INTERPLAY OF HYDROGEN BONDING AND ELECTRONIC STRUCTURE ON THE OPTOELECTRONIC PROPERTIES OF GUANINE-TERMINATED OLIGOMERS
Danielle E. Fagnani,1 Dylan E. Holst,1 Daken J. Starkenburg,2 Jiangeng Xue,2 and Ronald K. Castellano1
1 Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville FL 32611-7200, USA
2 Department of Materials Science and Engineering, University of Florida, P.O. Box 116400, Gainesville, FL 32611-6400, USA
Semiconducting, π-conjugated organic molecules are attractive for many modern optoelectronic applications. While the relationship between molecular structure and intrinsic optical and electronic properties is well understood, the effect of supramolecular packing on solid-state properties in thin films, and consequences on performance in applied settings, has yet to be rigorously established. We are currently using a hierarchical self-assembly approach to investigate this relationship; nanoscale to mesoscale order in thin films can be achieved by equipping conventional π-systems with robust hydrogen bonding units. In this particular work, we are constructing a set of linear π-conjugated oligomers covalently linked to guanine (G), one of the DNA nucleobases, or a protected guanine (PG) comparator at each terminus. Guanine is known to form tetramers (known as the “G-quartet” in biology) that have the ability to template highly ordered 2-D π-conjugated frameworks in thin films and further encourage 3-D order via π-π stacking; these capabilities are weakened for PG derivatives. The goal of this work is to understand how the molecular recognition capabilities of these guanine-containing π-conjugated oligomers (via hydrogen-bonding) manifest in the solid-state thin films and may systematically affect the bulk properties of π-conjugated materials in diagnostic devices.
HALOGEN BONDING INDUCED SUPRAMOLECULAR ASSEMBLY OF A LOW-ENERGY-GAP π-CONJUGATED OLIGOMER AND THERMAL ACTIVATION OF COMPLEMENTARY HYDROGEN BONDING SITES TO FURTHER TUNE THE ASSEMBLY
Asmerom O. Weldeab,1 Suong T. Nyguen,2 Daken J. Starkenburg,3 Jiangeng Xue,3 Ronald K. Castellano1, and Davita L. Watkins2
1 Department of Chemistry, University of Florida, P.O.Box 117200, Gainesville, FL 32611-7200, USA
2 Department of Chemistry and Biochemistry, University of Mississippi, Oxford, MS 38677, USA
3 Department of Materials Science and Engineering, University of Florida, P.O.Box 116400, Gainesville, FL 32611-6400, USA
Significant effort has been made in the recent decade towards developing organic semiconductors. Despite improvements in molecular design, currently available organic semiconductors still suffer lower device efficiencies and mechanical stabilities compared to their inorganic counterparts. The poorly controllable and often random solid state arrangements of the molecules affects device efficiency (i.e., charge mobility). Increasing in the literature are supramolecular approaches which utilize hydrogen bonding (HB) to control the nanoscale to microscale arrangement of molecules in thin films. Also arising are approaches exploiting halogen bonding (XB) for similar applications.
Prepared here is a halogen bond capable C2-symmetric π-conjugated oligomeric moiety (II_Boc) with a general Donor-Acceptor-Donor design. Isoindigo and thiophenes are used as electron accepting and donating units, respectively. The molecule is end- capped with pyridine units, also part of the conjugated system, as halogen bond acceptors. The halogen bonding driven assembly of II_Boc with 1,4-diiodotetrafluorobenzene (DITFB) is confirmed experimentally by X-ray crystallography. This noncovalent interaction guides the ordering of the molecules to yield highly directional halogen bond induced 2D assemblies which stack via π-π interactions. Pyrolytic cleavage and removal of t-butyloxycarbonyl (Boc) groups, installed for solubility purposes, and subsequent exposure of the complementary hydrogen bonding sites in II_NH was also confirmed by TGA and IR. Overall, the data is consistent with 3D assembly of the molecule through synergetic halogen bonding, hydrogen bonding, and π-stacking.
Recent Advances in Homogenous Gold Catalysis: Accessing Heterocycles Containing Nitrogen Boron Bonds
Stephen Motika; Xiaodong Shi
University of South Florida
The combination of triazole/gold (TA-Au) and Cu(OTf)2 is identified as the optimal catalytic system for promoting intramolecular hydroboration for the synthesis of a six-membered cyclic amine–borane. Excellent yields (up to 95 %) and regioselectivities (5-exo vs. 6-endo) were achieved through catalyst control and sequential dilution. Good functional-group tolerance was attained, thus allowing the preparation of highly functionalized cyclic amine–borane substrates, which could not be achieved using other methods. Deuterium-labeling studies support the involvement of a hydride addition to a gold-activated alkyne with subsequent C−B bond formation
MULTIFUNCTIONALIZED MOLECULES AND MATERIALS FROM BENZOTRIFURAN(ONE)
Ronald K. Castellano
Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA
Benzotrifuranone (BTF) is a deceptively simple looking heterocycle bearing three lactone rings that our lab introduced to the community in 2009. Since this time we have come to appreciate its structure, reactivity, and more recently, potential for applications. The story begins with BTF’s unique ability to undergo selective and sequential aminolysis reactions, behavior we now confidently understand to arise from a synergism of electronic effects and a "ring strain gradient". The reactivity has recently leveraged the mild and efficient preparation of both heterodifunctionalized polymers and a molecular FRET relay system. Acylation of BTF provides access to benzotrifurans, attractive but otherwise difficultly prepared heterocycles. Described will be the first preparation and structural analysis of parent benzotrifuran (BTFuran), as well as its usefulness for accessing π-conjugated materials.
Highly efficient cellular entry and intracellular organelle targeting of
conjugated polymer nanoassembly
Md. Salauddin Ahmed, Rajeshkumar Manian, Joong Ho Moon
Department of Chemistry and Biochemistry, Biomolecular Sciences Institute, Florida International University
Although various nanomaterials offer improved payloads delivery to the diseased tissues, poor intracellular entry and lack of organelle targeting are still big huddles that substantially decrease the therapeutic effects. In this presentation, our recent efforts to achieve high cellular entry and organelle targeting using p-electron conjugated polymer nanoassembly (CPNs) will be discussed. CPNs are formed by self-assembly of non-aqueous soluble luminescent conjugated polymers (CPs), and have been used for labeling, sensing, and delivery of biological substances. By modulating the chemical structures of rigid aromatic backbone and flexible side chains, we have successfully fabricated various self-assembly structures and demonstrated modulated cellular interaction, entry, and intracellular targeting. The structure-function relationship obtained from our research will lead to novel design concepts for multifunctional cellular nanomaterials with high cellular entry and targeting efficiency.
STEP-WISE SELF-ASSEMBLY OF GIANT SUPRAMOLECULAR FRACTALS
Department of Chemistry, University of South Florida, Tampa FL 33620, USA
Self-assembly as a powerful bottom-up approach has been extensively used by nature to create complex biological systems. Synthetic supramolecular chemistry aims to use the principles of biological self-assembly to construct artificial nanostructures using molecular building blocks with desired functions and properties. The corresponding abiological assemblies, however, still suffered from a lack of complexity and thus were unable to reach the high degrees of functionality found in natural systems. With the goal of increasing the complexity of metallo-supramolecules, we designed and assembled a series of giant supramolecular architectures with fractal geometry using 2,2’:6’,2”-terpyridine ligands in a step-wise manner. This strategy allows us to harness strong and weak binding metal ions, e.g., Ru(II) with Fe(II), Zn(II) or Cd(II) through self-assembly, in which stable Ru(II)-organic ligand was assembled or synthesized for the subsequent self-assembly with metal ions with low binding strength and high reversibility to construct heteroleptic metallo-supramolecules. It is expected that this step-wise self-assembly approach will advance terpyridine-based supramolecular chemistry into a new level of sophistication through constructing supramolecular fractals with increasing complexity.
Electronic Processes in Well-Defined Nanoscale objects that Feature Single-Walled Carbon Nanotubes Wrapped by Semiconducting Polymers
Jean-Hubert Olivier,1 Michael Therien,2 Jaehong Park,2 Yusong Bai,2 George Bullard2
1 Department of Chemistry, University of Miami, Coral Gables FL 33124-0431, USA
2 Department of Chemistry, Duke University, Durham NC, 27708-0346, USA
Highly charged semiconducting polymers that feature a 2,2’-(1,3-benzyloxy)-bridged (b)-1,1’-bi-2-naphthol unit have been shown to single-chain wrap the nanotube surface with fixed helical chirality and pitch length. We demonstrate that chiral anionic semiconducting polymers that feature a perylene diimide (PDI) electron acceptor as an integral part of the polymer repeat unit provides polymer-SWNT superstructures for light-driven energy conversion reactions. Femtosecond pump-probe transient absorption spectroscopic experiments show that excitation into the SWNT E11 transition generates SWNT hole polaron [(6,5) SWNT(•+)n] and PDI radical anion (PDI−•) states. These studies demonstrate for the first time a photoinduced electron transfer process involving a SWNT and a semiconducting polymer in which: (i) the charge-separated products, and (ii) photoinduced charge separation and thermal charge recombination dynamics, are fully characterized. To fully exploit these polymer-SWNT hybrids in energy conversion applications, we have developed solution-based processes to structure dense, highly aligned arrays of these nano-objects on solid substrates. We show that ionic self-assembly approaches provide solid-state SWNT-based materials from solution that feature aligned, individualized nanotubes at high mass fraction per unit volume. The ability to modulate polymer electronic structure by design, used in conjunction with facile hierarchical organization, offers exceptional promise for the development of new types of optoelectronic nanomaterials.