Miljanić Group Meeting / Literature University of Houston ▪ Houston, TX ▪ January 16 th...
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Transcript of Miljanić Group Meeting / Literature University of Houston ▪ Houston, TX ▪ January 16 th...
M i l j a n i ć G r o u p M e e ti n g / L i t e r a t u r eU n i v e r s i t y o f H o u s t o n ▪ H o u s t o n , T X ▪ J a n u a r y 1 6 t h 2 0 0 9
Gary L loyd L im
ParacyclophenylenesCarbon Nanohoop Structures
Great Minds behind the Research
Carolyn BertozziPhD—University of California, Berkeley (1993)Predoc—Office of Naval Research (1988–1991)Diploma—Harvard University (1988)Professor at University of California, Berkeley
Jeffrey NeatonPostdoc—Rutgers University, Physics (2000–2003)
The Molecular Foundry, LBNL (2003–2005)PhD (Physics)—Cornell University (2000)Diploma—University of Minnesota (1995)Facility Director—Theory of Nanostructured Materials Facility
Joydeep Bhattacharjee—NCN Postdoc
Ramesh Jasti—University of California, Berkeley
Jasti, R.; Bhattacharjee, J.; Neaton, J.; Bertozzi, C. J. Am. Chem. Soc. 2008, 130, 17646.
California and Its Diversity
• Located on West Coast of the US • 3rd largest state (163, 696 sq. mi.)• Capital city is Sacramento• Most populous state (36,756,666)• Gross State Product of $1.812 trillion (2007)• Climate varies from Mediterranean to subartic• Well-known Universities in California:
University of California (10 campuses)
California Institute of Technology
Stanford University
Cycloparaphenylene Is a Synthetic Challenge
n
strained and distorted aromatic systems
Parekh, V. C.; Guha, P. C. J. Indian Chem. Soc. 1934, 11, 95.Jagedeesh, M. N.; Makuy, A.; Chandrasekhar, J. J. Mol. Model. 2000, 6, 226.
radially oriented p-orbitals
MeO OMe
I I
provides the curvature and rigiditynecessary for macrocyclization
3,6-syn-dimethoxy-cyclohexa-1,4-diene
Macrocylic precursors were prepared
MeO OMe
Bpin Bpin
MeO OMe
Bpin Bpin
MeO OMe
I I
Pd(PPh3)4, Cs2CO3
toluene/methanol (10:1), 80 oC
MeO
MeO OMe
m
OMe m = 2, 2% 3, 10% 5, 10%
Alonso, F.; Yus, M. Tetrahedron 1991, 47, 7471.Song, Z. Z.; Wong, H. N. C. J. Org. Chem. 1994, 59, 33.
MeO OMe
I I
I
I
1. i. nBuLi, THF, -78 oC ii. benzoquinone
2. i. NaH, THF, O oC ii. MeI, O oC to room temp.
i. nBuLi, THF, -78 oC
ii. isopropyl pinacol boronate (Bpin), -78 oC
34%
It is possible to convert cyclohexadiene moiety to aryl ring
MeO
.
e-
MeO
Lie-
Liu, H.-J.; Yip, J., Shia, K.-S. Tetrahedron Lett. 1997, 38, 2253.
MeO
MeO OMe
m
OMe
n
Li+-
THF, -78 oC
n = 5, 43% 8, 52% 14, 36%
.
What are the Properties of the Cycloparaphenylenes?
Nijegorodov, N. I.; Downey, W. S.; Danailov, M. B. Spectrochim. Acta, Part A 2000, 56, 783.
n
UV-Vis Absorption Spectra: lmax ≈ 340 nm
Fluorescence Spectra: as carbon nanohoop size decreases, the Stokes shift increases
Rings Are in a Staggered Configuration
Even-membered nanohoops, [12]- and [18] cycloparaphenylenes, have dihedral angles of 33o and 34o between two adjacent phenyl rings
Strain energies of 28 and 5 kcal mol−1 with diameters of 1.7 and 2.4 nm, respectively
Odd-membered nanohoop, [9] cycloparaphenylene, has varying dihedral angles of 18o, 30o, 31o and 34o around the carbon nanohoop
Strain energy of 47 kcal mol−1 with a diameter of 1.2 nm
Understanding its properties using Density Functional Theory
Eg = IP – EA – Ee-h IP = ionization potential
EA = electron affinity
Ee-h = electron-hole interaction energy
•IP – EA decreases as the number of phenyl rings increase
•Ee-h grows dramatically with the decreasing number of phenyl rings
Large Stokes shift observed is governed by the degree of structural relaxation in the optically excited state
Enhanced curvature leads to greater sp3 hybridization and increasingly asymmetric p-orbital
Cycloparaphenylenes Are Remarkable
1) Cycloparaphenylenes can be synthesized using a masked aromatic ring moiety
2) Cycloparaphenylenes are subunits of an armchair carbon nanotube
3) Possible route to extended carbon nanotubes using solution-phase chemistry
4) Preparation of carbon nanotubes of a specific chirality