Date of Award
Fall 2025
Project Type
Dissertation
Program or Major
Chemistry
Degree Name
Doctor of Philosophy
First Advisor
Glen P Miller
Second Advisor
Charles Zercher
Third Advisor
Gonghu Li
Abstract
This thesis addresses the design, synthesis, and functional evaluation of novel π-conjugated organic compounds derived from acene-2,3-dicarbaldehydes with the overarching goal of developing stable and tunable organic semiconductors. An improved one-pot synthesis enabled the efficient preparation of large acene-2,3-dicarbaldehydes like anthracene-2,3-dicarbaldehyde and tetracene-2,3-dicarbaldehyde, both of which exhibit excellent solubility, high photostability and red-shifted absorption spectra. These compounds demonstrate decreasing optical HOMO-LUMO gaps with increasing conjugation length as demonstrated by experimental and computational DFT studies. They are isoelectronic with benchmark semiconductors such as pentacene. Their synthetic utility was demonstrated through transformations into α,α′-diaryl-2,3-acenedimethanols, acenotropones and hydroxyacenotropylium ions. They are converted in one-step to 2,3-diazaacenes via reactions with hydrazine. These heteroacenes and their corresponding N-oxides exhibit decreasing HOMO-LUMO gaps with increasing length and show broadband absorptions and emissions across the visible portion of the electromagnetic spectrum. Their electronic properties and stability profiles suggest potential applications as ambipolar or p-type organic semiconductors. Theoretical (DFT) investigations of isoacenofurans revealed that they inherently possess smaller HOMO-LUMO gaps than isoelectronic acenes, but require steric stabilization to overcome inherent instability. Computational insights guided the synthesis of non-planar, kinetically stabilized isoacenofurans with reduced reactivity. Lastly, halochromic spirocyclic lactones were synthesized that undergo reversible color changes upon exposure to strong acids. The reversible reactions involve formation of highly delocalized trityl cations with strong UV-vis-NIR absorptions.
Together, this work contributes synthetic strategies, structural insights and functional materials that expand the design landscape for organic semiconductors with tailored optoelectronic properties.
Recommended Citation
Liu, Qian, "DESIGN, SYNTHESIS AND CHARACTERIZATION OF SMALL MOLECULE ORGANIC SEMICONDUCTORS WITH TUNABLE ENERGY GAPS" (2025). Doctoral Dissertations. 2958.
https://scholars.unh.edu/dissertation/2958