Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

We report on the impact on the equatorial and meridional orientation in hairy-rod poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] thin films when blended with tris-cyclometalated oligo-fluorenylpyridine iridium(III) complex. The presence of this transition-metal complex does not alter the underlying helical motif of the polymer chain or the hexagonal unit-cell intermolecular packing. However, systematic changes in the resulting texture patterning of the crystallites are observed. Crystallites with two preferred $a\text{−}b$ orientations, so called type I and II and differing by $30\text{degrees}$, are superimposed on an isotropic background that is designated as type III. The extent of meridional alignment for all three is found to be similar.

Figure 1

Above: Dichroic ratio (open symbols) and order parameter $s$ (solid symbols) of nematic 8/15-PF2/6 (squares) and hexagonal 29/68-PF2/6 (circles) with $\mathrm{Ir}{\left({\mathrm{Fl}}_x\mathrm{Py}\right)}_3$, ($x=1$, 3, or 5) complex. Below: Schematics of PF2/6, $\mathrm{Ir}{\left({\mathrm{Fl}}_x\mathrm{Py}\right)}_3$ $(x=1,3,5)$, and an experimental geometry. $\varphi$ is the angle between the incident beam and $\mathbf{z}$ axis in the $\left(0yz\right)$ plane.

Figure 2

Above: GIXD patterns of $5\mathrm{wt.}\%$ $\mathrm{Ir}{\left({\mathrm{Fl}}_5\mathrm{Py}\right)}_3$ doped 29/68-PF2/6. (a) $\left(xy0\right)$ plane. (b) $\left(x0z\right)$ plane. The GIXD patterns were measured with the incident beam along the $\mathbf{z}$ and $\mathbf{y}$ axes, respectively. Black and white indices show the primary reflections of the types I and II, respectively. Type III appears as diffraction arcs. Below: Schematics of the proposed arrangement of crystallite types I–III.

Figure 3

Integrated intensities of the first hexagonal GIX reflections of 29/68-PF2/6 mixed by $5\mathrm{wt.}\%$ $\mathrm{Ir}{\left({\mathrm{Fl}}_5\mathrm{Py}\right)}_3$. The sample is rotated about the $\mathbf{x}$ axis and $\varphi$ is the angle between incident beam and $\mathbf{z}$ axis. Open spheres: Reflections 010, 110, 100, and $0\overline{1}0$ of type I. Solid squares: $\overline{1}00$ and 110 of type II. Open diamonds: arcs representing type III. This curve is multiplied by 4 for clarity. Labels denote clockwise rotation around the $\mathbf{z}$ axis (cf. Fig. 2). Solid lines are corresponding Gaussian fits.

Figure 4

Typical AFM images of 29/68-PF2/6 mixed by $5\mathrm{wt.}\%$ $\mathrm{Ir}{\left({\mathrm{Fl}}_5\mathrm{Py}\right)}_3$. The height from black to white is (a) $30\mathrm{nm}$, (b) $20\mathrm{nm}$, (c) $15\mathrm{nm}$, and (d) $5\mathrm{nm}$. Inset shows the experimental geometry depicted in Figs. 1, 2. Examples of areas rich in regular voids are marked by white lines and arrows.