A Record Chromophore Density in High‐Entropy Liquids of Two Low‐Melting Perylenes: A New Strategy for Liquid Chromophores

Abstract Liquid chromophores constitute a rare but intriguing class of molecules that are in high demand for the design of luminescent inks, liquid semiconductors, and solar energy storage materials. The most common way to achieve liquid chromophores involves the introduction of long alkyl chains, which, however, significantly reduces the chromophore density. Here, strategy is presented that allows for the preparation of liquid chromophores with a minimal increase in molecular weight, using the important class of perylenes as an example. Two synergistic effects are harnessed: (1) the judicious positioning of short alkyl substituents, and (2) equimolar mixing, which in unison results in a liquid material. A series of 1‐alkyl perylene derivatives is synthesized and it is found that short ethyl or butyl chains reduce the melting temperature from 278 °C to as little as 70 °C. Then, two low‐melting derivatives are mixed, which results in materials that do not crystallize due to the increased configurational entropy of the system. As a result, liquid chromophores with the lowest reported molecular weight increase compared to the neat chromophore are obtained. The mixing strategy is readily applicable to other π‐conjugated systems and, hence, promises to yield a wide range of low molecular weight liquid chromophores.


2,5,8,11-tetra-tert-Butylperylene (2i)
Large amounts of 2i was synthesized using a literature procedure 2 according to which a 20 mL microwave vial was charged with Perylene (1a) (3.9 mmol, 1.0 g), ferric chloride (5.15 mmol, 835 mg) under nitrogen. Chlorobenzene (7 mL) was added to the above mixture followed by addition of t-BuBr (43.9 mmol, 4.93 mL) and reaction was allowed to stir at 95 °C for 5h. 2 Afterwards, DCM was added (50 mL) and contents were passed through a short column of basic alumina. Organic layer was extracted with H2O thrice, solvent was removed under vacuum.
Column chromatography using basic alumina and cyclohexane as an eluent resulted in pure

2-tert-Butylperylene (2j)
We tried to optimize conditions to get 2j as the major product. In most of the cases crude 1 H NMR indicated large amount of starting material perylene and minor peaks for 2-tertbutylperylene (2j) with small amounts of 2,5-di-tert-butylperylene (2j'). However reaction under dilute conditions and with excess of tert-butylchloride resulted in much better yields for 2j. 2,3

Reaction of 2a' with Oxygen
1-Butyl-1,12b-dihydroperylene (2a') (25 mg) was dissolved in hexane (5 mL) and connected to O2 balloon. After 12 h, 1 H NMR was checked which showed signals corresponding to 2a' decreased and an increase in signals for 2a is observed. Figure S25. Overlay of spectrum before and after reaction with oxygen in CDCl3.

Single crystal X-ray of 2c
Method and data: X-Ray crystallographic data was obtained on Single Crystal X-ray diffractometer Bruker D8 VENTURE which is equipped with the PHOTON 100CMOS detector. The diffractometer is equipped with Incotec Cu Kα (λ = 1.54184 Å) or Mo Kα (λ = 0.71073 Å) microfocus X-ray sources, and a Cryojet low-temperature device. The cryojet was used to lower the temperature to 100K for data collection. A small crystal of about 0,1 * 0.05 * 0.03 mm in size was used for collecting the single crystal data. The crystal was gently mounted on a string loop and studied at cryo conditions. A full sphere of data to 0.65 Å resolution was collected with the Mo radiation source. In total about 20h of data collection, no change or physical deformation was observed in the mounted crystal.
The data were processed using APEX3 software. Unit cell dimensions were refined using the entire data sets. The structure was solved (direct methods) and refined (full-matrix least-squares on F2) using SHELXL. Non-hydrogen atoms were refined anisotropically, while hydrogen atoms were introduced at calculated positions as riding on their corresponding carbon atoms and refined isotropically. Geometric calculations were carried out using the Shelx, PLATON