The Dynamics of Electronic Energy Transfer in Novel Multiporphyrin Functionalized Dendrimers:  A Time-Resolved Fluorescence Anisotropy Study

Abstract

The dynamics of electronic energy transfer (EET) for a series of spherical porphyrin arrays based on different generations of poly(propylene imine) dendrimers have been investigated using time-resolved fluorescence anisotropy measurements (TRAMS) in a glass environment. The first, third, and fifth generation dendrimers consisting of 4, 16, and 64 porphyrin chromophores, respectively, are investigated in this study. We observe a depolarization of the fluorescence in all three dendrimers as compared to the monoporphyrin model compound, indicating that EET takes place between the chromophores within the dendrimers. The experimental TRAMS results were compared to computationally simulated data obtained from the Pauli master equation. For the first generation dendrimer, we find the rate of energy transfer is well described by Förster theory. Anomalous behavior is observed in the third generation dendrimer where the limiting anisotropy value suggests that energy transfer is confined to only the porphyrins contained within a dendron. Interdendron porphyrin EET is thus unfavorable due to dendron segregation. In the fifth generation dendrimer, the TRAMS data is best explained by a model which includes independent and simultaneous rapid EET between porphyrins contained on the surface of the dendrimer sphere and slow EET between porphyrins in adventitious dendrons found probably either outside or inside of the sphere.

Tailoring Fluorescence Brightness and Switching of Nanoparticles through Dye Organization in the Polymer Matrix

“…Excitation energy transfer inside the NPs was then studied to further understand the observed differences in the ensemble behavior of the encapsulated dyes. 42 As energy transfer between randomly oriented dyes leads to depolarization of the emitted light, 43,44 we measured steady-state and time-resolved fluorescence anisotropy of these NPs (Figure 4). The steady-state anisotropy decreased much faster with dye-loading for PLGA NPs than for PMMA and PCL NPs, especially in the region up to 1 wt%.…”

On the nature of long range electronic coupling in a medium: Distance and orientational dependence for chromophores in molecular aggregates

“…4,6,[36][37][38][39][40] The other approach employs the PME, where the rate constants are used to describe the population transfer between sites. 6,[41][42][43][44] It is important to point out that while the first approach explicitly includes quantum coherent effects into the dynamics, the PME approach describes incoherent transport, with quantum effects (i.e., interference terms) being included implicitly through the rate constants.…”

Primary Photonic Processes in Energy Harvesting: Quantum Dynamical Analysis of Exciton Energy Transfer over Three-Dimensional Dendrimeric Geometries

“…40 Yeow et al developed a theoretical approach which employed the Pauli master equation to help understand time-resolved fluorescence anisotropy measurements that were made on a series of porphyrin-based dendrimers. 41 Nakando et al used a quantum master equation approach for modeling the second hyperpolarizability of nanostar dendrimers; 42 May et al employ a mixed quantum classical methodology to calculate rates of energy transfer in the pheophorbide-a DAB dendrimer, 43,44 and Fernandez-Alberti have used non-adiabatic trajectories to model energy transfer in dendrimeric units. 45 One of the authors of the current paper (Andrews) and collaborators have recently developed an adjacency matrix approach that has been used to model the multi-step flow of energy in light-harvesting dendrimers.…”