Pohang University of Science and Technology · 化学
Professor Taiha Joo's research lab specializes in ultrafast nonlinear optical spectroscopy to investigate dynamic processes in complex molecular systems, particularly focusing on solvation dynamics, energy transfer, and electronic dephasing in biological and chemical environments. The lab employs advanced femtosecond time-resolved techniques—such as transient absorption, photon echoes, transient grating, and fifth-order nonlinear spectroscopy—to probe ultrafast electronic and vibrational dynamics with high temporal and spectral resolution. A central theme is understanding how molecular structure, solvent environments, and protein matrices influence energy transfer and reaction dynamics in light-harvesting systems and functional molecules.
Figures are computed from collected data and may differ slightly.
Several closely related third-order nonlinear time-resolved spectroscopic techniques, pump/probe transient absorption, transient grating, and three pulse stimulated photon echo peak shift measurements, are investigated theoretically and experimentally. It is shown in detail, through the consideration of response functions and numerical simulations including both finite pulse durations and detuning from exact resonance, how the solvation dynamics are manifested in these third-order nonlinear time
The underlying dynamics of the B800 absorption band in isolated LH2 of Rb. sphaeroides at room temperature is studied by transient absorption, transient grating, and photon echoes using 30 fs pulses. The energy transfer time from B800 to B850 is determined to be 800 fs, similar to the value reported previously. The three pulse stimulated photon echo identifies several important contributions to the B800 absorption line shape and thereby the dynamics of the system involved: several low frequency
An ultra-fast chemical reaction can act as an impulsive excitation of the vibrations. Excited state intramolecular proton transfer in 10-hydroxybenzo[h]quinoline proceeds in 13 fs. As a result, product vibrational modes with their periods longer than (13 x 2) fs are coherently excited in the product potential surface, which can be observed most unambiguously by the oscillations in the time-resolved fluorescence signal of the product keto isomer.
The electronic dephasing of two oxazine dyes dissolved in ethylene glycol at room temperature is investigated by femtosecond degenerate four wave mixing (DFWM) experiments. Both two-pulse and three-pulse DFWM with simultaneous detection of the signals at two distinct phase-matching directions permits detailed investigation of dephasing dynamics in a room temperature liquid. At least two stochastic processes are responsible for the observed electronic dephasing: one is treated empirically as an e
Reaction-based fluorescent probes for monoamine oxidases A and B are developed based on a new two-photon absorbing compound and its precursor. The probes show turn-on fluorescence response to the enzymes owing to the two-photon absorbing compound produced by the enzymatic activity, as monitored by one- as well as two-photon microscopy for the first time.
We report a new spectroscopic measurement based on fifth order nonlinear response from a molecule in a room temperature liquid. In conjunction with conventional three pulse stimulated photon echo, detailed information on solvent–solute dynamics for a wide range of time scales has been obtained. Both the ultrafast inertial components and much slower dynamics of the solvent are found to make important contributions to the solvent relaxation. The potential of the fifth order measurements is discuss
Femtosecond time-resolved coherent Stokes Raman spectroscopy (CSRS) signals of benzene-h6, benzene-d6, and their 1 : 1 binary mixture are investigated at room temperature with two different polarization geometries. The reorientational correlation time of benzene as well as the vibrational dephasing time of the v1 ring-breathing mode have been measured precisely. Bohr frequency difference beats have been resolved between the v1 modes of 12C6H6 and 12C6H6 and 12C513CH6 protonated benzenes and the
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