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The Effect of Boron on the Photophysical Properties of Dimetal Quadruply Bonded Complexes

Young, Philip Jordan

Abstract Details

2015, Doctor of Philosophy, Ohio State University, Chemistry.
Research pertaining to renewable energy has increased considerably over the past few decades as the global energy demand rises. The need for new materials capable of efficiently converting solar energy into renewable fuel sources is critical. Additionally, as the world is further industrialized, new sensors and methods for monitoring hazardous waste must also be developed. In designing and optimizing these materials it is necessary to understand the underlying photophysical processes that occur, many of which happen on femtosecond and nanosecond timescales. The advent of femtosecond lasers has led to the development of new techniques capable of observing these ultrafast processes, the results of which will lead to more effective design of new materials. This work focuses on synthesis, characterization, and photophysical properties of M2 quadruply bonded compounds, where M2 = Mo2 or W2. These compounds have broad and intense metal-to-ligand charge transfer (MLCT) absorption bands typically having large extinction coefficients in the range of 20,000-100,000 M-1cm-1, which allows for a great amount of light to be absorbed. Depending on the choice of metal and the extent of p conjugation with the ligands, the MLCT absorption can be modulated in the range of 400-1200 nm. These compounds also have relatively long 1MLCT excited-states compared to other metal complexes, which typically decay to 3M2dd* states and 3MLCT sates, for Mo2 and W2, respectively, making them uniquely suited for studies of excited-state charge distribution. Materials containing both three- and four-coordinate boron moieties have also gained considerable attention in recent years due to their unique properties. Three-coordinate boron behaves much like a carbocation, making it strongly electron withdrawing. The empty 2pz orbital is also capable of extending the p conjugation of organic molecules. Four-coordinate boron enhances the rigidity of organic molecules resulting in intense absorption and fluorescence features. The primary objective of this work was to fuse the interesting properties of M2 compounds with those of boron. The first chapter focuses on tuning the MLCT absorption band of M2 compounds by incorporating three-coordinate boron into the ligand p systems. The vacant pz orbital on the boron atom also permits coordination of fluoride ions which can further tune the absorption band and establish a switch for the MLCT band, resulting in a colorimetric mechanism for fluoride sensing. The following chapters investigate the influence of M2 compounds and four-coordinate boron on the photoisomerization of a derivative of the avobenzone molecule, a common UVA filter used in sunscreens. Typically the tautomerization leads to degradation of the molecule, but the M2 unit introduces a new energy deactivation pathway which drastically reduces decomposition. The conversion between the 1MLCT state to 3MLCT state in the W2 compounds was also investigated with time-resolved infrared spectroscopy. The ability of these compounds to absorb light in a tunable fashion makes them excellent candidates as materials in devices such as solar cells, LEDs, and sensors. The underlying photophysical processes investigated in this work will aid in the development of future materials for solar energy conversion, photocatalysis, and sensing applications.
Malcolm Chisholm (Advisor)
Terry Gustafson (Committee Member)
Claudia Turro (Committee Member)
240 p.

Recommended Citations

Citations

  • Young, P. J. (2015). The Effect of Boron on the Photophysical Properties of Dimetal Quadruply Bonded Complexes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1436355107

    APA Style (7th edition)

  • Young, Philip. The Effect of Boron on the Photophysical Properties of Dimetal Quadruply Bonded Complexes. 2015. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1436355107.

    MLA Style (8th edition)

  • Young, Philip. "The Effect of Boron on the Photophysical Properties of Dimetal Quadruply Bonded Complexes." Doctoral dissertation, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1436355107

    Chicago Manual of Style (17th edition)