Presentation Title

Do bulky ligands induce surface traps on semiconductor nanocrystals?

Faculty Mentor

Ming Lee Tang

Start Date

23-11-2019 8:00 AM

End Date

23-11-2019 8:45 AM

Location

253

Session

poster 1

Type of Presentation

Poster

Subject Area

physical_mathematical_sciences

Abstract

Enhancing the efficiencies of photovoltaics and photocatalysts is a possibility though photon upconversion, a process where the sequential absorption of two or more photons leads to the emission of light at a shorter wavelength that is higher in energy. Combining an organic ligand to an inorganic nanocrystal enhances energy transfer, resulting photon upconversion. Photon upconversion occurs through a process called triplet- triplet annihilation where two molecules, a sensitizer and annihilator, are excited and combine their energies to convert the energy in two photons into one photon of higher energy. This project seeks to identify if intermediates during energy transfer are induced when bulky groups are present on transmitter ligands. This is to test the hypothesis that sterically encumbered transmitter ligands displace existing ligands on nanocrystals, thus forming surface trap states. It was previously seen that compact ligands resulted in direct energy transfer from nanocrystal to molecule. However, once a bulky group is present, an intermediate is formed and the energy is then transferred from the nanocrystal to the intermediate to the molecule. This project is focused on synthesizing tetracene molecules that differ only in their solubilizing groups. Tetracene molecules that bind to nanocrystals with carboxylic acid (-COOH) groups will be functionalized with Triisopropylsilyl (TIPS)-,Triethylsilyl (TES)- and Trimethylsilyl (TMS)- acetylene to further understand why and how bulky groups, such as TIPS-, TES-, and TMS-, induce intermediates, perhaps by removing existing ligands on nanocrystals. All three molecules were synthesized using air-free Schlenk line techniques. Thin-layer chromatography in hexane was used to determine if our desired product was present before running Flash column chromatography to further isolate our target molecules. Then the molecules were characterized by proton Nuclear Magnetic Resonance (NMR) spectroscopy using a Bruker Avance NEO 400.

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Nov 23rd, 8:00 AM Nov 23rd, 8:45 AM

Do bulky ligands induce surface traps on semiconductor nanocrystals?

253

Enhancing the efficiencies of photovoltaics and photocatalysts is a possibility though photon upconversion, a process where the sequential absorption of two or more photons leads to the emission of light at a shorter wavelength that is higher in energy. Combining an organic ligand to an inorganic nanocrystal enhances energy transfer, resulting photon upconversion. Photon upconversion occurs through a process called triplet- triplet annihilation where two molecules, a sensitizer and annihilator, are excited and combine their energies to convert the energy in two photons into one photon of higher energy. This project seeks to identify if intermediates during energy transfer are induced when bulky groups are present on transmitter ligands. This is to test the hypothesis that sterically encumbered transmitter ligands displace existing ligands on nanocrystals, thus forming surface trap states. It was previously seen that compact ligands resulted in direct energy transfer from nanocrystal to molecule. However, once a bulky group is present, an intermediate is formed and the energy is then transferred from the nanocrystal to the intermediate to the molecule. This project is focused on synthesizing tetracene molecules that differ only in their solubilizing groups. Tetracene molecules that bind to nanocrystals with carboxylic acid (-COOH) groups will be functionalized with Triisopropylsilyl (TIPS)-,Triethylsilyl (TES)- and Trimethylsilyl (TMS)- acetylene to further understand why and how bulky groups, such as TIPS-, TES-, and TMS-, induce intermediates, perhaps by removing existing ligands on nanocrystals. All three molecules were synthesized using air-free Schlenk line techniques. Thin-layer chromatography in hexane was used to determine if our desired product was present before running Flash column chromatography to further isolate our target molecules. Then the molecules were characterized by proton Nuclear Magnetic Resonance (NMR) spectroscopy using a Bruker Avance NEO 400.