Singlet fission and triplet-triplet annihilation upconversion are two multiexciton processes intimately related to the dynamic interaction between one high-lying energy singlet and two low-lying energy triplet excitons. Here, we introduce a series of dendritic macromolecules that serve as platform to study the effect of interchromophore interactions on the dynamics of multiexciton generation and decay as a function of dendrimer generation. The dendrimers (generations 1–4) consist of trimethylolpropane core and 2,2-bis(methylol)propionic acid (bis-MPA) dendrons that provide exponential growth of the branches, leading to a corona decorated with pentacenes for SF or anthracenes for TTA-UC. The findings reveal a trend where a few highly ordered sites emerge as the dendrimer generation grows, dominating the multiexciton dynamics, as deduced from optical spectra, and transient absorption spectroscopy. While the dendritic structures enhance TTA-UC at low annihilator concentrations in the largest dendrimers, the paired chromophore interactions induce a broadened and red-shifted excimer emission. In SF dendrimers of higher generations, the triplet dynamics become increasingly dominated by pairwise sites exhibiting strong coupling (Type II), which can be readily distinguished from sites with weaker coupling (Type I) by their spectral dynamics and decay kinetics.
Dendritic architectures by orthogonal thiol-maleimide “click” and furan-maleimide dynamic covalent chemistries
A set of dendrons and dendrimers is synthesized divergently using an orthogonal combination of kinetically-driven thiol-maleimide “click” chemistry and thermodynamically reversible furan-maleimide cycloaddition/retrocycloaddition reactions. Growth is controlled by taking advantage of the selective thiol–ene addition of thiols to the electron withdrawn alkene of maleimide in the presence of electron rich alkene of oxanorbornene. Subsequent activation of growing dendrons/dendrimers requires only heat to induce the dynamic covalent liberation of peripheral furan protecting groups. The methodology introduced provides a new route to multifunctional dendrimers that could, in principle, be synthesized by introducing different branched monomers at any stage of dendrimer growth, allowing dendrimer architectures and properties to be better tailored to their intended applications.
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- Award ID(s):
- 1352239
- PAR ID:
- 10140866
- Date Published:
- Journal Name:
- Organic & Biomolecular Chemistry
- Volume:
- 17
- Issue:
- 34
- ISSN:
- 1477-0520
- Page Range / eLocation ID:
- 7878 to 7883
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
All activities of our daily life, of the nature surrounding us and of the entire society and its complex economic and political systems are affected by stimuli. Therefore, understanding stimuli-responsive principles in nature, biology, society, and in complex synthetic systems is fundamental to natural and life sciences. This invited Perspective attempts to organize, to the best of our knowledge, for the first time the stimuli-responsive principles of supramolecular organizations emerging from self-assembling and self-organizable dendrons, dendrimers, and dendronized polymers. Definitions of stimulus and stimuli from different fields of science are first discussed. Subsequently, we decided that supramolecular organizations of self-assembling and self-organizable dendrons, dendrimers, and dendronized polymers may fit best in the definition of stimuli from biology. After a brief historical introduction to the discovery and development of conventional and self-assembling and self-organizable dendrons, dendrimers, and dendronized polymers, a classification of stimuli-responsible principles as internal- and external-stimuli was made. Due to the enormous amount of literature on conventional dendrons, dendrimers, and dendronized polymers as well as on their self-assembling and self-organizable systems we decided to discuss stimuli-responsive principles only with examples from our laboratory. We apologize to all contributors to dendrimers and to the readers of this Perspective for this space-limited decision. Even after this decision, restrictions to a limited number of examples were required. In spite of this, we expect that this Perspective will provide a new way of thinking about stimuli in all fields of self-organized complex soft matter.more » « less
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Poly(ionic liquid) covalently adaptable networks containing thermoreversible furan–maleimide linkages were prepared and characterized for their thermal, mechanical and conductive properties. Self-healing behaviour was initially evaluated using oscillatory rheology where a G ′/ G ′′ crossover temperature of ∼110 °C was observed. Anhydrous conductivities, as determined by dielectric relaxation spectroscopy, were found to be on the order of 10 −8 S cm −1 at 30 °C. Recovery of >70% of the original stress and strain at break was found within 2 hours at 105 °C as determined from tensile testing experiments, with breakage occurring at a new point on the film. Recovery of conductivity was completed utilizing chronoamperometric cycling whereby >75% of the original current was recovered within two hours at 110 °C.more » « less
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null (Ed.)Poly(ionic liquid) covalently adaptable networks containing thermoreversible furan–maleimide linkages were prepared and characterized for their thermal, mechanical and conductive properties. Self-healing behaviour was initially evaluated using oscillatory rheology where a G′/G′′ crossover temperature of ∼110 °C was observed. Anhydrous conductivities, as determined by dielectric relaxation spectroscopy, were found to be on the order of 10−8 S cm−1 at 30 °C. Recovery of >70% of the original stress and strain at break was found within 2 hours at 105 °C as determined from tensile testing experiments, with breakage occurring at a new point on the film. Recovery of conductivity was completed utilizing chronoamperometric cycling whereby >75% of the original current was recovered within two hours at 110 °C.more » « less
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Clarifying the correlation between the chemical structure of mechanophores and their mechanical reactivity informs the design of mechanochemical systems. One specific correlation that has received much recent attention is that between stereoisomerism and mechanical reactivity. Here, we report previously unobserved differences in the mechanical reactivity of furan–maleimide Diels–Alder (DA) stereoisomers. We evaluated the internal competition between the mechanically triggered retro-DA reaction and the mechanochemical ring opening of gem -dichlorocyclopropane mechanophores in the pulsed sonication of polymer solutions. The relative extent of the two sonomechanochemical reactions in the same polymer shows that the endo DA isomer exhibits greater mechanical lability than its exo isomer. This result contrasts with recent measurements of the relative rates of scission in a similar system and points to potential enhanced sensitivity obtained through the use of internal competition as opposed to absolute rates in assessing mechanical reactivity in sonication studies.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9OB01459D
