Abstract:
The investigation of π-conjugated systems has gained significant attention in recent times due
to the intriguing optoelectronic properties and tunable ground state characteristics. These
systems have a wide range of applications in various fields, such as organic electronics,
spintronics, photovoltaics, and sensors. Understanding the concepts of aromaticity, proaromaticity,
and anti-aromaticity is crucial and has a significant impact on the stability and
ground-state electronic properties of these systems. Chapter 1 presents an introduction to the
background of zethrene and its higher homologues, specifically heptazethrene. The
subsequent discussion is related to indacene- and azulene-embedded polycyclic arenes (PAs)
and polycyclic heteroarenes (PHAs). Based on the aforementioned topics, a series of novel
PAs and PHAs are designed, wherein the heptazethrene, indacene, and azulene cores are
incorporated into the π-backbone.
Higher-order zethrenes exhibit diradical character in the ground state, which can only
be modulated by π-ring annulation, whereas substitution did not affect the electronic ground
state of the zethrene molecules. In Chapter 2, we have shown the isolation of a
dibenzoheptazethrene derivative in the closed-shell ground state bearing push-pull
substituents, which results in a zero diradical character and a low-lying zwitterionic form. In
Chapter 3, attempts were made to isolate highly reactive dicyclopenta[b,d]thiophene (DCPT)
core by fusion of naphthalene and phenanthrene units. However, unexpected decomposition
products were obtained. DCPT is a heteroatom-modified as-indacene in which one of the
central Csp
2−Csp
2 double bonds of the as-indacene unit is replaced with an isoelectronic sulfur
atom. Extending this indacene chemistry to the Chapter 4, we reported a formally aromatic
dicyclopenta[c]fluorenothiophene, which exhibits a dominant antiaromatic character of the
as-indacene subunit due to the inclusion of thiophene unit in the π-backbone. Finally, in
Chapter 5, a tribenzo-extended non-alternat isomer of peri-acenoacene was reported with a
formal azulene unit embedded in the polycyclic backbone, making it the newest nonhexagonal
nanographene accessed through a Scholl-type oxidation approach. All the reported
molecules exhibit remarkable photophysical properties with tunable (anti)aromatic or
diradical characters that make them promising materials for applications in organic
electronics and photonics.