dimensional (2D) detectors, such as CCDs [41] and photodiode arrays [42].…”