ENERGY TRANSFER AMONG FLUORESCENT MOLECULES DISPERSED IN THIN FILMS OF POLYMER OR PROTEIN (RHODAMINE B, SULFORHODAMINE 101, POLYVINYL, POLY (VINYL ALCOHOL) BOVINE SERUM ALBUMIN, TIME-CORRELATED PHOTON COUNTING, LIFETIMES).

摘要

Previous research using pulsed time-resolved fluorescence techniques has shown that because rhodamine B (RHB) has an appreciable overlap of absorption and emission spectra, a system of RHB molecules dispersed in poly(vinyl alcohol) (PVOH) can collect light energy and transfer the energy of the excited state, or exciton, among the RHB molecules and to trap sites. Such a system could be technologically useful if it can improve the effectiveness of proposed photochemical conversion systems by increasing their collection efficiency. This is similar to the coupling of the antenna pigment network of plants with the specialized photosynthetic conversion center.;Toward further improving the antenna system, sulforhodamine 101 (SR101) was identified as having superior spectral properties that allow increased excitonic transfer distances, but its fluorescence lifetime was too short to be studied using existing pulsed techniques.;Because short fluorescence lifetimes do not affect the fluorescence response for continuous excitation, a steady state technique was used to determine excitonic diffusion coefficients for the separately characterized RHB system. The results were in good agreement with those previously reported, but this approach recovers less information than the time-resolved technique and is time consuming. To improve the resolution of the existing time-resolved techniques, an instrument was assembled using the ultra-short pulses of a mode-locked laser for sample excitation. The 1100 psec pulse width attained provides sufficient timing resolution to study decay rates greater than about 2 nsec without deconvolution.;From time-resolved studies of SR101 dispersed in PVOH, a diffusion length of 140 (ANGSTROM) was determined. Although this system has a greater transfer length than the RHB system, increased formation of aggregates causes the overall collection efficiency of the system to be lower.;However, the RHB system has a limited excitonic diffusion length r = (6D(tau))(' 1/2) = 120 (ANGSTROM), and is prone to forming non-fluorescent aggregates that wastefully remove energy from the system.;Because SR101 can be bound in bovine serum albumin (BSA) at high concentration without dimer formation, films of BSA containing SR101 were studied. Aggregate formation was greatly reduced and the maximum diffusion length observed was 350 (ANGSTROM).