Showing papers by "Rajesh S. Bhosale published in 2010"

Supramolecular n/p-heterojunction photosystems with oriented multicolored antiparallel redox gradients (OMARG-SHJs).

Abstract: Directional electron and hole transport is essential in photosynthesis. Applied to molecular optoelectronics such as organic solar cells, these lessons from nature call for oriented supramolecular n/p-heterojunctions (SHJs) that contain various chromophores and antiparallel redox gradients (OMARGs). In this tutorial review, we summarize recent progress made toward the construction of OMARG-SHJs. This conceptually innovative twist added to a timely topic should appeal to the synthetic organic, supramolecular, biological, physical, analytical and materials chemist as well as to the expert in energy and environmental sciences.

Supramolecular n/p-Heterojunction Photosystems with Antiparallel Redox Gradients in Electron- and Hole-Transporting Pathways

Abstract: Lessons from nature call for supramolecular n/p-heterojunctions with oriented multicolored antiparallel redox gradients (OMARG-SHJs) as “ideal” photosystems. Their design combines advantages of bilayer and bulk n/p-heterojunction (BHJ) solar cells for the directional separation of photogenerated charges before recombination can occur. Although conceptually attractive, OMARG-SHJs have remained beyond reach because of unresolved challenges in synthetic organic and supramolecular chemistry. Here we report the first OMARG-SHJs with two-component redox gradients in both the electron- and hole-transporting pathways. They were obtained by zipper assembly of stacks of red naphthalenediimide (NDI) electron donors along strings of oligophenylethynyl hole acceptors on top of yellow NDI electron acceptors along p-oligophenyl hole donors. The presence of both gradients is shown to be essential for achieving photoinduced charge separation over very long distances.

Zipper assembly of SHJ photosystems: focus on red naphthalenediimides, optoelectronic finetuning and topological matching

Abstract: The objective of this study was to synthesize multichromophoric donor–acceptor systems with non-halogenated red (RO) naphthalenediimides (NDIs) attached along p-oligophenyl (POP) and oligophenylethynyl (OPE) scaffolds, and to evaluate their usefulness for zipper assembly of artificial photosystems. Compared to halogenated red NDIs (RCl, RBr), the HOMO of RO is 0.2 eV higher and the HOMO/LUMO gap 0.1 eV smaller, the latter introducing a shade of pink. Consistent with higher HOMO levels, RO zippers generate less photocurrent than RBr zippers in their respective action spectra. RO zippers are less sensitive to topological mismatch than RBr zippers and thus more robust and broadly applicable. Transient absorption measurements reveal efficient electron transfer from excited OPE donors to RO acceptors and less efficient hole injection from excited RO donors into OPE acceptors. Both processes demonstrate compatibility with OMARG-SHJ photosystems (supramolecular n/p-heterojunctions with oriented multicolored antiparallel redox gradients). Decreasing hole transfer with decreasing HOMO energy differences further demonstrates that SHJ-type hole injection disappears gradually (rather than abruptly). Losses in photonic energy during this process can thus be minimized by optoelectronic finetuning, but eventual gains in open circuit voltages risk coming with complementary losses in short circuit current.

Optoelectronically mismatched oligophenylethynyl-naphthalenediimide SHJ architectures

Abstract: The objective of this study was to evaluate the possibility of photoinduced stack/rod electron transfer in surface “zipper” architectures composed of stacks of blue (B) naphthalenediimides (NDIs) along strings of oligophenylethynyl (OPE) rods. The synthesis and characterization of anionic and cationic multichromophoric OPE-B systems are reported. Absorption spectra suggest that in OPE-B systems, planarity and thus absorption and conductivity of the OPE can possibly be modulated by intramolecular stacking of the surrounding NDIs, although interfering contributions from aggregation remain to be differentiated. Among surface architectures constructed with OPE-B and POP-B systems by zipper and layer-by-layer (LBL) assembly, photocurrents generated by OPE-B zippers exhibit the best critical thickness and fill factors. These findings confirm the existence and functional relevance of topologically matching zipper architectures. In OPE-B zippers, OPEs generate much more photocurrent than the blue NDIs. Ultrafast electron transfer from OPEs to NDIs accounts for these photocurrents, providing wavelength-controlled access to rod–stack charge separation, and thus to formal supramolecular n/p-heterojunctions (SHJs). NDI excitation is not followed by the complementary hole transfer to the OPE rod. Scaffolds with higher HOMOs will be needed to integrate blue NDIs into SHJ photosystems.

Supramolecular n/p‐Heterojunction Photosystems with Oriented Multicolored Antiparallel Redox Gradients (OMARG‐SHJs)

Abstract: Directional electron and hole transport is essential in photosynthesis. Applied to molecular optoelectronics such as organic solar cells, these lessons from nature call for oriented supramolecular n/p-heterojunctions (SHJs) that contain various chromophores and antiparallel redox gradients (OMARGs). In this tutorial review, we summarize recent progress made toward the construction of OMARG-SHJs. This conceptually innovative twist added to a timely topic should appeal to the synthetic organic, supramolecular, biological, physical, analytical and materials chemist as well as to the expert in energy and environmental sciences.