11 research outputs found
Singlet-triplet energy gaps modulation of Diindeno [1,2-b: 1’2’-g] anthracene molecular family
Nowadays there is a large interest in organic materials based on diradical polycyclic aromatic hydrocarbons (PAHs) due to their unique properties, such as narrow frontier-orbital energy gaps, strong absorption in the visible spectrum, etc. However, the inherent diradical nature make these compounds with limited chemical stability giving rise to rapid decomposition under ambient conditions thus reducing their practical use. In recent years PAH diradicals that exhibit remarkable stability have been prepared thanks to the description of efficient synthetic routes to access them. One of these remarkable cases is the diindeno [1,2-b: 1’2’-g] anthracene, named as DIAn. DIAn is constituted by antiaromatic segments together with a central pro-aromatic structure.
One of the important observable properties of diradicals is the singlet-triplet energy gap, ∆EST, which is intimately connected with the diradical character. The possibility of access to the molecular structure of diradicals is very valuable since properties such as the bond-order or the bond-length alternation of the mentioned moieties reveal the diradical content. Electronic and vibrational spectroscopies are alternative sources of structural information that often compensate the absence of solid-state structures.
In this communication, we expand the studies of DIAn by introducing another aspect of the modulation of the ∆EST which concerns with: i) the extension of the terminal benzenes with another fused benzene (i.e., forming terminal napthalenes) and ii) with the isomerization resulting from the fusion topology of these terminal benzenes. We will present a UV-Vis-NIR and Raman spectroscopic study of the new compounds. The variation of the spectra within molecular family will be discussed in connection with the variation of ∆EST and with the diradical character of the new molecules.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
A Biradical Balancing Act: Redox Amphoterism in a Diindenoanthracene Derivative Results from Quinoidal Acceptor and Aromatic Donor Motifs
The
reduced and oxidized states of an open-shell diindenoÂ[<i>b,i</i>]Âanthracene (<b>DIAn</b>) derivative have been
investigated by experimental and theoretical techniques. As a result
of moderate biradical character and the ability of cyclopenta-fused
scaffolds to stabilize both positive and negative charges, <b>DIAn</b> exhibits rich redox chemistry with four observable and isolable
charged states. Structural and electronic properties of the <b>DIAn</b> system are brought to light by UV–vis–NIR
and Raman spectroelectrochemical measurements. Aromatization of the
diindeno-fused anthracene core upon successive single-electron injections
is revealed through single-crystal X-ray diffraction of radical anion
and dianion salts. We present a rare case where the pseudoaromatic/quinoidal
ground state of a neutral biradical polycyclic hydrocarbon leads to
a stable cascade of five redox states. Our detailed investigation
of the transformation of molecular structure along all four redox
events provides a clearer understanding of the nature of charge carriers
in ambipolar organic field-effect transistors
Expanded Indacene-Tetrathiafulvalene Scaffolds:Structural Implications for Redox Properties and Association Behavior
Alkyl Phosphite Inhibitors for Frontal Ring-Opening Metathesis Polymerization Greatly Increase Pot Life
Frontal ring-opening metathesis polymerization
(FROMP) has potential
for use in rapid fabrication of structural polymers. However, the
high activity of the ruthenium catalyst used for FROMP has limited
the working time to <1 h. We report the use of alkyl phosphites
as inhibitors for Grubbs’ type catalysts to substantially extend
working time. Subtle changes in alkyl phosphite structure are shown
to impact both pot life and frontal velocity. Specifically, by varying
phosphite structure and concentration, we are able to control pot
life between 0.25 and 30 h while still allowing FROMP to proceed at
velocities between 1 and 8 cm/min to yield fully cured thermoset polymers.
These results are of interest for conventional ROMP synthesis and
may open the way to new FROMP-based manufacturing possibilities