[18a-P7-1~23] 12.4 Organic light-emitting devices and organic transistors

[18a-P7-23] Role of Alkyl-Chain Layers in Herringbone-Type Molecular Packing of Organic Semiconductor Single Molecular Bilayers

〇Shunto Arai^1,2, Kaede Morita¹, Jun'ya Tsutsumi², Mutsuo Tanaka², Tatsuo Hasegawa^1,2 (1.Univ. of Tokyo, 2.AIST)

Keywords:Organic semiconductors, Single molecular bilayers, Herringbone-type molecular packing

Controlling self-assembly of organic molecules is a key nanotechnology to realize solution-based device fabrication. Particularly, it was an enormous challenge to control the thickness of single crystalline thin films. We have recently established a methodology to form single molecular bilayers (SMBs) of organic semiconductors composed of an extended $\pi$-conjugated frameworks substituted by an alkyl chain ($\pi$Core-Cn). These SMBs are produced by blade-coating of a solution containing two $\pi$Core-Cns with different alkyl chain lengths. Though the method is useful for the production of SMB-based efficient thin film transistors (TFTs), the intralayer molecular packing and the role of alkyl chains for the production of SMBs remain elusive.
Here we report the physical factor which dominates the in-plane herring-bone type molecular packing of SMBs revealed by the systematic measurements of polarized optical absorption spectra of SMBs. The intralayer packing of SMBs is determined by the intermolecular interactions of shorter chain molecules and the longer alkyl chains act as a geometrical frustration for multilayer crystallisation. This finding gives a principle to arrange the device performance of SMB-based TFTs.