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

Abstract

In molecular solar energy harvesting systems, quantum mechanical features may be apparent in the physical processes involved in the acquisition and migration of photon energy. With a sharply declining distance-dependence in transfer efficiency, the excitation energy generally takes a large number of steps en route to the site of its utilization; quantum features are rapidly dissipated in an essentially stochastic process. In the case of engineered dendrimeric polymers, each such step usually takes the form of an inward hop between chromophores in neighboring generation shells. A physically intuitive, structure-determined adjacency matrix formulation of the energy flow affords insights into the key harvesting and inward funneling processes. A numerical method based on this analytic approach has now been developed and is able to deliver results on significantly larger dendrimeric polymers, with the help of large multi-processor computers. Central to this study is the interpretation of key features such as the relevance of a spectroscopic gradient and the presence of traps or irregularities due to conformational changes and folding. With the objective of fine-tune the funneling process, this model now allows the incorporation of parameters derived from quantum chemical calculations, affording new insights into the detailed operation of the harvesting process in a variety of dendrimer systems

Mechanisms of Light Energy Harvesting in Dendrimers and Hyperbranched Polymers

“…Finally, with a numerical quantum propagator [101] providing for the non-stationary wavefunction to be followed in time, the exciton can be monitored as it moves through the generations of the dendrimer, towards the accepting core. A typical time evolution of the net excitation density for the different dendrimer generations is exhibited in Figure 10 [99]. The results show excitation cascading towards the core through successive spectroscopic gradients; the propensity for each forward (core-directed) transfer is significantly greater than for backward transfer.…”

“…Moreover, the efficiency of each routing is determined by the architecture of the dendrimer and the photophysical properties of the component chromophores. Attempting to capture such features in recent work, Andrews and Jones have exhibited preliminary results from calculations using an electron dynamics model [99,100]. In these studies, density functional theory (DFT) calculations, employing the B3LYP hybrid density functional in conjunction with the 6-31G(d) basis set, are first used to optimize the molecular geometries of the chromophores, and the phenalene core, of a third-generation phenylacetylene dendrimer.…”

Energy harvesting: an integrated view of materials, devices and applications

“…An intermediate-band material based on the thiospinel semiconductor MgIn 2 S 4 was reported as a high efficiency photovoltaic material for intermediate-band solar cells [61]. Other materials have been reported with similar effects [62][63][64]. We now begin a discussion of the specific topics in this section with the variety of structures in section 3.2.…”