Liquid-Crystalline Behavior and Structure of Charge-Transfer Complexes of Pyrene Derivatives with Four Linear Alkanoyloxy Substituents

Abstract

Pyrene derivatives (PCns) bearing four linear alkanoyloxy chains (n = 7, 9, 11, 15) were synthesized and shown to exhibit mesophases as a result of forming charge-transfer (CT) complexes with strongly electron-accepting 2,4,5,7-tetranitro-9-fluorenone (TeNF). The mesomorphic properties were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and variable-temperature X-ray diffraction (XRD) studies. The discotic lamellar phase was confirmed by XRD measurements, but no indication of intercalation of TeNF was observed. The CT complexation was supported by not only spectroscopic studies but the thermal behavior of the co-ground mixture.

Keywords:

• Charge-transfer complex
• lamellar structure
• tetraalkanoyloxypyrenes
• 2,4,5,7-tetranitro-9-fluorenone

Acknowledgments

The authors thank Professor Kazuchika Ohta of Shinshu University for his useful discussion and suggestions.

Notes

^a Heating and cooling scan rates were 5°C min⁻¹.

^b Abbreviations. Cr: Crystalline, I: Isotropic.

^a Cooling scan rate: 5°C min⁻¹.

^b Abbreviations; Cr: Crystalline, I: Isotropic, D_L: Discotic lamellar.

^c Phase separation of TeNF was observed.

^a l: Molecular length.

^b Determined by single-crystal structure.

^c Estimated by MM2.

Heating scan rate was 5°C min⁻¹.

Abbreviations: Cr: Crystalline, D_L: Discotic lamellar,.

I: Isotropic, X: Undetermined.

^a Gradually grows between 112°C and 124°C.

^b Gradually melts between 124–165°C.

^c Melts at 256°C but no transition is detected in the DSC measurement trace.

Crystallographic data of PC7 and PC9 have been deposited with the Cambridge Crystallographic Data Center: Deposition numbers CCDC-XXXXX and CCDC-YYYYY, respectively.

Symmetry transformations used to generate equivalent atoms: #1 −x + 1, −y, −z.