A complete series
of experimental and theoretical investigations
on the supramolecular polymerization of chiral (1 and 2) and achiral (3) oligo(phenylene ethynylene)
tricarboxamides (OPE-TAs) is reported. The performance of seargents-and-soldiers
(SaS) and majority rules (MR) experiments has allowed deriving a full
set of thermodynamic parameters, including the helix reversal penalty
(HRP) and the mismatch penalty (MMP). The results described illustrate
the influence exerted by the number of stereogenic centers per monomeric
unit and the temperature on the chiral amplification phenomenon. While
the HRP decreases upon decreasing the number of chiral side chains,
the MMP follows an opposite trend. The experimental trend observed
in MR experiments contrasts with that reported for benzenetricarboxamides
(BTAs), for which the chiral amplification ability increases by lowering
the number of stereogenic centers or increasing the temperature. Theoretical
calculations predict that the rotational angle between adjacent monomeric
units in the stack (ca. 18°) gradually decreases when decreasing
the number of branched chiral side chains and leads to higher MMP
values, in good accord with the experimental trend. The reduction
of the rotational angle gives rise to less efficient H-bonding interactions
between the peripheral amide functional groups and is suggested to
provoke a decrease of the HRP as experimentally observed. In BTAs,
increasing the number of stereogenic centers per monomeric unit results
in a negligible change of the rotation angle between adjacent units
(ca. 65°), and, consequently, the steric bulk increases with
the number of chiral side chains, leading to higher MMP values. The
data presented herein contribute to shed light on the parameters controlling
the transfer and amplification of chirality processes in supramolecular
polymers, highlighting the enormous influence exerted by the size
of the self-assembling unit on the final helical outcome.
Abstract:The article deals with the synthesis and the physical properties of polyaromatic hydrocarbons containing P-atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV-vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in solid state showed that the P-containing PAHs exhibit the expected properties to be used as emitter in WOLEDs.
The tunable luminescent features along with the electrical conductivity (~2 × 10(-4) S m(-1)) exhibited by the gel fibers formed through supramolecular polymerisation of the N-annulated perylenedicarboxamide based π-gelator are reported.
The cooperative supramolecular polymerization of 1 and 2 yields P- or M-type helical aggregates depending on the absolute configuration (S or R) of the stereogenic centres attached to the side chains. The connectivity of the amide group does not affect the handedness of the helical aggregates, but determines a larger cooperativity for retroamides 1.
N-annulated perylenedicarboxamides 1-3 form supramolecular polymers with a strong tendency to aggregate. The bundles of fibers formed generate a spontaneous anisotropy that conditions the chiroptical features of the described molecules in solution; a strong linear dichroism effect accompanies the circular dichroism (CD) outcome. There is no influence of the point chirality existing at the side chains of 1 and 2, and these molecules present the same chiroptical features as achiral 3. Mechanical rotary stirring increases the CD response and the sign of the dichroic signal changes with the stirring direction. Theoretical calculations indicate that the self-assembly of 1-3 in helical columnar stacks generates atropisomers by the restricted rotation of the H-bonded benzamide units. Molecular mechanics/molecular dynamics calculations predict a feasible intrastack stereomutation of the helical aggregates due to the rapid rupture/formation of the amide H-bonds. This oscillating helicity, together with the fact that right- and left-handed helices are predicted to be mostly isoenergetic, justifies the negligible contribution of the molecular chirality embedded in the paraffinic side chains of 1 and 2. The reported CD behavior contributes to shed light on the physical processes promoting flexible macroscopic chirality that, in turn, can be utilized for the spectroscopic visualization of torsional flows generated in a vortex.
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