Controlling the Structure and Morphology of Organic Nanofilaments Using External Stimuli

Barış Sezgin; Jiao Liu; Diana P N Gonçalves; Chenhui Zhu; Tahir Tilki; Marianne E Prévôt; Torsten Hegmann

doi:10.1021/acsnanoscienceau.3c00005

Controlling the Structure and Morphology of Organic Nanofilaments Using External Stimuli

ACS Nanosci Au. 2023 Apr 18;3(4):295-309. doi: 10.1021/acsnanoscienceau.3c00005. eCollection 2023 Aug 16.

Authors

Barış Sezgin^{1

2}, Jiao Liu^{2

3}, Diana P N Gonçalves^{2

4}, Chenhui Zhu⁵, Tahir Tilki¹, Marianne E Prévôt², Torsten Hegmann^{2

3

4

6}

Affiliations

¹ Department of Chemistry, Süleyman Demirel University, 32260 Isparta, Çünür, Turkey.
² Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242 United States.
³ Materials Science Graduate Program, Kent State University, Kent, Ohio 44242 United States.
⁴ Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242 United States.
⁵ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 United States.
⁶ Brain Health Research Institute, Kent State University, Kent, Ohio 44242 United States.

Abstract

In our continuing pursuit to generate, understand, and control the morphology of organic nanofilaments formed by molecules with a bent molecular shape, we here report on two bent-core molecules specifically designed to permit a phase or morphology change upon exposure to an applied electric field or irradiation with UV light. To trigger a response to an applied electric field, conformationally rigid chiral (S,S)-2,3-difluorooctyloxy side chains were introduced, and to cause a response to UV light, an azobenzene core was incorporated into one of the arms of the rigid bent core. The phase behavior as well as structure and morphology of the formed phases and nanofilaments were analyzed using differential scanning calorimetry, cross-polarized optical microscopy, circular dichroism spectropolarimetry, scanning and transmission electron microscopy, UV-vis spectrophotometry, as well as X-ray diffraction experiments. Both bent-core molecules were characterized by the coexistence of two nanoscale morphologies, specifically helical nanofilaments (HNFs) and layered nanocylinders, prior to exposure to an external stimulus and independent of the cooling rate from the isotropic liquid. The application of an electric field triggers the disappearance of crystalline nanofilaments and instead leads to the formation of a tilted smectic liquid crystal phase for the material featuring chiral difluorinated side chains, whereas irradiation with UV light results in the disappearance of the nanocylinders and the sole formation of HNFs for the azobenzene-containing material. Combined results of this experimental study reveal that in addition to controlling the rate of cooling, applied electric fields and UV irradiation can be used to expand the toolkit for structural and morphological control of suitably designed bent-core molecule-based structures at the nanoscale.