Effect of the Solvent on the Conformation of Isolated MEH‐PPV Chains Intercalated Into SnS₂

Abstract

Photophysical processes in conjugated polymers are influenced by two competing effects: the extent of excited state delocalization along a chain, and the electronic interaction between chains. Experimentally, it is often difficult to separate the two because both are controlled by chain conformation. Here we demonstrate that it is possible to modify intra-chain delocalization without inducing inter-chain interactions by intercalating polymer monolayers between the sheets of an inorganic layered matrix. The red-emitting conjugated polymer, MEH-PPV, is confined to the interlayer space of layered SnS(2). The formation of isolated polymer monolayers between the SnS(2) sheets is confirmed by X-ray diffraction measurements. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of the incorporated MEH-PPV chains reveal that the morphology of the incorporated chains can be varied through the choice of solvent used for chain intercalation. Incorporation from chloroform results in more extended conformations compared to intercalation from xylene. Even highly twisted conformations can be achieved when the incorporation occurs from a methanol:chloroform mixture. The PL spectra of the MEH-PPV incorporated SnS(2) nanocomposites using the different solvents are in good agreement with the PL spectra of the same solutions, indicating that the conformation of the polymer chains in the solutions is retained upon intercalation into the inorganic host. Therefore, intercalation of conjugated polymer chains into layered hosts enables the study of intra-chain photophysical processes as a function of chain conformation.

Decoupling 2D Inter‐ and Intrachain Energy Transfer in Conjugated Polymers

“…The film patterns of SnS 2 restacked with the different polymers all show an intense reflection at 5.8 (2 q = 15.48), corresponding to the caxis interlayer spacing of SnS 2 single crystals, [37] and an additional peak at 11 (2 q = 8.58), corresponding to the (001) reflection of polymer-incorporated SnS 2 . The expansion of the interlayer spacing by about 5 to accommodate the polymer guest species is in good agreement with the c-axis expansion observed for the intercalation of polyaniline, [38] polyfluorene, [15] or poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] [36] monolayers into layered hosts. The ratio of the intensity of the peak at 8.58 to that at 15.48 in all patterns shown in Figure 2 is about 0.25 and implies that about a quarter of the layers in each of the samples are intercalated with polymer.…”

“…[35] To study 2D energy transfer in conjugated polymers, PF and PF with 1, 2, or 5 mol % fluorenone defects were separately incorporated into layered SnS 2 by the procedure recently reported for incorporation of conjugated polymers into inorganic layered compounds. [15,36] In this process, Li atoms are intercalated into the interlayer galleries of SnS 2 , followed by exfoliation of Li x SnS 2 to form a suspension of SnS 2 single layers. Restacking the SnS 2 layers in the presence of the conjugated polymers effectively encapsulates the polymer chains between two adjacent SnS 2 layers.…”

Watching the Annealing Process One Polymer Chain at a Time

“…Ensemble spectroscopic measurements have shown that CP chains in the solvents used here are isolated, well solvated, and contain few, if any, intra-chain contacts. [18][19][20] In a spin-coated MEH-PPV/PMMA film, SMS data show a heterogeneous distribution of collapsed CP chain conformations, including subpopulations of relatively disordered conformations that are kinetically trapped in a high energy state and ordered conformations with a low energy state. During SVA, the film resides in a heterogeneous mixture of solid and liquidlike phase in which the CP chains undergo folding/unfolding events between a collapsed and an extended conformation.…”

Solvent Vapor Annealing of Single Conjugated Polymer Chains: Building Organic Optoelectronic Materials from the Bottom Up

“…On the one hand, conjugated polymers have enormous technological potential as low-cost, easily processed materials open to a diverse set of applications, including biomedical sensors, inexpensive solar cells, light-emitting diodes, and printable electronics. − On the other hand, solution-processing methods are highly complex at the molecular level, which prevents the development of rational design approaches to improve these methods. During processing, conjugated polymers are first dissolved in a suitable solvent, in which they can form a random coil structure with few, if any, inter- and intrachain contacts. − Second, the material is processed by different methods, for example, doctor-blading, , drop-casting, or spin-casting, , and the conjugated polymers form a neat solid film during the evaporation of the solvent. The film morphology is mainly determined by the second step and depends on a variety of parameters, such as solvent quality, evaporation rate, and substrate surface .…”