Structural, Photophysical, and Conductive Properties of n-Hexyl Substituted Hybrid Polysilylene−Polysilyne Networks

Abstract

Structural, photophysical, and charge transport properties of n-hexyl substituted polysilylenes containing 5, 33 or 67% n-hexylsilyne branching points were investigated. According to WAXD, DSC, and vibrational studies, introduction of branching points partially reduces the high degree of crystallinity of linear poly(di-n-hexylsilylene). A thermal transition occurs in all polymers, which leads to solid state thermochromic behavior. Solution thermochromism is also observed. It is shown that in the partially branched polymers the narrow band gap of polysilynes is accompanied by an exciton delocalization approaching that of linear polysilylenes. In the solid state, charge carrier mobilities, determined with the pulse-radiolysis time-resolved microwave conductivity technique, are high but decrease with increasing branching. They range from 1.5 × 10-5 for the linear polymer to 7.6 × 10-7 m2 V-1 s-1 for the polymer with 67% branching sites. At the thermal transition an abrupt drop in the mobility is observed, of which the magnitude decreases with increasing branching. The branching points appear to act as scattering points for both exciton and charge carrier migration.

Photobleaching Comparison of Poly(methylphenylsilylene) and Poly(phenylsilyne)

“…All of these processes lead to a disruption of the bonding along the Si chain and thus destroy the absorption associated with the → * transition. However, vibrational spectra 21 and electric conductivity measurements 22 of the polysilynes are best explained by less delocalization. This is seen clearly in Fig.…”

Synthesis and Characterization of Fluorescent Polymer−Metal Nanocomposites Comprising Poly(silylene-co-silyne)s and Silver Nanoparticles

“…For 5, PL emission bands associated with linear (361 nm) and branched polysilyne units show a perceptible variation in their intensities as compared to that of 1 suggesting higher order of branching and are in accord with those of analogous branched polysilanes reported earlier. 38,39 Strong evidence in favor of the network structure of 6 comes from 29 Si{ 1 H} NMR chemical shift [δ 8.36 (Et 3 Si), À56 to À70 (br, backbone)] as well as PL emission bands at 407, 430, 460 nm. The polymers 1, 2 and 6 have been chosen as representatives for cyclic voltammetric studies with Hg/Hg 2 Cl 2 as the reference electrode.…”

“…22,23 Synthetic methods of these composites primarily rely on the use of external reducing agents and organic based functional dendrimers/multi arm star copolymers and biomolecules as templates which have the desirable properties to stabilize or encapsulate metal nanoclusters. 24À30 Despite these developments, potential applications of higher dimensional silicon catenates such as polysilynes, 31À37 [RSi] n as well as poly(silylene-co-silyne)s, 38,39 [(R 2 Si) x -co-(RSi) 1-x ] n (also known as network and branched polysilanes respectively) in the synthetic domain of noble metal nanoparticles/clusters have not been explored so far. A detailed understanding of this aspect is desired in view of available information on the electronic properties of these polymers which differ appreciably from those of linear polysilanes.…”

“…35 Relevant studies on the optical properties of branched polysilanes by UVÀvis and PL (emission) spectroscopy as well as fluorescence lifetime decay measurements have shown that linear and branched units of these polymers more or less behave as separate chromophores and exhibit distinct photophysical properties. 38,39 On the basis of these studies, it is suggested that the extent of σ-delocalization in the skeletal backbone increases with higher degree of branching sites in the structural framework.…”

Optoelectronic Properties and Nanostructure Formation of σ-Conjugated Polymers

“…[25][26][27][28][29][30][31] The technique has been developed as an electrodeless method of monitoring the conductivity of a material which has been free from the effects due to the electrode interfaces. [32][33][34][35][36][37][38][39] Recently, the technique was successfully extended to the measurement of conductivity for isolated chains of conjugated polymers in dilute solution, yielding the intrinsic intra-chain conductivity along these chains in the absence of impurities, disordered structures in solids, or inter-molecular hopping processes. 26,27,37 Both -conjugated and -conjugated polymers exhibit remarkably high conductivities compared to the values of the corresponding bulk polymers determined by DC techniques, particularly for polymers bearing stiff backbones.…”