2 research outputs found
Studies of polycyclic aromatic hydrocarbon-based organic materials for optoelectronic applications
Ï€-Conjugated polycyclic aromatic hydrocarbons (PAHs) have found increasing
applications in the fields of organic photonics and optoelectronics owing to
their highly tunable photophysical properties, redox activity, and supramolecular
self-assembling behavior. This PhD thesis mainly focuses on the studies of
four classes of PAH-based organic materials, namely diphenyl dibenzofulvenes
(DP-DBFs), pentacenetetraone-derived π-extended tetrathiafulvalene analogues
(TTFAQ-AQ),donor/acceptor(D/A)-functionalized phenanthroimidazoles(PIs),
and bis(diarylmethylene)dihydroanthracenes (Arâ‚„-DHAs).
DP-DBFs have been known to show intriguing crystallization-induced emission
enhancement(CIEE) and aggregation-induced emission (AIE) properties; however,
the molecular origins for them to exhibit such unique photophysical properties have
not yet been clearly reported in the literature. In the first project of this thesis work,
we designed and prepared a series of DP-DBFs with various substituents. With the
aid of solution and solid-state
fluorescence spectroscopic analysis, the AIE and CIEE
properties of DP-DBFs we reinvestigated. Our studies confirmed that the twist angle
around the C=C bond in the DP-DBF is a key factor to control its
fluorescence
behavior.
In the second study, the structure-property relationship of TTFAQ-AQs were
systematically examined. Analyses of their redox properties and electronic band gaps
suggested that they could be promising organic semiconducting materials. Moreover,
the synthesized TTFAQ-AQs featured double curved π-surfaces that contain both
electron-deficient and electron-rich segments. In this way, they can serve as versatile
supramolecular partners to interact with 3-dimensional π-conjugated host molecules
such as fullerenes. A benzo-fused TTFAQ-AQ derivative was observed to form
organized organic co-crystals with electron deficient C₇₀ fullerene through concave-
convex shape complementarity and strong donor-acceptor interactions. The results
point to promising application in redox-active organic electronic materials.
The third project embarked on the design of novel PI-derived organic
chromophores and
fluorophores. PI derivatives containing electron-donating
dithiafulvenyl (DTF) groups and electron-accepting aldehyde groups were synthesized
and characterized in terms of their
fluorescence and electrochemical properties. The
DTF-functionalized PI derivatives were found to show
fluorescence sensitivity to
singlet oxygen through a chemiluminescent mechanism. Moreover, the chemical
oxidative dimerization of DTF end groups led to the construction of a new type
of TTFV-PI macrocycles, which showed interesting
fluorescence turn-on/off behavior
when they interacted with C₆₀ and C₇₀ fullerenes at different ratios. These features
make the synthesized PI materials interesting candidates in the fabrication of efficient
fluorescence sensors for singlet oxygen and fullerenes.
The last project focuses on the synthesis, characterization, and mechanistic
analyses on the photocyclization of a series of Arâ‚„-DHAs. We have made three
different derivatives functionalized with methoxy groups at various positions of the
phenyl ring, a tethered Arâ‚„-DHA derivative as a rigid model compound, and their
photocyclized products. Although the cyclodehydrogenation reaction of this class of
PAHs through the Scholl reaction has been well studied, photocyclization reaction
still lacks sufficient understanding and evidence to support detailed mechanisms. In
our work, it has been observed that the photocyclization only happens on one side of
Arâ‚„-DHA through a two-fold Mallory reaction. To better understand the mechanisms
involved and the molecular reasons behind the two-fold Mallory reaction, we have
utilized experimental and theoretical approaches including X-ray crystallographic
analyses and density functional theory (DFT) calculations. The frontier molecular
orbital (FMO) analyses offered convincing explanation for the regioselectivity of the
two-fold Mallory reaction on a Arâ‚„-DHA. In addition, the importance of the position of
the methoxy substituent on the mechanism of photocyclization has been revealed; in
particular, when the methoxy groups are at the ortho positions, cyclodemethoxylation
occurred instead of cyclodehydrogenation. Collectively, the work in Chapter 5
offers in-depth understanding of the photochemical properties of Arâ‚„-DHAs as well
as valuable guidance for future work on the synthesis of π-extended PAHs and
nanographenes from readilly accessbile Arâ‚„-DHA precursors