Charge-coupled detector , time-resolved

Figure 1. Time-resolved X-ray diffraction experiment (schematic). The liquid sample is excited by a laser pulse, and its temporal evolution is monitored by a time-delayed X-ray pulse. The diffracted radiation is measured by a charge-coupled detector (CCD). In practice, the laser and X-ray beams are not perpendicular to each other, but nearly parallel.

During the last two decades, there has been an enormous increase in the use of photophysical methods in supra-molecular chemistry. Until recently, photophysical methods, such as transient spectrometry and time-resolved fluorescence spectrometry, were primarily research tools in the arenas of photokinetics of small molecules, materials physics, and biophysics. This situation changed dramatically with the introduction of commercial, user-friendly electro-optical components such as charge-coupled detector (ED)-based spectrometers, solid-state pulsed lasers, and other instrumentation necessary for time-resolved measurements. As a result, time-resolved spectrometry became more available to the community of supramolecular chemists, who now reached the level of sophistication that can benefit from the new horizons offered. 

The Experimental Technique chapter describes our experimental setup with the following main parts laser source (Ar, excimer, Nd-YAG, nitrogen, dye, OPO), imaging monochromator, gated detector (Intensified Charge Coupled Device) and computer with corresponding software. The main features of the experimental devices are described, which enable us to accomphsh time-resolved detection. 

Since 1997, we have been using in our laboratory an intensified charge-coupled device (ICCD, Oriel model Instaspec V, with a minimum temporal gate of 2.2 ns) in a daily basis for time resolved luminescence studies. The detector has 512x128 pixels in a maximum spectral range of 200 to 900 nm. With a single laser pulse, a fluorescence or a phosphorescence spectrum can be instantaneously obtained, since the combined use of the delay unit and time gate enables one to separate prompt from delayed emissions. 

Time-resolved absorption spectra of samples of BZP/C12- 1700/EtOH and Cl 2-I5OO/H2O samples were obtained by the use of diffuse reflectance laser flash photolysis technique, developed by Wilkinson et al. [2-4]. In this study, the use of an intensified charge-coupled device as a detector allowed us to obtain time-resolved absorption spectra with nanometer spectral spacing (i.e., where the 200-900 scale is defined by the 512 pixels used for recording spectra in the array of the ICCD) [1,8-14]. 

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