Fluorescence picosecond time-resolved single

Fluorescence Picosecond Time-Resolved Single Photon Counting... 

For fluorescence decay curves of the J-aggregate LB films of [CI-MC] mixed with various matrix agents, measured with a picosecond time-resolved single photon counting system, three components of the the lifetimes fitting to exponential terms in the following equation ... 

The rotational reorientation times of the sample in several solvents at room temperature were measured by picosecond time-resolved fluorescence and absorption depolarization spectroscopy. Details of our experimental setups were described elsewhere. For the time-correlated single photon counting measurement of which the response time is a ut 40 ps, the sample solution was excited with a second harmonics of a femtosecond Ti sapphire laser (370 nm) and the fluorescence polarized parallel and perpendicular to the direction of the excitation pulse polarization as well as the magic angle one were monitored. The second harmonics of the rhodamine-640 dye laser (313 nm 10 ps FWHM) was used to raesisure the polarized transient absorption spectra. The synthesis of the sample is given elsewhere. All the solvents of spectro-grade were used without further purification. 

The next chapter by Ohshima, Kajimoto and Fuke reviews some results obtained with linked systems, in which charge transfer is facilitated by torsional motion around a single bond. Picosecond time-resolved experiments allowed the direct measurement of the decay of the LE state and the rise of the CT state fluorescence. In some cases a third excited state, also characterized as a charge-transfer state, was observed. It was assigned to a charge-transfer state in which the two connected moieties (anthracene and aniline in this case) are twisted from the planar conformation characteristic of the ground state, but not to a fully perpendicular conformation. The photophysics of twisted intramolecular charge-transfer (TICT) states, were studied extensively in the gas phase and in solution (see the previous chapter by Herbich and Brutschy). 

The fluorescence properties of meso-substituted amidoanthracenes have been examined also. Pyrene excimers still attract considerable interest, for example, a picosecond time resolved study has been made of excimer formation in single crystals ... 

The bimolecular reaction dynamics of geminate recombination or acid-base neutralization have until recently been studied with time-resolved techniques probing electronic transitions. Time-resolved fluorescence using time-correlated single photon counting detection is limited to a time resolution of a few picoseconds. UV/vis pump-probe experiments, in principle, may have a time resolution of a few tens of femtoseconds, but may be hampered by overlapping contributions of... 

Chapter 6 described the current techniques employed in time-resolved fluorescence spectrocopy. The time resolution of these techniques ranges from a few picoseconds (streak cameras) to a few hundreds of picoseconds (single-photon timing with flash lamp excitation). The time resolution can be greatly improved by using the fluorescence up-conversion technique. 

The time-resolved techniques that are usually used for FLIM are based on electronic-basis detection methods such as the time-correlated single photon counting or streak camera. Therefore, the time resolution of the FLIM system has been limited by several tens of picoseconds. However, fluorescence microscopy has the potential to provide much more information if we can observe the fluorescence dynamics in a microscopic region with higher time resolution. Given this background, we developed two types of ultrafast time-resolved fluorescence microscopes, i.e., the femtosecond fluorescence up-conversion microscope and the... 

The great sensitivity of fluorescence spectral, intensity, decay and anisotropy measurements has led to their widespread use in synthetic polymer systems, where interpretations of results are based upon order, molecular motion, and electronic energy migration (1). Time-resolved methods down to picosecond time-resolution using a variety of detection methods but principally that of time-correlated single photon counting, can in principle, probe these processes in much finer detail than steady-state techniques, but the complexity of most synthetic polymers poses severe problems in interpretation of results. 

A streak camera which has 12 ps shot-to-shot jitter has been developed. With this degree of precision, a simple method of signal averaging of picosecond fluorescence events may be employed direct summation. This results in a substantial increase in the signal-to-noise ratio of time-resolved fluorescence measurements over single-shot records. 

---