Picosecond time-resolved infrared

George MW, Dougherty TP, Heilweil EJ. UV photochemistry of [CpFe(CO)2]2 studied by picosecond time-resolved infrared spectroscopy. J Phys Chem 1996 100 201-206. 

Weinstein JA, Grills DC, Towrie M et al (2002) Picosecond time-resolved infrared spectroscopic investigation of excited state dynamics in a Pt(II) diimine chromophore. Chem Comm 382-383... 

Figure 20.6 (a) Picosecond time-resolved infrared spectrum of RR-P3HT (regioregular poly (3-hexylthiophene)) at about lOOps delay time after photoexcitation [22] and (b) infrared difference spectrum of RR-P3HT doped with FeClj [23J. AAbsorbance, absorbance difference. (Source Reproduced with permission from [22] and [23], Copyright (2009) and (2003), Elsevier.)... 

Sakamoto, A., Nakamura, O., Yoshimoto, G. and Tasumi, M. (2000) Picosecond time-resolved infrared absorption studies on the photoexcited states of poly(p-phenylenevinylene). J. Phys. Chem. A, 104,4198-4202. 

Sakamoto, A. and Takezawa, M. (2009) Picosecond time-resolved infrared absorption study on photoexcited dynamics of regioregular poly(3-hexylthiophene). Synth. Met., 159, 809-812. 

Yamakata, A., Uchida, T., Kubota, J. and Osawa, M. (2006) Laser-induced potential jump at the electrochemical interface probed by picosecond time-resolved surface-enhanced infrared absorption spectroscopy./. Phys. Chem. B, 110, 6423-6427. 

Sakamoto A, Nakamura O, Tasumi M (2008) Picosecond time-resolved polarized infrared spectroscopic study of photoexcited states and their dynamics in oriented poly(p-phenylene-vinylene). J Phys Chem B 112 16437... 

Thus far, the only excited-state structural dynamics of oligonucleotides have come from time-resolved spectroscopy. Very recently, Schreier, et al. [182] have used ultrafast time-resolved infrared (IR) spectroscopy to directly measure the formation of the cyclobutyl photodimer in a (dT)18 oligonucleotide. They found that the formation of the photodimer occurs in 1 picosecond after ultraviolet excitation, consistent with the excited-state structural dynamics derived from the resonance Raman intensities. They conclude that the excited-state reaction is essentially barrierless, but only for those bases with the correct conformational alignment to form the photoproducts. They also conclude that the low quantum yields observed for the photodimer are simply the result of a ground-state population which consists of very few oligonucleotides in the correct alignment to form the photoproducts. 

We have performed super-resolution infrared microscopy by combining a laser fluorescence microscope with picosecond time-resolved TFD-IR spectroscopy. In this chapter, we have demonstrated that the spatial resolution of the infrared microscope improved to more than twice the diffraction limit of IR light. It should he relatively straightforward to improve the spatial resolution to less than 1 pm by building a confocal optical system. Thus, in the near future, the spatial resolution of our infrared microscope will be improved to a sub-micron scale. 

We have also demonstrated picosecond time-resolved TFD-IR imaging of the vibration relaxation of Rhodamine-6G in Arabidopsis thaliana roots, and found an abnormally long-lived component of vibrational relaxation in a cell. This may result from a site dependence of vibrational relaxation within whole cells. These results indicate the possible utility of the two-color super-resolution infrared microscope in mapping specific IR absorptions with high spatial resolution, and the observation of dynamics in a non-uniform environment, such as a cell. By using this infrared super-resolution microscope, we will be able to visualize the structure and reaction dynamics of molecules in a wide range of non-uniform environments. 

Sakai, M., Kawashima, Y., Takeda, A., Ohmori, T. and Fujii, M. (2007) Far-field infrared super-resolution microscopy using picosecond time-resolved transient fluorescence detected IR spectroscopy. Chem. Phys. Lett., 439, 171—176. 

In this chapter, millisecond time-resolved infrared measurements are first described in Section 20.2 for this time scale, time resolution is set by the time needed to measure (scan) a spectrum. Then, microsecond to nanosecond time-resolved measurements, which are limited by the detector response time are described in Section 20.3, and finally, picosecond to femtosecond time-resolved measurements, the time resolution for which is determined by the width of the laser pulse used for the measurement, are described in Section 20.4. 

Picosecond to Femtosecond Time-Resolved Infrared Absorption Measurements... 

Many photochemical and photophysical phenomena occur on a time scale shorter than a nanosecond. In order to follow such fast phenomena by infrared spectroscopy, picosecond to femtosecond time-resolved infrared measurements are required. Since time resolving in this time range cannot be performed by utilizing the fast-response capability of a detector and the time-resolving power of an electronic circuit (gate circuit, etc.), the following optical methods are mainly used (i) a method based on the upconversion (optical gating) process, and (ii) a method which detects pulsed infrared radiation itself. At present, the latter method is commonly used for picosecond to femtosecond time-resolved measurements. 

Picosecond to femtosecond time-resolved infrared absorption measurements were initiated in the middle of the 1980s. In 1984, Heilweil et al. [17] studied the dynamics of vibrational relaxation by using picosecond infrared pulses obtained from an OPA (LiNb03) excited by a mode-locked Nd YAG laser. 

In practice, an electromagnetic pulse with an infinitely short width does not exist, but ultrashort laser pulses are now used for various spectroscopic measurements. Terahertz spectrometry described in Chapter 19 is based on femtosecond laser pulses. In Chapter 20, time-resolved infrared spectroscopic methods using picosecond to femtosecond laser pulses are described. Such ultrashort laser pulses have large spectral widths in the frequency domain. Let us discuss the relation between the pulse width in the time domain and its spectral width expressed in either frequency or wavenumber. 

Material response in THz frequency region, which corresponds to far- and mid-infrared electromagnetic spectrum, carries important information for the understanding of both electronic and phononic properties of condensed matter. Time-resolved THz spectroscopy has been applied extensively to investigate the sub-picosecond electron-hole dynamics and the coherent lattice dynamics simultaneously. In a typical experimental setup shown in Fig. 3.5, an... 

As demonstrated, different time-resolved FTIR techniques allow to study the complete photocycle of bacteriorhodopsin in the entire range from picoseconds to several milliseconds. Infrared difference spectra trace reactions which take place in different parts of the protein molecule. Isotopically labeled proteins or proteins with mutations at specific sites... 

---