Abstract
Broadband real-time dynamic vibronic coupling in Chl-a were experimentally studied using few cycle laser pulses of 6.8fs duration and a 128-channnel lock-in amplifier. Thanks to the extreme temporal resolution benefitting from the ultrashort laser pulse, the real-time modulation of the electronic transition energy induced by the molecular vibrations were calculated by the time dependent first moments of the bleaching band. The transition energy was found to be modulated periodically with the same frequencies of molecular vibration found in the Fourier amplitude spectrum of the difference absorbance real-time traces. This was interpreted to be due to the difference in the effective transition energy associated with the wavepacket motion induced by the equilibrium positions of potential curves between the ground state and the excited state. Using the values, Huang-Rhys factors for several vibrational modes involved in the spectral modulation at the room-temperature have been determined.
Highlights
Chlorophyll a (Chl-a) plays an essential role in the energy transfer and charge separation in the photosynthetic unit, Chl-a and Chl-containing proteins have been extensively studied [1,2,3].Among these studies, applications of laser pulses with durations from several tens to 100fs have been reported
The vibrational structure of Chl-a has been obtained by resonance Raman spectroscopy, spectral hole-burning, and fluorescence line-narrowing techniques, respectively [3,4,5,6,7]
The vibrational information of its most interesting Qy-band is usually studied at very low temperature (~4K) due to the temperature requirement of these vibrational methods and disturbance by intense fluorescence in Chl-a solution
Summary
Chlorophyll a (Chl-a) plays an essential role in the energy transfer and charge separation in the photosynthetic unit, Chl-a and Chl-containing proteins have been extensively studied [1,2,3].Among these studies, applications of laser pulses with durations from several tens to 100fs have been reported. With the development of the ultrashort pulse laser techniques, few-cycle pulses in the visible and near-infrared ranges have been generated [8,9] Among these methods, the noncollinear phase-matched optical parametric amplification (NOPA) technique has attracted great interests. The noncollinear phase-matched optical parametric amplification (NOPA) technique has attracted great interests Using this method, sub-5-fs pulses in the visible spectral range have been generated by our group [8,9]. We used a 6.8 fs laser for broad-band pump-probe real-time vibrational spectroscopy to obtain both electronic relaxation and vibrational dynamics of Chla at physiologically relevant temperature. The modulations of the electronic transition energy have been observed and determined, and been explained in terms of Huang–Rhys factors
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