Computational Study of the Structure, Dynamics, and Photophysical Properties of Conjugated Polymers and Oligomers under Nanoscale Confinement

Abstract

Computational simulations were used to investigate the dynamics and resulting structures of several para-phenylenevinylene (PPV) based polymers and oligomers (PPV, 2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene --> MEH-PPV and 2,5,2',5'-tetrahexyloxy-7,8'-dicyano-p-phenylenevinylene --> CN-PPV). The results show how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution-phase preparation. Secondary structural organization is induced by using the solution-phase structures to generate solvent-free single molecule nanoparticles. Isolation of these single molecule nanostructures from microdroplets of dilute solution results in the formation of electrostatically oriented nanostructures at a glass surface. Our structural modeling suggests that these oriented nanostructures consist of folded PPV conjugated segments with folds occurring at tetrahedral defects (sp3 C-C bonds) within the polymer chain. This picture is supported by detailed experimental fluorescence and scanning probe microscopy studies. We also present results from a fully quantum theoretical treatment of these systems which support the general conclusion of structure-mediated photophysical properties.

Bright conjugated polymer nanoparticles containing a biodegradable shell produced at high yields and with tuneable optical properties by a scalable microfluidic device

“…The backbone rigidity affects the packing order of conjugated polymers and it is influenced both by the conjugated polymer main chain structure and side chains 52 . CN-PPV has a tendency to fold in unfavourable solvents 48 , sharing similar self-assembling 47 47 (see Figure 1 for chemical structures). Consequently, the reduced ability of F8BT to fold during nanoparticle assembly is expected to result in a lower product yield and a larger hydrodynamic diameter compared with CN-PPV (Figure 2 and 3E, respectively).…”

“…The emission spectra of organic molecules depend on environmental characteristics, such as the polarity of the medium, and on the structural features of the macromolecule (for example, its arrangement and the distribution of its chromophores) 7 . Despite the stiff aromatic backbone of the conjugated polymers, the polymer conformation can vary from a relatively opened or coil-like conformation in a good solvent to a more complex morphology in densely packed structures 17,48,60,61 . In solution, the conformation affects the extent of conjugation of a polymer and, accordingly, its optical properties 61 .…”

The effect of the intramolecular properties in single-carrier polymer diodes

“…In order to understand how these molecular alignments relative to the electrodes influence the functioning of polymer diodes, we placed straight conjugated segments (considered as rigid rods) randomly in the gap between two planar electrodes, separated 100 nm from each other (model axis), with their molecular axis parallel, perpendicular or random oriented relative to the electrodes surface. In all the polymer networks built, minimum distances of 0.650 nm were allowed between the polymer strands and between those and the electrodes and the length of each polymer strand was taken from a Gaussian distribution of strand lengths with mean value of 7 monomers, as suggested by previous theoretical and experimental results reported elsewhere [7,8].…”

Stacking of oligo- and polythiophene cations in solution: Surface tension and dielectric saturation

“…The orientation and alignment of polymers in a solid matrix, the formation of aggregates in films and solution, or the ability of organic semiconductors to selfassemble, are the outcome of a complex balance between the spatial features of the molecules and the substrate and the interactions between them at the conditions of synthesis. [1][2][3][4][5][6][7][8][9] By dictating rules for aggregation, these interactions eventually shape properties such as charge delocalization and mobility 2,[9][10][11] or optical 3,[12][13][14] and electromechanical 15 responses. Thiophene-derived oligomers and polymers represent today one of the most promising class of organic semiconductors, finding potential applications in a variety of electronic and electroactive devices.…”

“…5,22 In the present paper, we employ a recently developed first-principles approach to describe the effect of a continuum solvent within the density-functional theory framework 25 and use it to explore the role of polarity and surface tension in the stabilization of dimers of polythiophene and oligothiophene radical cations. Furthermore, we examine the possibility of trimer formation as an intermediate step toward the nucleation of higher-order aggregates and to gain insight on self-assembly in solution.…”