Segmented poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] via xanthate and dithiocarbamate precursors: A comparative study of thermal eliminations

Abstract

Segmented poly[2-methoxy-5-(2-ethylhexloxy)-1,4-phenylene vinylene] (MEH-PPV)-x's, which contain conjugated segments of varying lengths that are interspersed by nonconjugated units along the polymer backbone, were synthesized by selective thermal elimination of precursors containing controlled amounts (x) of a thermally labile group, namely, xanthate or dithiocarbamate (DTC). These precursors were in turn synthesized by competitive nucleophilic substitution of the Wessling polyelectrolyte with varying molar fractions of the respective nucleophiles-potassium ethyl xanthate or sodium diethyl dithiocarbamate. Methanol, used as the reaction medium, also served to introduce the second thermally less labile nucleophilic substituent. This approach for the preparation of segmented MEH-PPV-x is superior to the previous approach that used acetate as the thermally labile group, because it offers greater control over the composition despite a simpler synthetic procedure. Detailed studies of the thermal-elimination kinetics of the three precursors, namely, acetate, xanthate, and DTC, both in solution and in thin films, were carried by in situ monitoring of their ultraviolet-visible spectra. These studies revealed that the rates of elimination followed the order, DTC Ͼ xanthate Ͼ acetate. The activation energies for the elimination were, however, not widely different (ca. 30 kcal/mol), suggesting that the rates primarily reflected differences in the pre-exponential factor. After elimination, the segmented MEH-PPV-x samples exhibited the expected redshift in their absorption and fluorescence spectra with an increasing molar fraction (x) of eliminated segments, which was accompanied by a drastic reduction in the fluorescence quantum yields.

An Efficient Bulk‐Heterojunction Photovoltaic Cell Based on Energy Transfer in Graded‐Bandgap Polymers

“…15 %). [17] A similar trend was observed in solid-state polymer films. In the blend of the two polymers the PL of the LC phase was completely quenched and the PL of the HC phase was enhanced.…”

“…1a) have recently been synthesized by selective elimination of side groups of a suitable precursor containing two types of eliminable groups, namely, diethyl dithiocarbamate (DTC) and methoxy groups. [17] Selective elimination of DTC groups, leaving the methoxy groups unaffected, leads to the generation of truncated MEH-PV oligomeric units, of varying conjugation lengths, within each polymer chain. This approach provides a It is demonstrated that the energy transfer from low-conjugated (LC) poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) to high-conjugated (HC) MEHPPV, coupled with significant electron transfer from HC-MEHPPV to an acceptor species, offers a viable route for an efficient photodiode over a wide spectral range.…”

Poly(phenylenevinylenes)

“…Soluble PPVs can be obtained by heating the precursor polymer 24b in 1,2-dichlorobenzene at 175 • C. Photoluminescence of PPV films suggests that the PPV from this dithiocarbamate precursor route may have slightly more defects than that from the sulfinyl precursor 20. The dithiocarbamate precursor route is also useful for preparation of segmented PPV derivatives via controlled elimination [54]. …”

Synthesis of graft copolymers based on polyphenylene xylylene and fullerene grafted polystyrene

“…Figure 7 shows FTIR spectra of the graft copolymer before and after reacting it with the fullerene. The spectrum shows two new weak transmission bands at 528 cm −1 and 577 cm −1 , which represent the characteristic of the fullerene‐bonded polymers 18. In addition, UV–vis absorption spectra of the product from ATRA (Fig.…”