Probing with randomly interleaved pulse train bridges the gap between ultrafast pump-probe and nanosecond flash photolysis

Abstract

Despite the long-standing importance of transient absorption (TA) spectroscopy, many researchers remain frustrated by the difficulty of measuring the nanosecond range in a wide spectral range. To address this shortcoming, we propose a TA spectrophotometer in which there is no synchronization between a pump pulse and a train of multiple probe pulses from a picosecond supercontinuum light source, termed the randomly-interleaved-pulse-train (RIPT) method. For each pump pulse, many monochromatized probe pulses impinge upon the sample, and the associated pump-probe time delays are determined passively shot by shot with subnanosecond accuracy. By repeatedly pumping with automatically varying time delays, a TA temporal profile that covers a wide dynamic range from subnanosecond to milliseconds is simultaneously obtained. By scanning wavelength, this single, simple apparatus acquires not only wide time range TA profiles, but also broadband TA spectra from the visible through the near-infrared regions. Furthermore, we present a typical result to demonstrate how the RIPT method may be used to correct for fluorescence, which often pollutes TA curves.

Photoinduced Electron Transfer in 9‐Substituted 10‐Methylacridinium Ions

“…Subnanosecond laser-induced transient absorption spectra were collected by acustomized measuring system based on the recently proposed RIPT method by Nakagawa et al [28] The pump source is ap assively Q-switched microchip laser (PowerChip PNV-M02510, Teem Photonics, 1kHz, 350 ps, 355 nm, 25 mJ), and the probe source is as upercontinuum radiation source (SC-450, Fianium, 20 MHz, 50-100 ps, 450-2000 nm). The monochromatized probe pulses from ap redispersive monochromator (MD200, Unisoku), which were asynchronous with the pump pulse, impinged on the sample, and the beam transmitted through the sample and its reference beam were detected by InGaAs photodiodes (G10899-01K, 400-1600 nm, Hamamatsu).…”

“…Thus, the transient absorption spectrum in Figure 1b can be assigned to the singletE Tstate [ 1 (AcrC-1NAC + )].T he rate constant of formationo ft he singlet ET state (3.4 10 12 s À1 )a greesw ith the fluorescenced ecay rate constanto fA cr + -1NA (3.2 10 12 s À1 )i nF igure 1a.S uch agreement of the rate constant of formation of the singlet ET state with the fluorescenced ecay rate constant was also confirmed for Acr + -Mes in MeCN at 298 K( Figure S4 in the Supporting Information). [17] The time profile of the singlet ET state of Acr + -Mes was examined by subnanosecond laser-induced transient absorption measurements( see Experimental Section), [28] as shown in Figure 2. The decay of the absorption band at 500 nm was accompanied by appearance of an NIR absorption around 1000 nm.…”

Pyrrole‐Based π‐System–PtII Complexes: Chiroptical Properties and Excited‐State Dynamics with Microsecond Triplet Lifetimes

“…In ordert oe lucidate the lifetimes of the long-lived T 1 states of 2a,b,t ransient absorption measurements on the nanosecond to microsecond time scale in degassed CH 2 Cl 2 were conducted using the randomly interleaved pulse train (RIPT) method ( Figure 5c). [16] The transient absorption spectra of 2a,b on nanosecondt om icrosecond time scales are identicalt o those measured on the sub-picosecond to nanosecond time scale. The transienta bsorption dynamics was fitted with the single exponential decay function, providing the time constants of the long-lived components,w hich were 1.2 and 0.82 msf or 2a,b,r espectively.B ased on these results, excitedstate diagrams representingt he photophysical processes of 2a,b are shown in Figure 6.…”

“…[16] Ap icosecond laser,P L2210A (EKSPLA, 1kHz, 25 ps, 3.4 mJ for 610 nm and 2.0 mJ for 650 nm), and as upercontinuum (SC) radiation source (SC-450, Fianium, 20 MHz, pulse width:5 0-100 ps depending on the wavelength, 450-2000 nm) were employed as the pump-pulse and probe sources, respectively.A6 10 or 650 nm laser pulse was used to excite the samples. [16] Ap icosecond laser,P L2210A (EKSPLA, 1kHz, 25 ps, 3.4 mJ for 610 nm and 2.0 mJ for 650 nm), and as upercontinuum (SC) radiation source (SC-450, Fianium, 20 MHz, pulse width:5 0-100 ps depending on the wavelength, 450-2000 nm) were employed as the pump-pulse and probe sources, respectively.A6 10 or 650 nm laser pulse was used to excite the samples.…”

“…Transient absorption measurements on the nanosecond to microsecond time scale were conducted by the randomly interleaved pulse train (RIPT) method. [16] Ap icosecond laser,P L2210A (EKSPLA, 1kHz, 25 ps, 3.4 mJ for 610 nm and 2.0 mJ for 650 nm), and as upercontinuum (SC) radiation source (SC-450, Fianium, 20 MHz, pulse width:5 0-100 ps depending on the wavelength, 450-2000 nm) were employed as the pump-pulse and probe sources, respectively.A6 10 or 650 nm laser pulse was used to excite the samples. The measurements were performed in aC H 2 Cl 2 solution placed in a2-mm quartz cell under stirring at r.t.…”