Hollow organic capsules assemble into cellular semiconductors

Self-assembly of electroactive molecules is a promising route to new types of functional semiconductors. Here we report a capsule-shaped molecule that assembles itself into a cellular semiconducting material. The interior space of the capsule with a volume of ~415 Å3 is a nanoenvironment that can accommodate a guest. To self-assemble these capsules into electronic materials, we functionalize the thiophene rings with bromines, which encode self-assembly into two-dimensional layers held together through halogen bonding interactions. In the solid state and in films, these two-dimensional layers assemble into the three-dimensional crystalline structure. This hollow material is able to form the active layer in field effect transistor devices. We find that the current of these devices has strong response to the guest’s interaction within the hollow spaces in the film. These devices are remarkable in their ability to distinguish, through their electrical response, between small differences in the guest.


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Supplementary Figure 10. The PDF for the brominated trimer (1-Br12) from the far detector measurement is overlaid with a PDF simulated from the structure obtained from SCXRD. The simulated PDF was generated using the program PDFgui 16 , calculated without any refinement, using experimental resolution parameters refined from the nickel standard data, (Qdamp = 0.008 Å -1 and Qbroad = 0.015 Å -1 ) the same Qmax = 6.33 Å -1 , a global isotropic thermal displacement parameter, Uiso = 0.03 Å 2 , further damped by an envelope function with structural coherence of 400 Å, and rescaled for comparison. While there are differences, it is clear that the signals remain in phase over the whole range indicating that the long range molecular packing in the powdered sample is fairly well represented by that of the single crystal.

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Supplementary Figure 11. Coherence length for 1. The high Q-resolution, low Qmax measurement is shown in black (Qmax = 6.33 Å -1 ). The high-r signal is obscured by noise. We reduce noise by reducing further the Qmax. Although reducing Qmax also reduces the real space resolution, the highr region is dominated by low frequency terms and therefore is still reliable for identifying structural signals. We therefore reduced the Qmax to 1.76 Å -1 and visually locate where the signal becomes flat. We give an estimated lower bound on this value at 65 Å (blue dotted line) and upper bound of 120 Å (green dotted line).        Atomic force microscopy (AFM) was performed with a PSIA XE100.

1 H and 13 C NMR spectra
Powder X-ray diffraction data were collected on a PANalytical X'Pert 3 Powder Diffractometer. Data was collected on powder samples and films drop-cast from chloroform solution and p-xylene solution. For all data collection a Si zero-background holder was used.
Single crystal data for 1-Br12 was collected on an Agilent SuperNova diffractometer using a mirror-monochromated Cu Ka radiation. The hexagonal-shaped crystals were mounted on a MiTeGen Kapton loop (polyimide). These were cooled to 100 K with an Oxford Cryosystems nitrogen flow apparatus. Data integration, scaling (ABSPACK) and absorption correction were perfomed in CrysAlisPro. 2 Structure solution was performed using ShelXS, 3 ShelXT, 4 or SuperFlip. 5 Subsequent refinement was performed by full-matrix least-squares on F 2 in ShelXL.
Olex2 6 was used for viewing and to prepare CIF files. PLATON 7 was used for SQUEEZE, 8 ADDSYM 9 and TwinRotMat. Details of crystallographic data and refinement parameters are given in Table S2. Due to heavy disorder of the alkyl imide chains in 1-Br12, only nine carbons (out of eleven) in each alkyl fragment were modeled. The cavity size of 1-Br12 was calculated from the S30 solvent accessible volume calculator in Olex2. By employing this functionality we found discrete pockets within the structure of 1-Br12 which match the cavities of these molecules. Thus, the calculated cavity size of (SSS/RRR)-1-Br12 is 414.9 Å 3 (CalcSolv 3.0 Å probe, grid step 0.2 Å).
X-ray total scattering experiments (PDF analysis) were conducted on beamline 28-ID-2 at the National Synchrotron Light Source II at Brookhaven National Laboratory. An X-ray beam of energy 67.756 keV (l = 0.18299 Å) was focused on samples loaded into Kapton capillaries.
Scattered intensities were collected at room temperature, in rapid acquisition mode 10  to-detector distance gives a smaller Q-range of 0.20-6.33 Å -1 , which gives a lower real space resolution, but provides a much better Q-resolution of the scattering which allows the resulting PDFs to be analyzed over longer real-space distances 14,15 In this case, the Qmax was reduced further

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to decrease the noise level below any signal observable at high distances. The structural coherence of the sample was estimated from visual observation of the distance at which the structural signal became indistinguishable from the average atomic density, ( ) = 0.
It is important to note the following for the coherence length estimation: (1)