Mixed Rubrene Cocrystals Offer Insights into Intermolecular Interactions Influencing Crystal Packing

Abstract

We report the first examples of mixed cocrystallization in rubrene derivatives. We grew crystals with differing ratios of two previously characterized rubrene derivatives. When crystallized individually, each rubrene derivative packs with a twisted tetracene core in the solid state. In both examples of mixed cocrystallization, the tetracene cores are planar, providing some of the first experimental evidence that intermolecular interactions are a major driving factor for planarization of the tetracene core. Additionally, a larger ratio of the methylated rubrene derivative resulted in a mixed cocrystal displaying a herringbone crystal formation, which is optimal for applications in optoelectronics.

Correlating structure and photophysical properties in thiazolo[5,4-d]thiazole crystal derivatives for use in solid-state photonic and fluorescence-based optical devices

“…This region represents lattice-phonon vibration frequencies and has been probed in various studies to identify intermolecular packing dependent effects on photophysical properties in organic crystals. 49–52 The low-energy modes are highly sensitive to molecular packing, which explains the observed difference shown above. All the spectra have been normalized by maintaining the CN vibration of the thiazole ring at 1388 cm −1 constant.…”

Killer Phonon Caught: Femtosecond Stimulated Raman Spectroscopy Identifies Phonon-Induced Control of Photophysics in Rubrene Derivatives

“…The closely matched molecular structure of the derivatives ensures that any observed differences in excited-state properties are more likely to result from changes to electronic and vibrational states rather than changes in molecular or crystal structure. Additionally, all derivatives needed to form the herringbone crystalline structure are known to be favorable for SF in rubrene . We synthesized a series of halogenated rubrene derivatives with substitutions on either the 5/11 or 5/12 peripheral phenyl rings (Figure ), as both positional combinations have led to herringbone rubrene structures with some substituents. ,, F1 is a 5/12 substituted rubrene and is the only previously synthesized derivative in this study.…”

“…Halogenation of rubrene increases the rate and efficiency of singlet fission compared to parent rubrene . We synthesized four halogenated rubrene derivatives which all pack with the herringbone crystal structure ideal for singlet fission . We used low-frequency Raman spectroscopy to identify the key phonons characteristic of this idealized herringbone structure.…”

“…For rubrene, the phonon frequencies occur in the range of 30−150 cm −1 , 33−35 which correspond to 0.2−1 picosecond (ps) delay times between photoexcitation pulses, well within the accessible time resolution for FSRS. 36 We record the time-dependent evolution of vibrational features following both single and dual photoexcitation pulses, dictated by different phonon frequencies. Comparison of these results leaves us with a method to experimentally quantify the effects of individual phonons on excited-state dynamics.…”