New photo-isomerization path of indocyanine green in condensed phase investigated by two-pump excitation

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

“…Thus most of the contribution of cis-form is buried in that of trans-form in Figure 1. At 870 nm, the contribution of cis-form is much larger than that of trans-form [7], but only the tail of the cis-contribution is observed around 870 nm and this tail is smaller than the peak of trans-form around 790 nm.…”

“…The molecules were excited by a single NIR femtosecond pulse (790 nm, 30 mJ/ cm 2 ) and changes were monitored by a white light continuum at the delay of 5 ns. A positive change around 790 nm and a negative change around 870 nm were observed, which were assigned to the photobleaching in the S 0 state in the trans configuration and the transient absorption by the cis-isomer produced in the photoisomerization, respectively [7]. The pump-probe delay time of 5 ns is longer than the timescale of the trans-cis photoisomerization (1-3 ns) [7] and much shorter than the lifetime of the cis isomer (430 ls) [16].…”

“…The procedures for two-pulse correlation measurement are basically the same as those reported previously [7]. Briefly, two ultrashort laser pulses were introduced as a 'pump pulse pair' for excitation and the transient absorption of a photo-isomer was measured as a function of the delay time between the two pump pulses by a much delayed probe pulse.…”

“…On the ground state potential, molecules either relax back to the trans configuration or form a cis isomer [8,9]. In our previous study, we irradiated two near-infrared (NIR) ultrashort pulses on indocyanine green (ICG), a widely used and investigated dye [10][11][12][13][14][15][16][17], and measured transient absorption by photo-produced cis-isomers as a function of pump-pump interval, in other words two-pulse correlation (2PC) trace [7]. We found that the transient absorption shows clear dependence on pumppump interval and increases with decrease of the interval.…”

“…Recently, we investigated a new photoisomerization path of cyanine dye, a model compound of photoreaction in the condensed phase, by two-pulse excitation [7]. The reaction dynamics involved in the conventional photoisomerization path of cyanine dye is understood as follows: upon photo-excitation of the dye in the thermodynamically stable trans configuration with a short laser pulse, a wavepacket is created on the potential energy surface of the excited singlet state (S 1 ).…”