Self-assembly of multi-stranded perylene dye J-aggregates in columnar liquid-crystalline phases

Many discoid dyes self-assemble into columnar liquid-crystalline (LC) phases with packing arrangements that are undesired for photonic applications due to H-type exciton coupling. Here, we report a series of crystalline and LC perylene bisimides (PBIs) self-assembling into single or multi-stranded (two, three, and four strands) aggregates with predominant J-type exciton coupling. These differences in the supramolecular packing and optical properties are achieved by molecular design variations of tetra-bay phenoxy-dendronized PBIs with two N–H groups at the imide positions. The self-assembly is driven by hydrogen bonding, slipped π–π stacking, nanosegregation, and steric requirements of the peripheral building blocks. We could determine the impact of the packing motifs on the spectroscopic properties and demonstrate different J- and H-type coupling contributions between the chromophores. Our findings on structure–property relationships and strong J-couplings in bulk LC materials open a new avenue in the molecular engineering of PBI J-aggregates with prospective applications in photonics.


Density measurements by the buoyancy method at 20 °C
Density measurements were carried out in mixtures of deionized water and aqueous sodium chloride (20 wt%) solution. Prior to dissolving, sodium chloride (pro analysi) was dried at 150 °C under reduced pressure (1 × 10 -3 mbar). Both solvents were degassed by ultrasonication.
The samples were molten to the isotropic liquid in order to avoid inclusion of air. Subsequently, the samples were extruded into a thin solid fiber and cut into a number of small pieces of varying size (0.1 -0.6 mg). The samples were put in a sealed vial containing deionized water at 20 °C.
Aqueous sodium chloride (20 wt%) solution was added in small portions until the sample started floating. The mixture was allowed to equilibrate between additions. The necessary weight percentage of sodium chloride was determined and the density was calculated according to reference 5.
Note that this method relies on samples which are free from air inclusions, which cannot be guaranteed strictly with the present preparation of the samples. For materials with much lower clearing temperatures and high thermal stability in the isotropic liquid, the samples can be prepared by keeping them a long time in the isotropic liquid under vacuum, which is supposed to eliminate all air bubbles. S6 However, in the present case this is not possible since the PBIs decompose slowly at such high temperatures (>240 °C). Therefore, the present density value is a lower limit for PBI 2 and PBI 4.

Extrapolation of the molecular volumes at higher temperatures and the calculation of the numbers of molecules per columnar stratum (PBI 2, PBI 3 and PBI 4)
From the density measurements at 20 °C the molecular volumes can be obtained by Vmol =    Therefore, the first sharp reflection that can be seen directly at the meridian corresponds to the half pitch.
The helical pitch and repeat of the 81 helix was calculated to be 7.1 Å × 16 = 113.6 Å. The quite strong reflection at 3.55 Å is in agreement with the 0032 reflection caused by this helix.

Supplementary Note 3. Polarized UV-Vis measurements.
The change of the ratio of the first and second vibrational transition of the S0-S1 electronic transition of the aggregate was compared to the one of the monomer. Since the ratio increases in the solid state for aggregates, it shows that most of the oscillator strength is concentrated in the 0,0 transition, which is a typical signature for J-aggregates.
To describe the quality of the alignment the dichroic ratio Dλ and the order parameter Sλ were calculated for each PBI.

Supplementary Note 4. FT-IR and polarized FT-IR experiments.
The PBI 1 sample was pressed between two KBr plates and heated up to 160 °C to form a thin film, which was investigated by temperature-dependent FT-IR measurements on a cooling process in transmission mode by using a heating stage. During decreasing temperature from 160 °C (isotropic liquid) to 150 °C (crystalline state) a new NH vibration band appeared at 3170 cm −1 while the NH vibration band at 3390 cm −1 completely disappeared (Supplementary Figure 12). According to literature, the NH vibration at 3390 cm −1 was assigned to free NH. [11][12][13] Considering the weakening of the NH bond strength upon Hbonding the raising of the NH vibration band at lower wavenumbers was assigned to the hydrogen-bonded NH between the imide groups in the crystalline state.    Calculation of the correlation lengths of π-stacks.
The correlation lengths ξ in the bulk state were calculated according to the Scherrer equation 14 : Where K is the dimensionless shape factor with a typical value of 0.9, λ the X-ray wavelength, ∆(2θ) the line broadening at fwhm in radians and θ the Bragg angle in °.
∆(2θ) and θ were determined by fitting the peak on the equator belonging to the - stacking distance.
The number of correlated molecules N was calculated referring to N = ξ / - distance.
The calculated number of molecules, which are in strong correlation, supports the analysis of the selfassembled structures of double-(4), triple-(3 and 2 at higher temperatures) and quadruple-stranded (2 at lower temperatures). The fiber diffraction patterns of PBI 2 (Colr), 3 and 4 were simulated with CLEARER using the modelled structure, which were obtained via Materials Studio. The data were exported as PDB-files and loaded into the Fiber Diffraction Simulation module of CLEARER. 15 To fit the pattern the fiber axis was set to (0,0,1) with a "crystallite size" of 130 nm (a), 130 nm (b) and 60 nm (c). The "crystal size" has been adapted to best fit the pattern. The cell dimensions were set to experimental parameters. The fiber disorder parameters σθ and σϕ were 0.08 radians and infinite with a sample interval of 1 pixel. The contrast was adjusted to best visualize the signals of the pattern. It has to be considered that in this program the liquid crystal fiber is simulated as a perfectly ordered domain of a given size on the basis of one unit cell with the given orientational disorder of the domains. In comparison, a real liquid crystal is not built with identical unit cells. In addition, the model cannot be simulated simultaneously with conveniently ordered aromatic building blocks and liquid-like chains, since the geometry optimization optimizes always both building blocks. For the most complex rectangular unit cell the geometry optimization affords a unit cell deviating from the body-centred structure and therefore also reflections may reveal, which are extinct in  −173 −597 a Exciton coupling energies J were calculated within the point-dipole approximation following Kasha's theory. The sign (+/−) specifies the type of contribution and is negative exciton coupling energy (J-type coupling) and positive exciton coupling energy (H-type coupling). α is always 0°.