An official website of the United States government
Multiple reviews have been written concerning conjugated macromonomers and polymers both as general descriptions and for specific applications. In most examples, conjugation occurs via electronic communication via continuous overlap of π orbitals, most often on carbon. These systems can be considered to offer traditional forms of conjugation. In this review, we attempt to survey macromonomers and polymers that offer conjugation involving novel forms of carbon and/or other elements but with conjugation achieved via other bonding formats, including many where the mechanism(s) whereby such behavior is observed remain unresolved. In particular, this review emphasizes silsesquioxane containing polymeric materials that offer properties found typically in conjugated polymers. However, conjugation in these polymers appears to occur via saturated siloxane bonds within monomeric units that make up a variety of polymer systems. Multiple photophysical analytical methods are used as a means to demonstrate conjugation in systems where traditional conjugation is not apparent.
more »
« less
This content will become publicly available on January 1, 2026
Torsional influences on cross‐conjugated thieno[3,4‐ b ]thiophene photochromes
Abstract Photoresponsive conjugated polymers are a promising target for modern organic electronics. Numerous photoswitchable repeat units have been included covalently within polymeric structures to enable responsive chromic materials, most commonly through side‐chain appendages or through formal conjugation along a π‐conjugated backbone. We recently disclosed a new design whereby the photoswitch elements are cross conjugated to a conjugated polymer main chain. In this case, we found that the extent of photoconversion was dictated in part by competitive main chain light absorption, which could be suppressed by using a photoswitching motif that carried most of the frontier molecular orbital densities. Here, we report the modeling and synthesis of a series of thieno[3,4‐b]thiophene (TT)‐based photochromes with various aromatic flankers imparting varying degrees of steric bulk and π‐conjugation in order to elucidate the balancing act between steric and electronic factors to promote photochromism. These model systems provide a better understanding of the behavior of photochromic units within extended oligomeric and polymeric π‐conjugated materials.
more »
« less
- Award ID(s):
- 2305009
- PAR ID:
- 10608946
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Physical Organic Chemistry
- Volume:
- 38
- Issue:
- 1
- ISSN:
- 0894-3230
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Mechanically deformable polymeric semiconductors are a key material for fabricating flexible organic thin‐film transistors (FOTFTs)—the building block of electronic circuits and wearable electronic devices. However, for many π‐conjugated polymers achieving mechanical deformability and efficient charge transport remains challenging. Here the effects of polymer backbone bending stiffness and film microstructure on mechanical flexibility and charge transport are investigated via experimental and computational methods for a series of electron‐transporting naphthalene diimide (NDI) polymers having differing extents of π‐conjugation. The results show that replacing increasing amounts of the π‐conjugated comonomer dithienylvinylene (TVT) with the π‐nonconjugated comonomer dithienylethane (TET) in the backbone of the fully π‐conjugated polymeric semiconductor, PNDI‐TVT100(yielding polymeric series PNDI‐TVTx, 100 ≥x≥ 0), lowers backbone rigidity, degree of texturing, and π–π stacking interactions between NDI moieties. Importantly, this comonomer substitution increases the mechanical robustness of PNDI‐TVTxwhile retaining efficient charge transport. Thus, reducing the TVT content of PNDI‐TVTxsuppresses film crack formation and dramatically stabilizes the field‐effect electron mobility upon bending (e.g., 2 mm over 2000 bending cycles). This work provides a route to tune π–π stacking in π‐conjugated polymers while simultaneously promoting mechanical flexibility and retaining good carrier mobility in FOTFTs.more » « less
-
Abstract The extension of conjugated organoboranes from monomeric species to oligomers, macrocycles, and polymers offers access to a plethora of fascinating new materials. The p–π* conjugation between empty orbitals on boron and the conjugated linkers not only affects the electronic structure and optical properties, but also enables mutual interactions between electron‐deficient boron centers. The unique properties of these electron‐deficient π‐conjugated systems are exploited in highly luminescent materials, organic optoelectronic devices, and sensing applications.more » « less
-
Abstract Reactions oftrans‐(C6F5)(p‐tol3P)2Pt(C≡C)nSiEt3(PtC2nSi;n=5, 7, 9) and excessPtClin the presence of wetn‐Bu4N+F−(to effect protodesilylation) under Sonogashira‐type conditions (CuCl, base, other additives) afford the title compoundsPtC10Pt,PtC14Pt, andPtC18Ptin 42–32 % yields. A four‐fold substitution of the phosphine ligands inPtC10Ptby PEt3affordsPt'C10Pt’(78 %), and a Sonogashira reaction ofPt'C2HandPt'ClaffordsPt'C2Pt’(68 %). The analogous reaction withPtC2SiandPtClis unsuccessful, presumably for steric reasons. The crystal structures ofPtC10Pt,PtC14Pt,Pt'C10Pt′, andPt'C2Pt’exhibit a number of interesting trends and features. Certain sp chain extension reactions that lead to or employ the precursorsPtC10Si,PtC12Si,PtC14Si, andPtC18Sisometimes give byproducts derived from C2loss, and possible origins are discussed. Related phenomena have been reported by others in the course of synthesizing extended conjugated polyynes.more » « less
-
Abstract A series of largely π‐extended multichromophoric molecules including cross‐conjugated, half cross‐conjugated, conjugation‐interrupted and linearly conjugated systems were synthesized and characterized. These multichromophoric molecular systems revealed interesting structural‐property relationships. Bisporphyrin‐fused pentacenesPen‐1 bandPen‐2 ashowed rich redox chemistry with 7 and 8 observable redox states, respectively. The linearly‐conjugated bisporphyrin‐fused pentacenes (Pen‐1 bandPen‐2 a) possess much narrower HOMO–LUMO gaps (1.65 and 1.42 eV redox, respectively) and higher HOMO energy levels than those of their pentacene analogues (2.23 and 2.01 eV redox, respectively), similar to those of much less stable hexacenes and heptacenes. An estimated half‐life of >945 h was obtained for bisporphyrin‐fused pentacenePen‐2 a, which is much longer than that of its pentacene analogue (BPE‐P, half‐life, 33 h).more » « less
