Highlights on π-systems based on six-membered phosphorus heterocycles

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Rationally designed cationic phospha‐polyaromatic fluorophores were prepared through intramolecular cyclization of the tertiary ortho ‐(acene)phenylene‐phosphines mediated by Cu II triflate. As a result of phosphorus quaternization, heterocyclic phosphonium salts 1 c – 3 c , derived from naphthalene, phenanthrene, and anthracene cores, exhibited very intense blue to green fluorescence ( Φ em =0.38–0.99) and high photostability in aqueous medium. The structure–emission relationship was further investigated by tailoring the electron‐donating functions to the anthracene moiety to give dyes 4 c – 6 c with charge‐transfer character. The latter significantly decreases the emission energy to reach near‐IR region. Thus, the intramolecular phosphacyclization renders an ultra‐wide tuning of fluorescence from 420 nm ( 1 c ) to 780 nm ( 6 c ) in solution, extended to 825 nm for 6 c in the solid state with quantum efficiency of approximately 0.07. The physical behavior of these new dyes was studied spectroscopically, crystallographically, and electrochemically, whereas computational analysis was used to correlate the experimental data with molecular electronic structures. The excellent stability, water solubility, and attractive photophysical characteristics make these phosphonium heterocycles powerful tools in cell imaging.

Section: Introductionmentioning

confidence: 99%

Intramolecular Phosphacyclization: Polyaromatic Phosphonium P‐Heterocycles with Wide‐Tuning Optical Properties

Belyaev

Chen

Liu

et al. 2019

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“…The development of architectures based on p-extended phosphorusheterocyclesisc urrently receiving ag reat deal of attention in the context of liquid crystals, [1] sensors, [2] OLEDs, [3] solar cells, [4] and biomarkers. [5] Particular characteristics of the latter heteroles involve, in most of the cases, [5] electron-accepting properties and aw ide array of accessible post-functionalization reactions at the phosphorus center, which serve to tailor the optoelectronic properties of the p-systems to specific applications. [1][2][3][4][5]6] Probably the most exceptional feature of phosphorus heterocycles,p articularly noted for five-membered phosphorusr ings, phospholes, is their stabilization by hyperconjugation, [5c] which stems from the overlapo ft he s-exocyclic phosphorus bond with the orbitals of the p-fragment.…”

Section: Introductionmentioning

confidence: 99%

“…[5] Particular characteristics of the latter heteroles involve, in most of the cases, [5] electron-accepting properties and aw ide array of accessible post-functionalization reactions at the phosphorus center, which serve to tailor the optoelectronic properties of the p-systems to specific applications. [1][2][3][4][5]6] Probably the most exceptional feature of phosphorus heterocycles,p articularly noted for five-membered phosphorusr ings, phospholes, is their stabilization by hyperconjugation, [5c] which stems from the overlapo ft he s-exocyclic phosphorus bond with the orbitals of the p-fragment. [7] This type of stabilization is very relevant because it is considered to be the origin not only of their particular optoelectronic properties and weak aromaticity [8] but also of their unusual reactivity compared with other main-group element-based heterocy-cles.…”

Section: Introductionmentioning

confidence: 99%

Dismantling the Hyperconjugation of π‐Conjugated Phosphorus Heterocycles

Larrañaga

Romero‐Nieto

Cózar

2019

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The development of π‐extended phosphorus heterocycles has been rapidly increasing because of their unique optoelectronics properties, which are very often considered to be a consequence of special hyperconjugative interactions. However, the latter interactions have primarily been investigated within the five‐membered species, phospholes, and they are often conceptually extrapolated to the rest of π‐extended phosphorus heterocycles (including six‐membered P‐heterocycles) despite evident structural differences. Herein, we report, for the first time, a detailed investigation that sheds light on the hyperconjugative effects of a series of phosphorus heterocyclic systems by means of EDA and NBO calculations within a DFT framework. Our results lay the foundations for the future design of π‐extended phosphorus heterocycles with improved optoelectronics properties.

“…[2,3,[7][8][9][10][11] Importantly,t he introductiono fs ix-memberedp hosphorus heterocycles into the framework of p-extended systemso ften leads to loweringb oth the LUMO and HOMO and thusd ecreasest he chance of oxidative or photodecomposition. [12] In 2018, our group reported the synthesis and optoelectronic properties of novel diphosphahexaarenes. [13] Indeed, the introductiono ft wo six-memberedp hosphorus heterocycles into large linearly fused arenes,i nc ombination with two off-linear benzener ings, led to an outstanding stability and remarkable solubility in common organic solvents.…”

mentioning

confidence: 99%

Phosphorus Post‐Functionalization of Diphosphahexaarenes

Hindenberg

Röminger

Romero‐Nieto

2019

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Diphosphahexaarenes are highly stable π‐extended frameworks containing two six‐membered phosphorus heterocycles that have emerged recently. Herein, we present a detailed investigation on the post‐functionalization reactions of their phosphorus centers with special emphasis on the selectivity of the processes and the impact of the phosphorus functionalizations into the physicochemical properties. These studies reveal that indeed the phosphorus atoms of the diphosphahexaarenes are readily available to be functionalized with quaternizing and oxidizing agents as well as borane groups without compromising the stability of the system. In addition, the optoelectronic properties of the diphosphahexaarenes are impacted by the phosphorus post‐modifications.