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Cucurbit[7]Uril Host-Viologen Guest Complexes CUCURBIT[7]URIL HOST-VIOLOGEN GUEST COMPLEXES: ELECTROCHROMIC AND PHOTOCHEMICAL PROPERTIES by MARINA FREITAG A dissertation submitted to the Graduate School – Newark Rutgers, The State University of New Jersey in partial fulfillment of requirements for the degree of Doctor of Philosophy Graduate Program in Chemistry Written under the direction of Professor Elena Galoppini and approved by ________________________ ________________________ ________________________ ________________________ Newark, New Jersey October, 2011 ABSTRACT OF THE DISSERTATION Abstract Cucurbituril[7] Host - Viologen Guest Complexes: Electrochromic and Photochemical Properties By MARINA FREITAG Dissertation Director: Professor Elena Galoppini In this thesis, we demonstrated that a molecular host, cucurbit[7]uril, provides an alternative method of adsorbing molecules on semiconductors and shields the guest from the hetereogenous interface. These novel hybrid systems exhibited photophysical and electrochemical properties that differ from the properties of layers obtained by directly attaching the chromophore to the semiconductor through binding groups. This thesis describes the host-guest chemistry between cucurbit[7]uril (CB[7]) and various series of viologen guests. Methylviologen (1,1'-dimethyl-4,4'-bipyridinium dichloride, MV2+), 1-methyl-1'-p-tolyl-4,4'-bipyridinium dichloride (MTV2+), and 1,1'-di- p-tolyl-(4,4'-bipyridine)-1,1'-diium dichloride (DTV2+) were encapsulated in the macrocyclic host cucurbit[7]uril, CB[7]. The complexes MV2+@CB[7] and MTV2+@CB[7] were physisorbed to the surface of 1 TiO2 nanoparticle films. The complexation into CB[7] was monitored by H NMR. TiO2 films functionalized with the complexes were studied by FT-IR-ATR and UV-Vis ii absorption. The electrochemical and spectroelectrochemical properties of MV2+@CB[7] and MTV2+@CB[7] were studied in solution and in electrochromic windows (ECDs), where the complexes were bound to TiO2 films cast on FTO. The ECDs prepared from 2+ 2+@ MV @CB[7]/TiO2/FTO and MTV CB[7]/TiO2/FTO electrodes showed reversible, sharp and fast color switching upon application of -0.8 V. Viologen derivative DTV2+ exhibited enhanced fluorescence upon encapsulation. Aqueous solutions of DTV2+ were weakly fluorescent (Φ = 0.02, τ < 20 ps), whereas the emission of the DTV2+@2CB[7] complex was enhanced by one order of magnitude (Φ = 0.29, τ = 0.7 ns) and was blue-shifted by 35 nm. DTV2+ in polymethylmethacrylate (PMMA) matrix was fluorescent with a spectrum similar to that observed for the complex in solution. DFT and CIS calculations suggested that the increased planarity of the aromatic rings and a quinonoid structure of the S1 state, induced by encapsulation in the host, can explain the observed emission enhancement. The absorption and emission spectra of DTV2+@2CB[7] in water exhibited a large Stokes shift (ΔSt ~ 10,000 cm-1) and no fine structure. 1H NMR and UV-Vis titration indicated that the DTV2+@2CB[7] 4 complex is formed in aqueous solutions with a complexation constant of K1W = 1.2×10 -1 4 -1 4 -1 4 -1 M , K2W = 1.0×10 M in water, and K1NaCl = 1.1×10 M , K2NaCl = 0.8×10 M in 0.05 M NaCl aqueous solution. iii Acknowledgement I would like to take this opportunity, first and foremost, to thank my supervisor, Professor Elena Galoppini, for her kindness, help, guidance, and patience during my studies. It has been a pleasure studying in her research group. I would like to thank my committee members, Prof. Phillip Huskey, Prof. Jenny Lockard of Rutgers University, Newark and Prof. Angel E. Kaifer of University of Miami, Florida for their effort and time in reading and correcting my thesis. It has been a pleasure working with members of the Galoppini group, both past and present, Dr. Jonathan Rochford, Dr. Olena Taratula, Dr. Sujatha Thyagarajan, Dr. Yongyi Zhang, Andrew Kopecky, Keyur Chitre, Yan Cao, and Agnieszka Klimczak. I thank them for their constant support and motivation. I would also like to thank Prof. Piotr Piotrowiak and Prof. Lars Gundlach for their kindness and helpful discussions regarding DFT and CIS calculations. My sincere thanks also goes to Prof. Carlo A. Bignozzi and Dr. Stefano Caramori from the University of Ferrara, Italy, for offering me the research opportunity in his group and leading me working on diverse exciting projects. I wish to also thank the faculty members of the Department of Chemistry, Rutgers University for their guidance, excellent teaching and research advice, and also the staff of both the Department of Chemistry and Rutgers University, especially Judy Slocum and Monika Dabrowski, for their helpfulness. In addition, I greatly appreciate the financial assistance that has been provided by the Donors of the American Chemical Society Petroleum Research Fund for support of this research (ACS PRF #46663-AC10). iv And a special thanks goes to Richard Freitag for bearing with me during the completion of this manuscript. v Table of Contents Abstract ............................................................................................................................... ii Acknowledgement ............................................................................................................. iv Table of Contents ............................................................................................................... vi Lists of Figures .................................................................................................................. xi List of Schemes ............................................................................................................... xxii Lists of Tables ................................................................................................................ xxiii Lists of Abbreviations .................................................................................................... xxiv Chapter A ............................................................................................................................ 1 A.1 Introduction .................................................................................................................. 2 A.1.2 Nanostructured Metal Oxide Interfaces .................................................................... 7 A.2. Supramolecular Hosts on Semiconductor Surfaces .................................................. 10 A.2.1 Hemicarceplexes ..................................................................................................... 12 A.2.2 Cyclodextrins .......................................................................................................... 14 A.2.3 Calixarenes .............................................................................................................. 21 A.2.4 Zeolites .................................................................................................................... 24 A.2.6 Redox Active Compounds Bound to TiO2 .............................................................. 26 A.3 The Cucurbituril Family............................................................................................. 28 A.3.1 Cucurbit[7]uril, a Molecular Host ........................................................................... 32 vi A.5 References .................................................................................................................. 36 Chapter B .......................................................................................................................... 54 Introduction ....................................................................................................................... 55 B.2 Synthesis of Viologen Derivatives ............................................................................. 59 B.2.1 Synthesis of Alkyl Viologens .................................................................................. 59 B.2.2 Synthesis of Aryl Viologens ................................................................................... 61 B.3 Host-Guest Complexes of Viologens with Cucurbit[7]uril........................................ 63 1 2+ 2+ B.3.1 H NMR study of MV @CB[7] and MTV @CB[7] ........................................... 65 B.3.2 Complexation Constant* ......................................................................................... 68 B.4 Cucurbituril Complexes Bound to TiO2 ..................................................................... 69 B.4.1 Preparation of nanostructured TiO2 Films .............................................................. 71 B.4.2 Binding on Nanostructured TiO2 Films .................................................................. 72 B.5 Electrochemistry......................................................................................................... 73 B.5.1 Cyclic Voltammetry Measurements in Solution ..................................................... 73 B.6 UV-Vis Absorption Spectroscopy ............................................................................ 77 B.6.1 UV-Vis Absorption Spectra in Solution.................................................................. 77 B.6.2 UV-Vis Absorption Measurements of Electrochromic Windows ........................... 79 B.7 FT-IR-ATR................................................................................................................. 80 B.7.1 Measurements of Solid Complex Samples.............................................................. 80 B.7.2 FT-IR-ATR Measurements of nanostructured TiO2 films .....................................
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