Frequency-Domain Studies of Anisotropic Rotational Diffusion

FREQUENCY-DOMAIN STUDIES OF ANISOTROPIC ROTATIONAL DIFFUSION 

Anisotropic rotati onal diffusion has been more Nct sively studied using FD methods. In fact, the earliest reports on the anisotropic rotation of fluorophores concerned experiments performed using fixed-frequency phase-modulation fluorometers. At that time the phase-modulation instruments operated at only one or two fixed hrequendes. Hence, it was not possible to recover the anisotropy decay law. The experiments were performed by measuring the differential polarized phase angles as the temperature was varied. It is relatively simple to predict the maximum value of Ao) for known values of the lifetime and fundamental anisotropy. For an isotropic rotor, the predicted value of Aw is given by 

Anisotropic rotations of perylene were detected by measurements of the tempoature-dependeat values of tan A. measured at a single modulator frequency. The values of tan A are only nonzero in the temperature range where rotational diffusion is on a dmescale comparable to the 

GLOBAL ANISOTROPY DECAY ANALYSIS WITH MULTIWAVELENGTH EXCITATION 

one expects the out-of-plane rotation to dominate the anisotropy decay. Tliese slower motions display a maximum value of Aca at lower modulation frequencies. 

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