Multiexponential lifetime averaging

Steady-state behavior and lifetime dynamics can be expected to be different because molecular rotors normally exhibit multiexponential decay dynamics, and the quantum yield that determines steady-state intensity reflects the average decay. Vogel and Rettig [73] found decay dynamics of triphenylamine molecular rotors that fitted a double-exponential model and explained the two different decay times by contributions from Stokes diffusion and free volume diffusion where the orientational relaxation rate kOI is determined by two Arrhenius-type terms ... 

A typical image obtained by nondescanned detection and two-photon excitation is shown in Fig. 5.78. The autofluorescence of aortic tissue was excited at 800 nm. The figure shows the intensity image, an image of the average lifetime, and the lifetime distribution over the pixels. The fluorescence decay displayed for a selected pixel is multiexponential, as is typical for autofluorescence. 

When the multiexponential dKay law is used, it is often useful to determine the average lifetime (t). The average lifetime is given by Eq. [4.3], For a double.exponential decay, T is given by... 

When A is present, the decay rate of excited D is increased by energy transfer, which is strongly dependent on the D-A distance. If D and A ions distribute randomly in space, there is a transfer-rate distribution. This means a lifetime distribution resulting in multiexponential or nonexponential decay of the D excited-state population N t) in the presence of A. In this case, the average excited-state lifetime ((x)) can be calculated by... 

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