Crystal packing control of a trifluoromethyl‐substituted furan/phenylene co‐oligomer
01 Oct 2018-Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry (International Union of Crystallography (IUCr))-Vol. 74, Iss: 5, pp 450-457
TL;DR: Terminal trifluoromethyl groups induce weak intermolecular interactions which control the crystal packing and optical properties of co-oligomer single crystals, which exhibit high photoluminescence efficiency and have optical properties which strongly depend on the crystalpacking.
Abstract: Furan/phenylene co-oligomer single crystals are considered as future materials for organic optoelectronics. Here, the effects of trifluoromethyl substituents on the crystallization, structure and optical properties of furan/phenylene co-oligomer 1,4-bis{5-[4-(trifluoromethyl)phenyl]furan-2-yl}benzene are studied systematically. The solution growth methods and physical vapor transport result in the formation of three polymorphs depending on the growth method and the solvent. Single-crystal X-ray analysis reveals the crystal structures to correspond to H-, J- or mixed aggregates. All obtained crystals exhibit high photoluminescence efficiency and have optical properties which strongly depend on the crystal packing. Variable-temperature X-ray powder diffraction analysis shows the thermal transition of two forms (H- and J-aggregates) into a third one (mixed aggregate). Terminal trifluoromethyl groups induce weak intermolecular interactions which control the crystal packing and optical properties of co-oligomer single crystals.
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TL;DR: The unraveled relationships between the structure and the properties of the substituted PTTPs should facilitate a rational design of π-conjugated (co-)oligomers for efficient organic optoelectronic devices.
Abstract: Owing to the combination of efficient charge transport and bright luminescence, thiophene–phenylene co-oligomers (TPCOs) are promising materials for organic light-emitting devices such as diodes, transistors and lasers. The synthetic flexibility of TPCOs enables facile tuning of their properties. In this study, we address the effect of various electron-donating and electron-withdrawing symmetric terminal substituents (fluorine, methyl, trifluoromethyl, methoxy, tert-butyl, and trimethylsilyl) on frontier orbitals, charge distribution, static polarizabilities, molecular vibrations, bandgaps and photoluminescence quantum yields of 5,5′-diphenyl-2,2′-bithiophene (PTTP). By combining DFT calculations with cyclic voltammetry and absorption, photoluminescence, and Raman spectroscopies, we show that symmetric terminal substitution tunes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies of TPCOs within a range of ∼0.7 eV, shifts the frequencies of the vibrational modes associated with the phenyl rings, changes the photoluminescence quantum yield by about two-fold and slightly changes the bandgap by ∼0.1 eV. We demonstrate that these effects are governed by two factors: the Hammet constant of the substituents and their involvement in the π-conjugation/hyperconjugation described by the effective conjugation length of the substituted oligomer. A detailed picture underlying the effect of the terminal substituents on the electronic, vibrational and optical properties of TPCOs is presented. Overall, the unraveled relationships between the structure and the properties of the substituted PTTPs should facilitate a rational design of π-conjugated (co-)oligomers for efficient organic optoelectronic devices.
25 citations
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TL;DR: This work has shown that L-Leucinium hydrogen maleate crystals are very plastic at ambient conditions and at least down to 77 K, the first reported example of an organic compound remaining so plastic at cryogenic conditions.
Abstract: l-Leucinium hydrogen maleate crystals are very plastic at ambient conditions. Here it is shown that this plasticity is preserved at least down to 77 K. The structural changes in the temperature range 293–100 K were followed in order to rationalize the large anisotropic plasticity in this compound. To the best of our knowledge, this is the first reported example of an organic compound remaining so plastic at cryogenic conditions.
17 citations
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TL;DR: The synthesis, growth from solutions and structure of crystals of a new linear thiophene-phenylene co-oligomer with a central benzothiadiazole fragment with a conjugated core, (TMS-2T-Ph)2-BTD, are presented.
Abstract: The synthesis, growth from solutions and structure of crystals of a new linear thiophene–phenylene co-oligomer with a central benzothiadiazole fragment with a conjugated core, (TMS-2T-Ph)2-BTD, are presented. Single-crystal samples in the form of needles with a length of up to 7 mm were grown and their crystal structure was determined at 85 K and 293 K using single-crystal X-ray diffraction. The conformational differences between the crystal structures are insignificant. The parameters of melting and liquid crystalline phase transitions of (TMS-2T-Ph)2-BTD were established using differential scanning calorimetry and the thermal stability of the crystals was investigated using thermogravimetric analysis. The optical absorption and photoluminescence spectra of the solutions and crystals of (TMS-2T-Ph)2-BTD were obtained, and the kinetics of their photodegradation under the action of UV radiation were studied.
6 citations
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TL;DR: In this paper, the authors introduced alkyl substituents in AIE-active bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)thiophene and elucidated their effect on the molecular and crystal structures, crystallization and optical properties of materials.
Abstract: Aggregation-induced emission (AIE) materials find their applications in organic optoelectronics, bio-imaging and sensors. In this work, we introduced alkyl substituents in AIE-active bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)thiophene and elucidated their effect on the molecular and crystal structures, crystallization and optical properties of materials. Ethyl-containing (C2-BFMPT) and octyl-containing (C8-BFMPT) 2,5-bis(4-((2,7-dialkyl-9H-fluoren-9-ylidene)methyl)phenyl)thiophenes were synthesized in 4 steps. The introduction of alkyl groups weakened intermolecular interactions, decreased the crystal quality, melting point, and density, and increased the solubility of materials. Octyl-containing derivative was demonstrated to generate two crystal forms obtained by the native (form I) and additive-assisted (form II) crystallizations. The latter appeared to have a better crystal quality. C–H⋯π interactions and an extensive positional disorder were revealed for both derivatives. In C8-BFMPT crystals (form II) only a half of molecular backbones were well localized due to multiple intermolecular C–H⋯π interactions, whereas another half demonstrated a high positional disorder. The AIE effect with a negligible photoluminescence (PL) quantum yield (QY) in solution and a PL QY of 5% for C2-BFMPT and 2% for C8-BFMPT (form II) crystals was demonstrated. The cooling of the C8-BFMPT form II resulted in 10-fold increase of PL QY. The introduction of alkyl-substituents and additive-assisted crystallization are highlighted as powerful tools for the control of crystal packing, morphology, polymorphism and the optical performance of AIE-materials.
2 citations
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TL;DR: An overview of the current possibilities of ORCA is provided and its efficiency is documents.
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TL;DR: The use of standards for the measurement of photoluminescence quantum yields (QYs) in dilute solutions is reviewed in this paper, where only three standards can be considered well-founded.
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1,592 citations