MA02.02.04 : Confinement Effects on Structural Features of π-Conjugated Molecules

3:30 PM–4:00 PM Apr 3, 2018

PCC West, 100 Level, Room 102 BC

Natalie Stingelin1

1, Georgia Institute of Technology, Atlanta, Georgia, United States

Typical devices manufactured from π-conjugated molecular materials, such as field-effect transistors and organic solar cells, are based on architectures where the material is processed to have characteristic features from the nano- to the micrometer scale. Some finite size effects during solidification may thereby occur; however, little attention has been paid so far to these and how they may affect relevant structural features of π-conjugated systems<!--[endif]---->. We will present initial data on the structure development of a model conjugated system – i.e. 7,7′-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl)bis(6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole), p-DTS(FBTTh2)2 – using as confinement medium anodic aluminum oxide (AAO) templates consisting of hexagonal arrays of cylindrical nanopores with diameters ranging from 25 to 400 nm. Confinement leads to a notably different phase behavior compared to the bulk. We find, for example, a pronounced depression of the crystallization temperature of p-DTS(FBTTh2)2, indicating a change of nucleation mechanism from heterogeneous nucleation for bulk materials to a (likely) homogeneous mechanism in confinement. Moreover, we show that the temperatures of the phase transitions are dependent on the degree of confinement. Most strikingly, a confinement-induced new thermotropic mesophase is demonstrated that is absent in the bulk material. Since the p-DTS(FBTTh2)2 can also be textured through use of confinement effects, a new set of tools, thus, is made available to create well-defined microstructures to establish and probe important structure/property interrelationships of this class of materials.<!--![endif]---->