Organic/Metal-Organic Materials Chemistry

Our research focuses on the synthesis and characterization of photofunctional organic/metallo-organic materials for optical limiting and/or photodynamic therapy applications.

Optical limiting materials are nonlinear optical materials that can transmit most of the light at low intensities, but absorb, reflect, refract, or scatter light at high incident intensities for the protection of human eyes and optical sensors. Nonlinear absorption, particular reverse saturable absorption and two-photon absorption, has long been recognized as useful for optical limiting, however, it is not currently possible to a-prior design molecules that exhibit large nonlinear absorption. To remedy this deficiency, the relationship between nonlinear absorption and molecular structure must be explored. Organic/metallo-organic complexes are ideal candidates for this application because of their large, fast, and broadband optical nonlinearity. In addition, the chemical structures of these complexes can be easily modified. The complexes currently under study include nanoparticle-expanded metalloporphyrin composites, transition-metal terpyridyl acetylide complexes (Figure 1), polyads, and dendrimers, and stilbazolium derivatives. This project involves organic synthesis, spectroscopic studies (UV-Visible absorption, transient absorption, fluorescence and phosphorescence), and nonlinear optical characterization (using degenerate four wave mixing, Z-scan and nonlinear absorption techniques).

Figure 1. Transition-metal terpyridyl acetylide complexes

Photodynamic therapy (PDT) is an emerging cancer treatment method based on the interaction of light, a photosensitizer, and oxygen. It has specific selectivity comparing to other cancer treatment modalities. Unfortunately, limitations of current photosensitizers, such as toxicity, inability to treat deeply situated cancers, cutaneous photosensitivity, and water insolubility prevent the widespread use of PDT to date. In order to overcome these limitations, a series of water-soluble pentaazadentate porphyrin-like rare-earth complexes (Figure 2) and core-modified Texaphyrins that can absorb near-infrared light are being synthesized and investigated in my group. A variety of spectroscopic and structural methods including UV-VIS, IR, MS, NMR, X-ray crystallography, fluorescence and phosphorescence spectroscopy, transient absorption, and spin-trapping electron paramagnetic resonance (EPR) spectroscopy are being used to characterize the structures and to investigate the photophysics and photosensitization mechanisms of the complexes.

Figure 2. Pentaazadentate porphyrin-like rare-earth complexes

Selected Publications

B. Wang, A. Raphael, Y. Li, A. Singh, H. Lee, W. Sun* and P. R. Sharp*,  “Remarkable bromination and blue-emission of 9-anthracenyl Pt(II) complexes”,  J. Am. Chem. Soc. 131(9), 3150-3151 (2009).

P. Shao, Y. Li, A. Azenkeng, M. Hoffmann, W. Sun*,  “Influence of Alkoxyl Substituent on 4,6-Diphenyl-2,2’-bipyridine Ligand on Photophysics of Cyclometalated Platinum(II) Complexes: Admixing Intraligand Charge Transfer in Low-lying Excited States”,  Inorg. Chem.. 48(6), 2407-2419 (2009).

H. Zhang, B. Zhang,Y. Li, W. Sun,*  “Acid-Sensitive Pt(II) 2,6-Di(pyridin-2-yl)pyrimidin-4(1H)-one Complexes”,  Inorg. Chem. 48(8), 3617-3627 (2009).

Z. Ji, A. Azenkeng, M. Hoffmann, W. Sun*,  “Synthesis and Photophysics of 4′-R-2,2′;6′,2″-terpyridyl (R = Cl, CN, N(CH3)2) Platinum(II) Phenylacetylide Complexes”,  Dalton Trans. 7725-7733 (2009).

I. Mathew, W. Sun*,  “Photophysics of Pt(II) 4,6-Dipheny-2,2’-bipyridyl Complexes in Solution and LB Film”,  J. Organometallic Chem. 694, 2750-2756 (2009).

Y. Li, T. M. Pritchett, P. Shao, J. Haley, H. Zhu, W. Sun*,  “Excited-state absorption of mono-, di- and tri- nuclear cyclometalated platinum 4,6-diphenyl-2,2’-bipyridyl complexes”,  J. Organometallic Chem. 694, 3688-3691 (2009).

Q. Dai, Y. Li, L. Zhai*, W. Sun*,  “3,4-Ethylenedioxythiophene (EDOT)-Based π-Conjugated Oligomers: Facile Synthesis and Excited-state Properties”,  J. Photochem. Photobio. A: Chemistry  206, 164-168 (2009)

Z. Ji, Y. Li, W. Sun*  “Acid/base sensitive platinum terpyridyl complex: Switching between metal-to-ligand charge transfer (MLCT), ligand-to-ligand charge transfer (LLCT), and intraligand charge transfer (ILCT) states”,  J. Organometallic Chem. 694, 4140-4145 (2009).

W. Sun*, Y. Li, T. M. Pritchett, Z. Ji, J. Haley,  “Excited-state absorption of 4′-(5′′′-R-pyrimidyl)-2,2′:6′,2′′-terpyridyl platinum(II) phenylacetylide complexes”,  accepted by Nonlinear Optics, Quantum Optics: Concepts in Modern Optics (2009).

R. Subramaniam, Y. Xiao, Y. Li, S. Qian, W. Sun, S. Mallik*,  “Synthesis of coumarin-based UV one-photon and NIR two-photon cleavable lipids”,  accepted by Tetra. Lett. (2009).

Y. Li, T. M. Pritchett, J. Huang, M. Ke, W. Sun*  “Nonlinear refraction of peripheral-substituted zinc phthalocyanines investigated by nanosecond and picosecond Z-scan”,  submitted to J. Phys. Chem. Lett. (2009).

Z. Ji, S. Li, W. Sun*,  “Back-to-back dinuclear platinum terpyridyl complexes: Synthesis and photophysical studies”,  submitted to Inorg. Chem. (2009).

I. Mathew, W. Sun*,  “Influence of alkyl chain length and counterion on intermolecular interactions and vapochromic effect of Pt(II) 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine complexes: photophysical studies in solutions, solvent-induced aggregates and LB films”, submitted to Dalton Trans. (2009).

I. Mathew, Y. Li, W. Sun*,  “Dinuclear Platinum(II) 4,6-Diphenyl-2,2’-bipyridine Complexes Tethered by Rigid Bridging Ligand: Synthesis and Photophysics in Solution and in LB Film”, submitted to Inorg. Chem. (2009).

P. Shao, Y. Li, W. Sun*,  “Cyclometalated Platinum 6-Phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2′-bipyridine Complexes: Synthesis, Photophysics and Nonlinear Absorption”,  submitted to Inorg. Chem. (2009).

J. Yi, B. Zhang, P. Shao, Y. Li, W. Sun*,  “Synthesis and Photophysics of Platinum(II) 6-Phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2′-bipyridine Complexes with Phenothiazinyl Acetylide Ligand”,  submitted to Inorg. Chem. (2009).

T. Lu, P. Shao, I. Mathew, A. Sand, W. Sun*,  “Synthesis and Photophysics of Benzotexaphyrin: A Near-IR Photosensitizer and Emitter”,  J. Am. Chem. Soc. 130(47), 15782-15783 (2008).

Y. Li, D. Dini, M. J. F. Calvete, M. Hanack, W. Sun*,  “Photophysics and Nonlinear Optical Properties of Tetra- and Octabrominated Silicon Naphthalocyanines.”,  J. Phys. Chem. A.  112(3), 472-480 (2008).

P. Shao, Y. Li, W. Sun*,  “Cyclometalated platinum(II) complex with strong and broadband nonlinear optical response”,  J. Phys. Chem. A.  112(6), 1172-1179 (2008)

P. Shao, Y. Li, W. Sun*,  “Platinum(II) 2,6-bis(2’-pyridyl)-4-(4’-tolyl)-1,3,5-triazyl complexes: synthesis and photophysics”,  Organometallics  27(12), 2743-2749 (2008)

W. Jia, F. Guo, E.P. Douglas, W. Sun,*  “Two-photon absorption and degenerate four-wave mixing studies of sulfide semicondoctors in polymeric solutions”,  J. Nanosci. Nanotech.  8, 1364-1370 (2008)

T. M. Pritchett*, W. Sun, F. Guo, B. Zhang, M. J. Ferry, J. E. Rogers-Haley, W. Shensky III, A. G. Mott,  “Excited state absorption and photophysical parameters of a terpyridyl platinum(II) pentynyl complex”, Opt. Lett.  33 (10), 1053-1055 (2008).

Y. Li, T. M. Pritchett, J. Huang, M. Ke, P. Shao, W. Sun*,  “Photophysics and nonlinear absorption of peripheral substituted zinc phthalocyanines”,  J. Phys. Chem. A  112 (31), 7200-7207 (2008).

Z. Ji, Y. Li, W. Sun*,  “4’-(5’’’-R-Pyrimidyl)-2,2’:6’,2’’-terpyridyl (R = H, Cl, Ph, CN, OEt) Platinum(II) Phenylacetylide Complexes: Synthesis and Photophysics”,  Inorg. Chem. 47(17), 7599-7607 (2008).

W. Sun*, G. Wang, Y. Li, M.J.F. Calvete, D. Danilo, M. Hanack,  “Axial halide ligand effect on photophysics and optical limiting of some indium naphthalocyanines”,  J. Phys. Chem. A.  111(17), 3263-3270 (2007).

P. Shao, W. Sun*,  “Trinuclear platinum(II) 4,6-diphenyl-2,2’-bipyridine complex with bis(diphenylphosphinomethyl)phenylphosphine auxiliary ligand: synthesis, structural characterization and photophysics”,  Inorg. Chem.  46(21) 8603-8612 (2007).

W. Sun*, K. Zhong, Q. Huo, J. Brennan,  “Total chemical synthesis, Property and Modeling Studies of Nanoparticle/Polymer Hybrid Materials (II)”,  Proceeding of 2008 NSF Design, Service, and Manufacturing Grantees and Research Conference (2007).

W. Sun*, H.-J. Zhu, P. M. Barron,  “Binuclear cyclometalated platinum(II) 4,6-diphenyl-2,2’-bipyridine complexes: Interesting photoluminescent and optical limiting materials”,  Chem. Mater. 18 (10), 2602-2610 (2006).

F. Guo, W. Sun,*  “Photophysics and optical limiting of platinum (II) 4’-arylterpyridyl phenylacetylide complexes”,  J. Phys. Chem. B  110(30), 15029-15036 (2006).

G. Wang, W. Sun,*  “Optical limiting of gold nanoparticle aggregates induced by electrolytes”,  J. Phys. Chem. B  110(42), 20901-20905 (2006).

W. Sun*, P. M. Barron,  “pH sensitive photophysical and photochemical properties of a pentaazadentate porphyrin-like gadolinium complex”,  Frontiers in Bioscience.  11, 2795-2801 (2006).

F. Guo, W. Sun*, Y. Liu, K. Schanze  “Synthesis, photophysics and optical limiting of platinum (II) 4’-tolylterpyridyl arylacetylide complexes”,  Inorg. Chem. 44, 4055-4065 (2005).

M.M. McKerns*, W. Sun, C.M. Lawson, G.M. Gray,  “Higher-order triplet-triplet interaction in energy-level modeling of excited state absorption for an expanded porphyrin cadmium complex”,  J. Opt. Soc. Am. B 22 (4), 852-861 (2005).

W. Sun*, Q. Dai, J. Worden, Q. Huo,  “Optical limiting of a covalently bonded gold nanoparticle/polylysine hybrid material”,  J. Phys. Chem. B. 109 (44), 20854-20857 (2005).

W. Sun*, F. Guo,  “Excited state absorption and optical limiting of platinum(II) 4’-arylterpyridyl acetylide complexes”,  Chin. Opt. Lett. S3, S34-S37 (2005).

C.C. Byeon, M.M. McKerns, W. Sun, T.M. Nordlund, C.M. Lawson*, G.M. Gray,  “Excited state lifetime and intersystem crossing rate of asymmetric pentaazadentate porphyrin-like metal complexes”,  Appl. Phys. Lett.  84 (25), 5174 (2004).

W. Jia, E.P. Douglas, F. Guo, W. Sun*,  “Optical limiting of semiconductor nanoparticles for nanosecond laser pulses”,  Appl. Phys. Lett.  85 (26), 6326-6328 (2004).

W. Sun*, Z.-X. Wu, Q.-Z. Yang, L.-Z. Wu, C.-H. Tung,  “Reverse saturable absorption of platinum ter/bipyridyl polyphenylacetylide complexes”,  Appl. Phys. Lett. 82 (6), 850-852 (2003).

W. Sun*, T. Carvalho, M.M. Bader,  “Third-order optical nonlinearities of a,w-Dithienylpolyenes and oligo(thienylvinylene)”,  Opt. Commun. 215, 185-190 (2003).

W. Sun*, P.H. Patton, L. K. Stultz, J.-P. Claude,  “Resonant third-order nonlinearities of tetrakis(2,2’-dipyridyl)diruthenium complexes”, Opt. Commun. 218, 189-194 (2003).