[2.2]paracyclophane (pCp), unlike many π-building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self-assembly into extended cofacial π-stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H-bonds), hitherto unstudied in pCps, between pseudo-ortho-positioned amides of a pCp-4,7,12,15-tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H-bonding with π-stacked neighbors. X-ray crystallography confirms the formation of homochiral, one-dimensional pCpTA stacks helically laced with two H-bond strands. The chiral sense is dictated by the planar chirality (R_p or S_p) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.

[2.2]paracyclophane (pCp), unlike many π-building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self-assembly into extended cofacial π-stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H-bonds), hitherto unstudied in pCps, between pseudo-ortho-positioned amides of a pCp-4,7,12,15-tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H-bonding with π-stacked neighbors. X-ray crystallography confirms the formation of homochiral, one-dimensional pCpTA stacks helically laced with two H-bond strands. The chiral sense is dictated by the planar chirality (R_p or S_p) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.

For organic photovoltaic (OPV) cells based on the bulk heterojunction (BHJ) structure, it remains challenging to rationally control the degree of phase separation and percolation within blends of donors and acceptors to secure optimal charge separation and transport. Reported is a bottom-up, supramolecular approach to BHJ OPVs wherein tailored hydrogen bonding (H-bonding) interactions between π-conjugated electron donor molecules encourage formation of vertically aligned donor π-stacks while simultaneously suppressing lateral aggregation; the programmed arrangement facilitates fine mixing with fullerene acceptors and efficient charge transport. The approach is illustrated using conventional linear or branched quaterthiophene donor chromophores outfitted with terminal functional groups that are either capable or incapable of self-complementary H-bonding. When applied to OPVs, the H-bond capable donors yield a twofold enhancement in power conversion efficiency relative to the comparator systems, with a maximum external quantum efficiency of 64%. H-bond promoted assembly results in redshifted absorption (in neat films and donor:C₆₀ blends) and enhanced charge collection efficiency despite disparate donor chromophore structure. Both features positively impact photocurrent and fill factor in OPV devices. Film structural characterization by atomic force microscopy, transmission electron microscopy, and grazing incidence wide angle X-ray scattering reveals a synergistic interplay of lateral H-bonding interactions and vertical π-stacking for directing the favorable morphology of the BHJ.

Three stereochemically pure isomers and two isomeric mixtures of a solution-processable diketopyrrolopyrrole-containing oligothiophene (SMDPPEH) have been used to study the effect of 2-ethylhexyl solubilizing group stereochemistry on the film morphology and bulk heterojunction (BHJ) solar cell characteristics of small molecule organic photovoltaics. The different SMDPPEH stereoisomer compositions exhibit nearly identical optoelectronic properties in the molecularly dissolved state, as well as in amorphous films blended with PCBM. However, for films in which SMDPPEH crystallization is induced by thermal annealing, significant differences in molecular packing between the different stereoisomer formulations are observed. These differences are borne out in photovoltaic device characteristics for which unannealed devices show very similar behavior, while after annealing the RR- and SS-SMDPPEH enantiomers show blue-shifted peak EQE relative to the SMDPPEH isomer mixtures. Unannealed devices made from the most crystalline stereoisomer, meso RS-SMDPPEH, are not completely amorphous, and show improved photocurrent generation as a result. Unlike the other compounds, after thermal annealing the RS-SMDPPEH devices show reduced device performance. The results reveal that the chirality of commonly used 2-ethylhexyl solubilizing chains can have a significant effect on the morphology, absorption, and optimum processing conditions of small molecule organic thin films used as photovoltaic device active layers.

Seven-membered intramolecular hydrogen bonding (7MHB) arrangements involving phenolic hydroxyl group donors have been investigated through Cambridge Structural Database (CSD) and literature mining, and by the characterization of model compounds. The CSD reveals the numerous H-bond accepting functional groups that can participate in 7MHB when they are proximal to a phenolic OH, including alcohols, amides, amines, ethers, N-containing heterocycles, ketones, N-oxides, phosphates, and phosphane oxides. The HB contacts are defined by O_phenol···N and O_phenol···O distances of ca. 2.7 Å, and two dihedral angles that fall within the range of typical peptide γ-turns. Two of the identified 7MHB motifs have been readily mapped onto the phloroglucinol (1,3,5-trihydroxybenzene) scaffold to provide eight model compounds; intramolecular hydrogen bonding involving all three hydroxyl groups is shown to persist in solution and the solid state for the compounds. Intramolecular 7MHB enforces nonplanar conformations that should be useful when designing molecular hosts and catalysts.

Reported are the syntheses of ester-functionalized (6–8) and alkyl-substituted (9) 1-aza-adamantanones; the easy handling of the compounds provides an opportunity to comprehensively study the fundamental changes in structure and reactivity that can accompany the donor–acceptor arrangement in rigid β-aminoketones. X-ray structural analysis of trione 6 and dione 7 reveals bond length and angle variations consistent with through-bond (hyperconjugative) donor–acceptor interactions. Observed is a shortening of the CN bond, elongation of the central CC bond (to ≈1.6 Å), and a significant pyramidalization of the carbonyl carbon within the donor–σ-acceptor pathway. UV/Vis spectra of 6–9 show a new absorption maximum (λ_max=260–275 nm in three solvents), the so-called “σ-coupled transition”; the molar absorptivity scales with the number of carbonyl groups (for trione 6, ε ≈3000, for dione 7, ε ≈2000) and the band reversibly disappears upon addition of acid. IR and ¹³C NMR spectroscopic data show trends consistent with through-bond donation to the carbonyl acceptor groups and commensurate weakening of the carbonyl π bond. High yielding acid-mediated fragmentations are used to illustrate the effects of the donor–acceptor arrangement on the reactivity of the molecules. Given that donor–σ-acceptor molecules have recently been found to show self-assembly behavior and macromolecular properties linked to their unusual structure, the current analysis encourages further consideration of the systems in advanced materials applications.