Blinking behaviour

As far as the blinking behaviour is concerned, we recall here that extensive studies on small organic molecules have highlighted the major role played by the presence of the triplet states. After a certain number of excitation cycles triplet excited states can be populated, leaving the system in a dark state for several milliseconds [61], if not seconds, as in the case of PFO at low temperatures as witnessed by the phosphorescence lifetime [62], The absence of blinking in the P phase suggests that triplet formation is indeed very inefficient under optical excitation. Generally, in the case of multichro-... 

Fig. 8 (a) Schematic showing a nanocrystal going from an on state to an off state at random times, (b) Simulation of blinking behaviour at various timescales in a typical nanocrystal. Note the self-similarity of the blinking phenomenon on many timescales, (c) The power law distribution of lifetimes represents a sum of a large number of exponential processes. 

A third potential threat to proper FRAP analysis is the blinking behaviour of GFP. It has been shown that many fluorescent proteins rapidly switch between a dark non-fluorescent state and a fluorescent state. The period GFPs are in the dark state (off-time) is not dependent on laser whereas the on-times are [37,38]. Since the bleach pulse is at a much higher intensity as the monitoring after bleaching, it can be expected that a part of the recovery of fluorescence is due to decrease of the pool of molecules in the off-state. This is not a great problem if all conditions are kept constant, since it will only introduce a constant bias in the results However, comparison between different variants of GFP that have different blinking properties is hampered. 

Dickson R M, Cubitt A B, Tsien R Y and Moerner W E 1997 On/off blinking and switching behaviour of single molecules of green fluorescent protein Nature 388 355-8... 

R. M. Dickson, A.B. Cubitt, R.Y Tsien, and W. E. Moerner, On/Off Blinking and Switching Behaviour of Single Molecules of Green Fluorescent Protein, Nature 388,... 

Other prominent applications of these materials include devices such as QD-LEDs, " ° IR photodetectors, active elements in devices such as sensors, lasers etc. With an understanding of the processes controlling the final properties of these materials, we can now control defects, reduce blinking and alter the surface properties to the required hydrophobic behaviour while retaining the interesting properties necessary for any particular application. 

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