Nanoscale Organization and Solid-State Dynamics of Carbazole-[π]-Carbazole Rotors Edged with Aliphatic Chains

Abstract

The aggregation behavior and its influence on the intramolecular motion of three highly conjugated solidstate molecular rotors 2−4 with alkyl groups were investigated by a combination of fluorescence spectroscopy, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and variable-temperature solid-state 2 H nuclear magnetic resonance (VT 2 H ssNMR). Their long conjugation made them highly emissive in tetrahydrofuran solution (Φ f = 0.41, 0.21, and 0.18, for rotors 2, 3 and 4, respectively), and the elongated aromatic cores favored π−π intermolecular interactions upon aggregation in hexane. The TEM micrographs and PXRD studies of the resulting bulk showed that shorter chains generated larger amorphous domains in 2, as compared to 3 and 4. The 2 H ssNMR experiments showed fast intramolecular rotation of their central 1,4-diethynylphenylenes with the lowest activation energy to rotation for compound 2, E a = 5.34 kcal/mol. This relationship between amorphous/ crystalline domains and intramolecular motion has not been reported before, and it could guide the design of new solid-state molecular rotors.

Synthesis of Rigid Rod, Trigonal, and Tetrahedral Nucleobase-Terminated Molecules

“…The MALDI-TOF analysis was performed on an Autoflex III (Bruker, USA). 12 In a 250 mL three-necked round-bottomed flask was added 1,4diiodobenzene (1; 5.0 g, 15.19 mmol), PdCl 2 (PPh 3 ) 2 (1.06 g, 1.51 mmol), CuI (144 mg, 0.75 mmol), ethynyltrimethylsilane (2; 4.92 mL, 34.94 mmol), anhyd THF (60 mL), and Et 3 N (10 mL, 72.91 mmol) under N 2 atmosphere. Then the reaction mixture was stirred for 2 h at RT, and then filtered through a pad of Celite.…”

“…1 H NMR (300 MHz, CDCl 3 ):  = 7.38 (s, 4 H), 0.24 (s, 18 H). 12 In a 250 mL round-bottomed flask, a mixture of 1,4-bis[(trimethylsilyl)ethynyl]benzene (4.18 g, 15.48 mmol), K 2 CO 3 (8.54 g, 61.92 mmol), and MeOH (80 mL) was stirred for 4 h at RT. The mixture was concentrated and redissolved in CH 2 Cl 2 (150 mL).…”

“…1,4-Diethynylbenzene ( 3 ) was prepared through a di-Sonogashira coupling with ethynyltrimethyl­silane ( 2 ) followed by base-promoted desilylation. 12 Another unit (4-iodophenyl)boronic acid ( 4 ) was generated via a selective monolithiation and subsequent boronation. 13 Both building blocks were prepared in gram-scales and in good yields (71% and 69%, respectively), which facilitated the following construction of each monomer.…”

How Do Molecular Motions Affect Structures and Properties at Molecule and Aggregate Levels?

“…On the other hand, the direct observation of molecular motions is not easy because of untouchable change of motion in isolated molecule. 6 Although molecular motions can be characterized using nuclear magnetic resonance, electron microscopes, spectroscopies, etc., [7][8][9][10][11] these technologies cannot perfectly present aggregate-state molecular motions in real time and in-situ manner. Therefore, MSP study at all levels of structural hierarchy is still attractive but challenging.…”

Visualization and Manipulation of Molecular Motion in the Solid State through Photoinduced Clusteroluminescence

“…In general, from gas to liquid to solid state, molecular motion becomes harder and harder because of the increased intra/intermolecular rigidification. Investigation of solid-state molecular motion is not only of scientific importance but also practically useful for developing solid-state molecular motors. , Several groups such as Aprahamian, Michl, Sozanni, Loeb, Naumov, Garcia-Garibay, and Irie have studied solid-state molecular motion in a single state or frame by nuclear magnetic resonance (NMR), electron microscopes, spectroscopies, etc. − However, these technologies are difficult, if not impossible, to realize in situ, on-site, and real-time visualization of solid-state molecular motion simultaneously. , Besides visualization, manipulation of the molecular motion is also important. Many stimuli such as light, pH, temperature, electricity, etc.…”