Control of reaction efficiency by two-color two-pulse excitation: Photoisomerization of indocyanine green in condensed phase

Vibronic relaxation dynamics at intermediate state of two-pump excitation: Photoisomerization of indocyanine green in ethanol

“…The UV pump pulse was modulated by a mechanical chopper and the UV pump-induced transmission change of the probe pulse was measured with a lock-in amplifier. In contrast to our previous studies where both NIR and UV pump pulses were modulated simultaneously by the chopper, 25,26 in this study we were able to improve the S/N by chopping only the UV pump pulse. We briefly explain the principle in the following paragraph.…”

“…The procedures for 2PC measurement were largely the same as those reported previously. 25,26 Briefly, two ultrashort laser pulses were introduced as a 'pump pulse pair' for excitation, and the transient absorption of the photo-isomer was measured as a function of the delay time between the two pump pulses by a much-delayed probe pulse. In our measurements, the delay time between the two pump pulses was shorter than 5 ps, whereas the delay time of the probe pulse relative to the pump pulse pair was 2.5 ns.…”

“…[22][23][24] Recently, we investigated the multiphoton excitation process in the trans-to-cis photoisomerization of ICG molecules 20 by using a twopulse excitation, and we found relaxation processes with time constants of a sub-picosecond order. 25,26 However, we could not evaluate or assign the time constants due to the low signalto-noise ratio (S/N). Thus, we could not uncover the relaxation dynamics of the intermediate states of the multiphoton excitation process.…”

Cross-Term Selective, Two-Pulse Correlation Measurements by Phase-Shifted Parallel Modulation for Analysis of a Multi-Photon Process

“…In order to examine the origin of the negative background, asym-2PC measurements in which the pump-pulse energies were set to unequal values 6,7 were carried out. Figure 6 shows the results of asym-2PC measurements.…”

“…For understanding and controlling photochemical reaction, knowledge about reaction pathways through multi-photon excitation is important, 1,–5 even if one-photon excitation is accessible to the reaction pathways, 6,7 because multi-photon excitation is the gateway to the manifold of electronically excited states that have characteristic properties and can follow unique reaction pathways. In order to monitor the photo-induced reaction passing through the multi-photon process buried in that passing through a one-photon process, multiphoton selective method is necessary.…”