Synthesis and Photochemical Characterization of Novel 10-Cyclo Biladiene Derivatives
Date
2024-05
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Photodynamic therapy (PDT) is an alternative cancer treatment which utilizes
a photosensitizer to generate a cytotoxic singlet oxygen species upon light irradiation.
The efficacy of PDT relies heavily upon the photochemical properties of the
photosensitizer, properties which many commercially approved photosensitizers lack.
Subsequently, much work has been done focusing on the development of a
photosensitizer which is capable of strongly absorbing light within the
phototherapeutic window, and which displays a high singlet oxygen quantum yield.
Previous work in the Rosenthal group resulted in the development of Pd[DMBil1], a
compound which has shown great potential as a photosensitizer for PDT. This
compound, however, is unable to strongly absorb light within the phototherapeutic
window, and thus has been the target of modification and functionalization to refine
the spectroscopic and photophysical characteristics of the framework to refine its
properties so that it may be a more potent photosensitizer.
Investigation into the extension of the absorbance profile of the scaffold has
resulted in the substitution of the sp3 hybridized geminal substituents at the 10-
position of the compound with cyclic carbon chains, resulting in a novel family of
cyclobiladiene derivatives, namely Pd[CHBil1], Pd[CPBil1], and Pd[CBBil1]. The
introduction of these groups aims to investigate the impact of incorporating a bulky,
non-electronically active substituent, and to increase the strain on the complex, and
examine the spectroscopic and photophysical characteristics of the resulting
compounds. It was found that the introduction of these groups has drastic impacts on
many of the photochemical properties of the Pd[DMBil1] scaffold, which were
characterized through UV-Vis absorption spectroscopy in order to assess steady-state
spectroscopic characteristics. It was revealed that substitution of the 10-position with
cyclic carbon chains led to an overall decrease in molar absorptivity, coupled with a
slight redshift in absorbance compared to their parent compound, Pd[DMBil1]. In
addition, Pd[CHBil1] exhibited a significantly lower molar absorptivity than
Pd[CBBil1], with a difference of 17,000 M-1 cm-1 at their respective λmax.
Furthermore, when compared to Pd[DMBil1] derivatives with a phenyl-substituted
10-position (Pd[MPBil1] and Pd[DPBil1]), the cyclobiladienes displayed an
increased λmax but a lower molar absorptivity across all wavelengths.
The findings of this study offer valuable insights into the relationship between
structure and photochemical properties of the Pd[DMBil1] scaffold and its potential as
a photosensitizer for PDT. The observed changes in spectroscopic properties upon
substitution at the 10-position contribute to a more well-rounded understanding of the
mechanisms of these compounds. Moreover, the results of this work offer guidance for
the rational design and development of future biladiene-based photosensitizers with
optimized properties for PDT Further studies on the singlet oxygen quantum yield of
these novel Pd[DMBil1] derivatives are warranted to fully assess their potential as
PDT agents.