Closely Stacked Oligo(phenylene ethynylene)s: Effect of π-Stacking on the Electronic Properties of Conjugated Chromophores

Abstract

In this work, a bicyclo[4.4.1]undecane scaffold is used to hold oligo(phenylene ethynylene) units in a cofacially stacked arrangement along the entire length of the conjugated units. We study the impact that the resulting strong interchain interactions have on the photophysical properties. The length of the individual oligomer branches was varied from three to five rings to investigate the effect of conjugation on the electronic properties of the stacked segments. Absorption and fluorescence spectra were recorded and compared to those of the corresponding unstacked analogues. Time-dependent density functional theory calculations were carried out and helped to rationalize the low-energy features present in the fluorescence spectra of the stacked systems. The calculations indicate that the low-energy emissions are due to the presence of excimer-like states. The stronger intensity of the low-energy fluorescence band observed in the five-ring stacked system compared to the three-ring analogue is attributed to the smaller activation barrier that separates the local intrachain state and the excimer-like state in the former compound.

π-Conjugated polymer-layered structures: synthesis and self-assembly

“…24,25 Among the different types of linkers, hairpin-shaped rigid linkers can promote the formation of intramolecular π-stacked structures. [26][27][28][29][30] We have recently reported the synthesis of polymers with layered aromatic rings using a xanthene scaffold as a hairpin-shaped linker; these polymers exhibit intramolecular π-stacked structures with multiple aromatic rings stacked along a single polymer chain. [31][32][33][34][35][36] They can be regarded as the assembly of several small π-conjugated units.…”

4,5-Dimethylbenzene-1,2-dimethanol

“…Analysis of our process indicated that the entire sequence to produce 13.6 g of 1 could be carried out in three days at a cost that is significantly less than that of the commercial material. The conversion of this diol to 6,7-dimethylphthalazine has been previously reported [13]. (1) In a 250-mL, heavy-walled, round-bottomed pressure vessel (CHEMGLASS CG-1880-R-03) equipped with a magnetic stirrer was placed 2,3-dimethyl-1,3-butadiene (2, 10.0 g, 121.7 mmol), dimethyl acetylenedicarboxylate (3, 17.3 g, 121.7 mmol) and toluene (70 mL).…”

Synthesis of Highly Distorted π‐Extended [2.2]Metacyclophanes by Intermolecular Double Oxidative Coupling

“…Compared to the monomer 6, the lowest-energy absorption bands of the dimers 2 are bathochromically shifted, suggesting narrowing of the HOMO-LUMO gap owing to throughspace interaction. [24] Interestingly, the red-shifts in the dimers 2 c, 2 b, and 2 a becomes smaller in this order, indicating that the distortion weakens the through-space interaction between two p-systems. The similar feature is also observed for pextended derivative 5.…”