π‐Stacked Oligo(phenylene vinylene)s Based on Pseudo‐Geminal Substituted [2.2]Paracyclophanes: Impact of Interchain Geometry and Interactions on the Electronic Properties

Abstract

The design of conjugated organic semiconducting materials for use in field-effect transistors, light-emitting diodes, and solar cells requires a detailed understanding of the relationships between molecular geometry, interchain interactions, and electronic properties. [1] The investigation of molecules that consist of pairs of stacked conjugated chains held in welldefined arrangements by a [2.2]paracyclophane (CP) [2] core is a useful strategy to explore interactions between p systems. For example, Bazan et al. have performed extensive spectroscopic and theoretical analyses of stacked phenylene vinylenes (PV) based on pseudo-para (pp) analogues of [2.2]paracyclophane. [3] When two stilbene segments (PV 2 ) are stacked in this fashion, that is, pp-CP(PV 2 ) 2 in Figure 1, the fluorescence spectrum is dominated by a broad featureless peak that is significantly red-shifted from the absorption maximum by virtue of the presence of a localized "phane state". [3] However, the fluorescence spectrum of the analogue with longer stacked 1,4-distyrylbenzene (PV 3 ) segments, that is, pp-CP-(PV 3 ) 2 , resembles that of the corresponding unstacked conjugated oligomer (Me 2 PV 3 ). While the pp and pseudo-ortho (po) analogues hold the two conjugated chains in close proximity, only the phenylene rings within the paracyclophane core are stacked. As a result, there are minimal interactions between the two conjugated segments as soon as their lengths are increased.The pseudo-geminal (pg) substitution pattern of [2.2]paracyclophane holds substituents on each ring directly atop one another. Such stacking of conjugated units leads to facile intramolecular photochemical cycloadditions, [4][5][6][7] and new electronic transitions in multi-decker stacks. [8] The opportunity to prepare new materials containing the cyclophane core has recently attracted increased attention. [9,10] Here, we explore the absorption and fluorescence spectra of stacked PV oligomers that are based on the pg-CP core: the stacked stilbene pg-CP(PV 2 ) 2 and the analogoues distyrylbenzene, pg-CP(PV 3 ) 2 . We compare the spectroscopic and electronic properties of the pg compounds to those of their pp and po analogues and the corresponding isolated oligomers.Conjugated arms were installed on the pg core by a Heck reaction between 4,15-divinyl[2.2]paracyclophane [5] and 1iodobenzene or 1-iodo-4-styrylbenzene to afford pg-CP[PV 2 ] 2 and pg-CP[PV 3 ] 2

Multichannel Conductance of Folded Single‐Molecule Wires Aided by Through‐Space Conjugation

“…For example, f-TPE-PPy shows amost significant absorption band peaking at 282 nm, and alow-energy absorption tail, which is similar to paracyclophanes. [22,23] However,t he absorption spectrum of l-TPE-PPy is strongly red-shifted, with am ain absorption peak at 301 nm and as houlder at 342 nm. In general, the origins of short-and long-wavelength absorption bands are associated to the transitions from ground (S 0 )state to second (S 2 )and first (S 1 )excited states,respectively.…”

“…Thee xtremely large Stokes shifts of 203 and 165 nm for f-TPE-PPy and f-TPE-PEPy further evidence their weak through-bond conjugation but efficient through-space conjugation. [22,23] Since the folded molecules are much more rigid than the linear counterparts, [25] their PL efficiencies are greatly enhanced in solutions (Table 1), owing to the suppression of intramolecular motions.…”

Einfluss der Plattendicke auf die Kontaktzeit beim elastischen Stoßvorgang

“…The smallest glycine residue adjacent to the OPV core (DFAG) led to nanostructures with broad and featureless redshifted luminescence with a longer excited‐state lifetime (7.53 ns) relative to the molecular structure, while the largest valine and isoleucine residues (DFAV, DFAI) led to well‐structured vibronic emission with much shorter excited‐state lifetimes (DFAV had a biexponential decay of 0.86 (0.25) and 0.40 ns (0.75)). These are two very distinct excited‐state outcomes that we have assigned to be excimeric and excitonic in nature, respectively, based on comparison to prior experimental and theoretical analyses of related chromophores and assemblies 20,23,24. To support this duality, it is instructive to note that the alanine residue (DFAA) revealed a noticeable superposition of both outcomes, and as such had substantial components of both the short‐ and long‐lived excited‐state species observed in the time‐resolved emission decay (1.00 (0.86) and 4.02 ns (0.32)).…”

Peptide Nanostructures with π‐Ways: Photophysical Consequences of Peptide/π‐Electron Molecular Self‐Assembly

“…These are two very distinct excitedstate outcomes that we have assigned to be excimeric and excitonic in nature, respectively, based on comparison to prior experimental and theoretical analyses of related chromophores and assemblies. [20,23,24] To support this duality, it is instructive to note that the alanine residue (DFAA) revealed a noticeable superposition of both outcomes, and as such had substantial components of both the short-and long-lived excited-state species observed in the time-resolved emission decay (1.00 (0.86) and 4.02 ns (0.32)).…”