Stereocontrolled Synthesis and Optical Properties of All-cis Poly(phenylene vinylenes) (PPVs):  A Method for Direct Patterning of PPVs

Abstract

Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-type polycondensation of 2,5-dioctyloxy-1,4-benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes, which are prepared by ruthenium-catalyzed (Z)-selective double hydrosilylation of diethynylbenzenes, followed by bromodesilylation of the resulting (Z,Z)-bis(2-silylethenyl)benzenes with N-bromosuccinimide. The all-cis PPVs thus obtained undergo one-way photoisomerization to the corresponding trans-PPVs both in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a quartz substrate.

Thermal, Structural, and Viscoelastic Characterization of cis-Poly(phenylene vinylene) Related to its Photo-Isomerization

“…This sample mimicked the solvent-cast film utilized in the photo-isomerization experiment. 1 The G 0 and G 00 data at 26 C measured for this as-cast/dried sample agreed well with those of the quenched sample (unfilled squares in Figure 3), suggesting that the PPV chains had the same relaxation rate/thermal mobility in the cast and quenched samples.…”

“…This sample mimicked the solventcast film utilized in the photo-isomerization experiments. 1 The quenched and cast samples exhibited similar viscoelastic relaxation behavior that reflected the large-scale thermal motion of the amorphous cis-PPV chains. Figures 1 and 2, respectively, show the DSC and WAXD profiles of the cis-PPV sample.…”

“…The apparent number-average molecular weight and the polydispersity index, both determined from GPC calibration with polystyrene standards, were M n ¼ 4300 and M w =M n ¼ 2:16, respectively. 1 The as-poly- merized sample was obtained in a powder form, and the heat-treated and/or solvent cast sample was a sticky bulk material at room temperature.…”

“…1,2 The PPV, having the structure shown in Scheme 1, is a -conjugated polymer offering applications to light-emitting diodes, 3 solar cells, 4 and so on. In these applications, it is very useful if we can make arbitrary patterning of thin PPV films cast on appropriate substrates.…”

“…This photo-isomerization, followed by rinsing with solvents, provides us with an interesting route of pattern-writing in the residual trans-PPV film by use of appropriate UV masks, as already demonstrated previously. 1 Because the photo-isomerization occurs rather quickly, the cis-PPV chains in the solvent-cast film are expected to be essentially in the amorphous state thereby exhibiting fast changes of their large-scale conformation. (It is quite unlikely that the isomerization occurs quickly for the chains in a rigid crystalline state.)…”