Self‐Assembly Behavior of Diacetylenic Acid Molecules upon Vapor Deposition: Odd–Even Effect on the Film Morphology

Abstract

As eries of linear carboxylic acids containing diacetylenic units at different positions along the chain (C 12 H 25 (C C) 2 (CH 2) n COOH, n = 7-11) werev acuum-deposited on clean silica substrates. The morphologies of the initial films after UV irradiation were studied. Ac lear odd-eveneffect on the morphology of the initial film was observed in that, depending on the spacer length between the diacetylenic unit and carboxyl head group, rings or dendrites of acid dimerl ayers were obtained. Am olecular dynamic simulation of the aggregation process suggests that two competing intermolec-ular interactions and thus aggregation directions are involveda nd modulated by the odd or even carbonc hain length. Further modulation of the interaction by substitution of ap henyl group at the terminus of the chain or by changing the carboxyl head group to an amidobenzoic acidh ead groupl ed to as imilar odd-even effect but with different dimensionso rt rends,w hich can be rationalized similarly. Theser esults give the opportunity to createa lignedc onjugated polymer chainso fd ifferent dimensions throughs elfassemblyfor applicationsinm olecular/organic electronics.

Solvent Polarity-Modulated Molecular Alignment of Linear Diacetylenic Acid Films by Solution Shearing

“…Based on a calculated spacing of ∼46 Å from the out-of-plane GIXD patterns for both PCDA films and the theoretic molecular length of ∼29 Å, a H-bonded dimer-layered structure with an “end-on” orientation but tilted 35–40° from the surface normal and piled head-to-head, tail-to-tail for PCDA molecules in thin films is suggested for all cases. This is similar to that obtained from thermal evaporation …”

“…plane containing the trans zigzag chain (eclipsed conformation), as confirmed by theoretical calculation previously. 21 This is in agreement with the NEXAF data discussed above that the carbonyl vector was parallel to the shearing direction. In contrast, in polar solvents such as chloroform, the major species (at a concentration of 2 mg mL −1 used) were the monomers with the carboxyl group solvated by the solvent molecules, also evidenced in IR spectra.…”

“…This is similar to that obtained from thermal evaporation. 21 Based on the in-plane GIXD profiles of PCDA films from hexane solution, the PCDA molecules formed a 2D quasihexagonal lattice system, with an in-plane spacing of 4.79 Å when the incident beam was parallel to the shearing direction, and distorted spacings at 5.46, 4.75, and 3.89 Å when the incident beam was perpendicular to the shearing direction. A similar phenomenon was observed in the films from chloroform solution, only that the 2D in-plane lattice direction was orthogonal to that in the films from hexane solution.…”

“…Diacetylenic (DA) derivatives are well known for their topochemical polymerization in a crystalline state where the molecules are packed in specific arrangements with the neighboring diacetylenic units tilted at a specific angle and at a specific distance. − The 10,12-pentacosadiynoic acid (PCDA), which has a diacetylenic unit inserted in the center of the long alkyl chain, is known to undergo polymerization in its crystalline state. Aligning these molecules on a substrate, followed by photopolymerization, in principle can generate an oriented poly­(ene-yne) conducting channel, which could be utilized in various electronic applications.…”

A Series of Bisamide‐Substituted Diacetylenes Exhibiting a Terminal Alkyl Odd/Even Parity Effect on Mechanoactivated Photopolymerization

“…The geometric differences at the molecular level have a critical effect on the bulk photopolymerization properties. The initial crystal packing geometries and morphologies of some DA derivatives are known to be determined by the odd/even parity of the alkyl spacers affecting the orientation of hydrogen‐bonded units [23] . Our elaborated results from FTIR, XRD, and X‐ray single‐crystal analysis also provide an understanding of the cooperative effect of amide groups and terminal alkyl chains in DAs on the molecular packing modes.…”