MOLECULAR FLEXIBILITY AS MANIFESTED IN LIGHT-SCATTERING AND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY

The internal motion of flexible and semiflexible molecules can be described in terms of dynamical correlations between the rigid groups. In alkane chains the dynamical correlations of different groups decay with increasing distance, and above n = 8 the methylene groups move independently. In the case of molecules with one scattering group this result was obtained by following the decrease of hydrodynamic resistance with the length of the molecule. For longer chains this resistance is restricted to the friction exerted to a few units only; the rest of the chain is not involved in the motion, i.e. moves independently. For molecules labelled with two scattering groups we directly observe the correlation times of the relative motion of these two groups. The RRCTs thus found in rigid molecules agree with those obtained with one scattering group. If the connection between the scattering groups is flexible the dynamics can be analysed in terms of a correlated, and an uncorrelated motion.