TWISTED CHARGE-TRANSFER PROCESS OF NILE RED IN HOMOGENEOUS SOLUTION AND IN FAUJASITE ZEOLITE

Steady-state and time-resolved emission studies on Nile Red, a biologi cal fluorescent probe, in homogeneous solutions and in zeolite 13X and LZY are reported. It is shown that at moderately high polarity the ma in nonradiative pathway of Nile Red is twisted intramolecular charge t ransfer (TICT) process, the rate of which increases exponentially with increase in polarity (E(T)(30)) of the medium. Due to this polarity-d ependent TICT process Nile Red is a sensitive indicator of the micropo larity of biological environments. From the comparison of the emission properties of Nile Red in zeolite X and Y with those in homogeneous s olutions the E(T)(30) values of zeolite 13X and LZY are estimated to b e 55.5 +/- 1. This indicates the polarity of the zeolites is similar t o that of an aqueous methanol solution.