Author ORCID Identifier

https://orcid.org/0000-0003-0588-8267

Semester

Fall

Date of Graduation

2022

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Carsten Milsmann

Committee Co-Chair

Brian Popp

Committee Member

Brian Popp

Committee Member

Jessica Hoover

Committee Member

Brian Dolinar

Committee Member

Alan Bristow

Abstract

A thorough study of photoluminescent molecules involving the pyridine polypyrrole(ide) ligand platform has been conducted. A detailed analysis on speciation of the proligand H2(MesPDPPh) (H2MesPDPPh = 2,6-bis(5-mesityl-3-phenyl-1H-pyrrol-2-yl)-pyridine) and its dilithium salt Li2(MesPDPPh) revealed temperature- and solvent-dependent effects. These molecules, along with the hydrochloric acid adduct [H3(MesPDPPh)]Cl were found to exhibit short-lived photoluminescence in both tetrahydrofuran and benzene solution. These findings confirm the hypothesis that heavy-atom involvement is crucial for the favorable photophysical properties observed for the Zr(PDP)2 and E(PDP)2 (E = Si, Ge. Sn) families of compounds.

Reactivity studies of H2(MesPDPPh) and its less sterically demanding analogue H2(MePDPPh) were conducted with two different zirconium starting materials containing internal bases. Reaction between H2(MePDPPh) and both ZrBn4 and Zr(NMe2)4 resulted in the corresponding bis-PDP complex Zr(MePDPPh)2 at elevated temperatures. In contrast, only reaction between H2(MesPDPPh) and ZrBn4 gave the desired Zr(MesPDPPh)2, while reaction with Zr(NMe2)4 stopped at the bis-amide complex (MesPDPPh)Zr(NMe2)2. Isolation of the cyclometalated intermediate (cyclo-MesPDPPh)ZrBn highlights the privileged role of ZrBn4 as a starting material in the synthesis of Zr(PDP)2 photosensitizers. This knowledge was utilized for the synthesis of the first bis-PDP hafnium complexes, Hf(R1PDPPh)2 (R1 = Me or Mesityl) which exhibit similar photophysical properties to their zirconium congeners. It is anticipated that the library of (R1PDPPh)MX2 (M = Zr, Hf; X = NMe2, Bn) complexes resulting from this study can be further utilized in the synthesis of heteroleptic group IV photosensitizers.

Ligand modification of H2(MesPDPPh) at the 4-pyridine position and subsequent synthesis of the zirconium complexes provided a new series of photosensitizers. The colors of absorption and emission were found to be tunable over a range of more than 100 nm each, highlighting the excellent control that 4-pyridine substitution holds on the Zr(PDP)2 photophysical properties. Additionally, installation of electron-donating groups skyrocketed the photoluminescence quantum yield to >99% in room-temperature fluid solution, a feat rarely seen for transition metal complexes. These findings prompt the exploration of Zr(PDP)2 photosensitizers in solid-state applications such as organic light-emitting diodes (OLEDs) or solar cells.

Further ligand modification to the pyridine-pyrrolide framework was explored by shifting to the unsubstituted 2,2’-(pyrrolyl)pyridine (HHPMPH) ligand. This allowed for the synthesis of the coordinatively saturated, eight-coordinate Zr(HPMPH)4. The protection of the highly basic Zr-Npyrrolide bonds and increased rigidity resulted in an air- and water-stable complex exhibiting a tremendously long photoluminescence lifetime of nearly 800 μs.

Embargo Reason

Publication Pending

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