To practically use POSS-based hybrids as an optoelectronic materials, influence of the POSS addition on electrical properties of conjugated polymers is essential. Herein, we report the influence on electronic properties and enhanced thermal stability of hybrids composed of conjugated polymers by loading POSS derivatives having dual types of alkyl substituents.
Three types of heterogeneous POSS derivatives with two kinds of alkyl substituents were synthesized, and. The series of measurements for optical and thermal properties and carrier-transport ability revealed that the heterogeneous POSS derivatives can improve thermal stability without critical losses of other properties.
The chemical structures of the materials used in this study are shown in Scheme 1. It was shown from the study with octa-substituted POSS and conjugated polymers that the iso -butyl iC4 and cyclopentyl CP groups on POSS have relatively lower affinity toward conjugated polymers and induced loss of thermal stability, while the octadecyl C18 group can enhance thermal stability of the matrices [ 34 ]. It was assumed that entanglement with polymer chains could disturb molecular motions followed by thermal degradation. From these three alkyl groups, two substituents were introduced into POSS.
Controlling the architectures and optical properties of conjugated polymer aggregates and films
The synthesis of a series of heterogeneous POSS derivatives was performed with the previously established protocol [ 25 ]. It was known that the products used in further analyses included cage mixtures, which are structural isomers and comprise molecular-weight distributions originating from variation of the molar ratios of the two alkyl silane starting materials. PF and P3HT are conventionally used as a carrier-transport layer in organic light-emitting devices and as a traditional donor—acceptor bulk-heterojunction active layer in polymer photovoltaic cells, respectively.
Therefore, enhancement of thermal stability is of great importance for extending device lifetimes. PF and P3HT were prepared via the Yamamoto and oxidation coupling reaction according to the previous methods, respectively Table S1 [ 37 , 38 , 39 ]. For evaluating carrier migration ability, the films were prepared on the ITO electrode via the spin-coating. In Figure S1 , the appearances of the hybrid films are presented. The transparency resulted from compatibility that eliminated heterogeneous POSS crystallization. Heterogeneity and loss of transparency was observed in control samples containing two types of octa-substituted POSS.
Additionally, phase separation and inhomogeneity were hardly detected in nano level in the scanning electron microscopic SEM observations Figure S2. These data represent that POSS fillers can be dispersed in conjugated polymer films with high homogeneity.
Initially, light-absorption properties were investigated with the hybrid films Table 1 and Figures S3—S6. In the PF film, it was known that aggregation at partial polymer chains induces red-shift of the absorption band [ 34 ]. In the previous report, it was demonstrated that POSS derivatives were able to facilitate formation of amorphous state followed by blue-shifted absorption band [ 34 ].
The steric structure of the silica cube could play a critical role in minimizing the crystallization of polymer chains. The spectra indicate that such an effect was realized. By loading POSS into the PF matrices, the absorption bands around nm were sharpened and the apparent absorption maxima were shifted to shorter wavelength region.
It was proposed that polymer chains can form favorable conformation for extending conjugation lengths through the polymer main-chains by releasing structural restrictions caused by inter-chain interaction. In this study, same tendencies were observed. These data support that homogeneous state can be obtained by POSS. Luminescent properties were also examined with the hybrid films Table 1 and Figures S7—S In the PF matrices, significant effects were slightly observed in the spectra and emission efficiencies by adding POSS.
In contrast, large degrees of red-shift were detected in the emission spectra of the P3HT hybrids. Similar to electronic structures in the ground state, main-chain conjugation should be elongated by POSS.
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It was shown that POSS derivatives played a role in improving homogeneity of the polymer matrices. Next, thermal stability of the hybrid films was evaluated with thermogravimetric analysis TGA, Figure 1 and Figure 2.
Degradation temperatures are listed in Table 2. It is likely that thermal motions were induced due to disruption of inter-chain interactions by the rigid POSS cages. It is suggested that entanglement with the dodecyl group and polymer side chains contributed to suppressing molecular motions of polymer chains. Consequently, critical loss of thermal stability could be avoided. Finally, the electric properties of hybrid materials were examined. The carrier mobilities of the hybrid films were evaluated by the time-of-flying TOF experiment in which the transient photocurrent generated with a laser pulse was monitored by an oscilloscope Table S4 [ 40 , 41 , 42 ].
Compared to each pristine polymer, significant changes in the mobility were not observed. Furthermore, the carrier mobilities decreased with an increasing external electrical field with similar extents Figures S12 and S Typically, additives in polymer matrices create carrier traps, followed by critical decreases in carrier mobilities; however, it was revealed that POSS had minimal influence on carrier transport processes through both polymer matrices. According to the previous reports on the conductive composites containing mixed-valence tetrathiafulvalene nanowires, conductivity can be maintained in the bulk materials by gathering nanowires at the surface even in the insulating matrices [ 43 , 44 , 45 , 46 ].
In this study, although POSS could hardly work as a carrier transporter, charges could smoothly pass through homogeneous polymer matrices. This was accomplished by POSS cages controlling the solid-state packing within the hybrid composition. This information on property—structure relationships would be helpful for designing further effective fillers for modulating optoelectronic functions as well as thermal properties of conjugated polymers. In the development of organic opto-electronic devices, reinforcement of durability is still one of big issues to be overcome.
Electronic and Optical Properties of Conjugated Polymers by William Barford - gyqacyxaja.cf
Our concept and materials could be valid to satisfy these demands. Conceptualization, K. National Center for Biotechnology Information , U. Journal List Polymers Basel v. Polymers Basel.
Published online Dec Find articles by Kazuo Tanaka. Find articles by Yoshiki Chujo. Author information Article notes Copyright and License information Disclaimer. Received Nov 20; Accepted Dec This article has been cited by other articles in PMC. Associated Data Supplementary Materials polymerss Abstract Preparation of organic—inorganic hybrids with conventional conjugated polymers such as polyfluorene PF and poly 3-hexylthiophene P3HT were demonstrated via the facile blending in solution by employing polyhedral oligomeric silsesquioxane POSS having heterogeneous alkyl substituents.
Keywords: POSS, hybrid, carrier mobility, thermal stability, conjugated polymer. Introduction By mixing organic molecules and inorganics at the nano level, robust materials, called organic—inorganic hybrids, are created, which have multiple functions originating from both components [ 1 ]. Results and Discussion The chemical structures of the materials used in this study are shown in Scheme 1. Open in a separate window. Figure 1. Figure 2. Scheme 1. Chemical structures of the modified POSS and conjugated polymers used in this study.
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Electronic and Optical Properties of Conjugated Polymers
See provided URL for inquiries about permission. Metadata Show full item record. Abstract The semiconducting properties of conjugated polymers are finding use in various optoelectronic applications, including chemical sensors and light-emitting diodes. In this thesis, we investigate aggregation in conjugated polymers and how it affects the optical properties of these organic materials.
We discuss how aggregation enhances exciton transport properties in fluorescent polymers, thereby increasing the probability of excitons reaching low-energy sites in the polymer. A consequence of this aggregation-enhanced exciton migration is that low-energy defect sites in a conjugated polymer can dramatically alter the polymer's fluorescence properties when it is in an aggregated state. In a poly pphenylene ethynylene PPE that was previously proposed to form green-emitting excimers, we found that a small concentration of anthryl defects in the polymer emitted green fluorescence that was only noticeable when the polymer was in an aggregated state otherwise the polymer was fluorescent blue.
After elucidating the origin of the green fluorescence, we purposely added more emissive anthryl units into the polymer to enhance the blue-to-green fluorescence color change that accompanied polymer aggregation.