CF₃‐Inspired Synthesis of Air‐Tolerant 9‐Phosphaanthracenes that Feature Fluorescence and Crystalline Polymorphs

Abstract

9-Phosphaanthracene (dibenzo[b,e]phosphorin, acridophosphine) has attracted interest as one of the heavier acenes. Herein, we demonstrate an efficient synthetic process that provides air-tolerant 1,8-bis(trifluoromethyl)-9-phosphaanthracenes. The sterically encumbered and electron-withdrawing trifluoromethyl (CF ) groups are quite advantageous not only to stabilize the intrinsically unstable heavier unsaturated phosphorus atom but also to facilitate construction of the phosphinine skeleton based on a putative increase in aromaticity. The isolated 9-phosphaanthracenes allowed characterization of their fluorescence functionality and planar heteroanthracene frameworks. The crystal structures of 9-phosphaanthracenes are remarkably dependent on the aryl substituents at the 10 position; anthryl-substituted 9-phosphaanthracene showed unique polymorphs that induced different-colored crystals.

A new protocol for the identification of singlet fission sensitizers through computational screening

“…On the other hand, the molecule labeled as 319‐23‐3 corresponds to a thermostable carbazole derivative that crystallizes on a structure similar to the pentacene 53 . In order to cite some drawbacks, the first of them is unstable in the presence of air, and close‐related derivatives had to be designed in order to overcome this issue 54,55 . With respect the second one, low solubility on common organic solvents has been reported 53 …”

Muonium Addition to a peri‐Trifluoromethylated 9‐Phosphaanthracene Producing a High‐Energy Paramagnetic π‐Conjugated Fused Heterocycle

“…Figure 1 indicates the importance of CF 3 for stabilizing the highly reactive P=C double bonds in 9‐phosphaanthracene in a similar manner to protect the reactive molecular parts [9] . The 10‐aryl‐1,8‐bis(trifluoromethyl)‐9‐phosphaanthracenes (Figure 1) were useful for understanding the characters of crystal structure, photo‐emission properties, and crystalline polymorphs [8] …”

“…9‐Phosphaanthracene is one of the heavier congeners of anthracene and has been studied since 1967 [5–7] . Whereas most of the 1,8‐non‐substituted 9‐phosphaanthracenes are labile, we recently established synthesis of air‐tolerant 10‐aryl‐9‐phosphaanthracenes by installing trifluoromethyl (CF 3 ) groups into the peri positions (1,8‐positions) [8] . Figure 1 indicates the importance of CF 3 for stabilizing the highly reactive P=C double bonds in 9‐phosphaanthracene in a similar manner to protect the reactive molecular parts [9] .…”

“…The muon beamline at the TRIUMF cyclotron (M15 beamline) was used, and the Helios spectrometer was equipped. The phosphaanthracene for μSR studies was synthesized according to the protocol described in our previous report [8] …”

From Phosphaphenalenes to Diphosphahexaarenes: An Overview of Linearly Fused Six‐Membered Phosphorus Heterocycles

“…Recently, 30 years after the synthesis of the first phosphaanthracene derivative, Ito, Mikami et al, introduced the trifluoromethyl as electron‐withdrawing group at the 4,5‐positions of an anthracene core bearing a λ 3 ; σ 2 ‐ endo phosphorus center. As a result, the phosphaanthracenes 3 – 5 (Figure ) exhibited an enhanced n ‐type character.…”