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A series of simple ditopic hydrogen-bonding-capable molecules functionalized with 2,4-diamino-1,3,5-triazine (DAT), barbiturate (B), and phthalhydrazide (PH) on both termini of a 2,2′-bithiophene linker were designed and synthesized. The intrinsic electronic structures of the ditopic DAT, PH, and B molecules were investigated with ground-state density functional theory calculations. Their solution absorbance was investigated with UV-vis, where it was found that increasing size of R group substituents on the bithiophene linker resulted in a general blue-shift in solution absorbance maximum. The solid-state optical properties of ditopic DAT and B thin films were evaluated by UV-vis, and it was found that the solid-state absorbance was red-shifted with respect to solution absorbance in all cases. The three DAT molecules were vacuum-thermal-deposited onto Au(111) substrates and the morphologies were examined using scanning tunneling microscopy. (DAT-T)2 was observed to organize into six-membered rosettes on the surface, whereas (DAT-TMe)2 formed linear assemblies before and after thermal annealing. For (DAT-Toct)2 , an irregular arrangement was observed, while (B-TMe)2 showed several co-existent assembly patterns. The work presented here provides fundamental molecular–supramolecular relationships useful for semiconductive materials design based on ditopic hydrogen-bonding-capable building blocks. 

The iterative association of monomer units through noncovalent interactions often leads to chiral supramolecular polymers. Monomers comprising these materials can be further divided into those with chiral centers and those without. The latter class is often less studied but attractive since it features monomer designs with chirality at the core rather than the periphery of the molecules. In this mini‐review, we summarize the existing strategies to construct supramolecular polymers from chiral molecules with no chiral centers and offer perspectives on fundamental trends and differences between them and their counterparts with chiral centers. © 2020 Society of Industrial Chemistry

 

π-Conjugated oligomers functionalized with the popular dicyanorhodanine (RCN) electron acceptor are shown to be susceptible to photo-induced Z / E isomerization. The stereochemistry of two model RCN-functionalized thiophenes is confirmed by single crystal X-ray analysis and 2D NMR, and shown to be the thermodynamically stable Z form. Relative energies, Z / E configurations, and conformational preferences are modelled using density functional theory (DFT). The photophysical properties of the model compounds are explored experimentally and computationally; the Z and E isomers display similar absorption profiles with significant spectral overlap and are inseparable upon irradiation to a photostationary state. The well-behaved photoisomerization process is routinely observable by thin-layer chromatography, UV-vis, and NMR, and the photochemical behavior of the two RCN-functionalized thiophenes is characterized under varying wavelengths of irradiation. Ultraviolet (254 nm) irradiation results in photostationary state compositions of 56/44 and 69/31 Z -isomer/ E­ -isomer for substrates functionalized with one thiophene and two thiophenes, respectively. Ambient laboratory lighting results in excess of 10 percent E -isomer for each species in solution, an important consideration for processing such materials, particularly for organic photovoltaic applications. In addition, a photoswitching experiment is conducted to demonstrate the reversible nature of the photoreaction, where little evidence of fatigue is observed over numerous switching cycles. Overall, this work showcases an approach to characterize the stereochemistry and photochemical behavior of dicyanorhodanine-functionalized thiophenes, widely used components of functional molecules and materials. 

Reported here is the design and synthesis of among the first pyridine terminated acceptor–donor–acceptor–donor–acceptor (A–D–A–D–A) based π-conjugated oligomers, EH_DPP_2T_Pyr ( 1 ), EH_II_2T_Pyr ( 2 ), and EH_II_1T_Pyr ( 3 ). The molecules incorporate thiophenes as electron donors, isoindigo/diketopyrrolopyrrole as electron acceptors, and are capped with pyridine, a weak electron acceptor, on both ends. All target oligomers show attractive photophysical properties, broad absorption in the visible region ( λ max = 636 nm, 575 nm, and 555 nm, for 1 , 2 , and 3 , respectively) and emission which extends to the IR region (emission λ max = 734 nm and 724 for 1 and 2 , respectively). Given the pyridine nitrogens, the optoelectronic properties of the compounds can be further tuned by protonation/metalation. All compounds show a bathochromic shift in visible absorption and fluorescence quenching upon addition of trifluoroacetic acid (TFA). Similar phenomena are observed upon addition of metals with a particularly strong response to Cu 2+ and Pd 2+ as indicated by Stern–Volmer analysis ( e.g. , for Pd 2+ ; K sv = 7.2 × 10 4 M −1 ( λ = 673 nm), 8.5 × 10 4 M −1 ( λ = 500 nm), and 1.1 × 10 5 ( λ = 425 nm) for 1 , 2 , and 3 , respectively). The selective association of the molecules to Cu 2+ and Pd 2+ is further evidenced by a color change easily observed by eye and under UV light, important for potential use in colorimetric sensing. 

Reported here is the synthesis and self‐assembly characterization of [n.n]paracyclophanes ([n.n]pCps,n=2, 3) equipped with anilide hydrogen bonding units. These molecules differ from previous self‐assembling [n.n]paracyclophanes ([n.n]pCps) in the connectivity of their amide hydrogen bonding units (C‐centered/carboxamide vs.N‐centered/anilide). This subtle change results in a ≈30‐fold increase in the elongation constant for the[2.2]pCp‐4,7,12,15‐tetraanilide ([2.2]pCpNTA) compared to previously reported[2.2]pCp‐4,7,12,15‐tetracarboxamide ([2.2]pCpTA), and a ≈300‐fold increase in the elongation constant for the[3.3]pCp‐5,8,14,17‐tetraanilide ([3.3]pCpNTA) compared to previously reported[3.3]pCp‐5,8,14,17‐tetracarboxamide ([3.3]pCpTA). The[n.n]pCpNTAmonomers also represent the reversal of a previously reported trend in solution‐phase assembly strength when comparing[2.2]pCpTAand[3.3]pCpTAmonomers. The origins of the assembly differences are geometric changes in the association between[n.n]pCpNTAmonomers—revealed by computations and X‐ray crystallography—resulting in a more favorable slipped stacking of the intermolecular π‐surfaces ([n.n]pCpNTAvs.[n.n]pCpTA), and a more complementary H‐bonding geometry ([3.3]pCpNTAvs.[2.2]pCpNTA).