공융 결정법을 이용한 높은 결정성을 가지는 유기 전하 이동 복합체의 제조 및 특성 연구

Abstract

Charge transfer complexes (CT) have been widely studied for several decades. Due to their unique chemical and physical properties, CT complexes have been of great interested in the various fields of science and technology. Especially, organic CT complexes exhibiting semiconducting properties are investigated for novel optoelectronic materials. Since the optical and electronic properties of CT complexes are highly dependent on the molecular arrangement, profound study is further demanded for optimizing the performance of optoelectronic devices based on CT complexes. To this end, control of the crystal structure and crystallinity is crucial. Analysis of donor-acceptor (D-A) overlap, stacking structure, and degree of charge transfer between the donor and acceptor molecules could yield much insight into the structure-function relationship of these materials and a rational design of CT with electrical properties ranging from insulating to metallic. In this dissertation research focused on fabrications and characterizations of organic CT complexes via eutectic system. In the first part, hetero-microtubular organic CT complexes created by eutectic melting method will be presented. The microtubes consisting of 1,2,4,5-tetracyanobenzene (TCNB) and naphthalene (NAP) CT complex are fabricated by eutectic crystallization. The eutectic crystallization is carried out by melting TCNB and NAP at eutectic temperature (Te), and subsequently co-crystallize by lowering the temperature below Te. Comparing with other conventional solution growth methods, our eutectic crystallization method is fast and controllable. In this case, the microtubules form small cracks, and which are used to create heterogeneously doped microtubular CT complexes. The structure of the resulting heteromicrotubules are characterized by fluorescence microscopy, scanning electron microscopy (SEM), fluorescence spectrometer and fluorescence confocal microscopy. The second part of this dissertation will focus on fabrication of the heterogeneous CT nanorods by strain-induced melt-molding lithography. The strain-induced melt-molding lithography utilizes the formation of cracks by lateral strain and the selective doping of the secondary CT complex at the crack sites. TCNB-NAP is used to form CT complex nanorods and various aromatic compounds including pyrene (PY), 9-methylanthracene (9MA), and phenanthrene (PNT) are used for doping materials. Utilizing the lowered melting temperature by the formation of eutectic mixture, the well-defined CT complex nanorods can be easily fabricated by soft-lithography-assisted melt crystallization below 100 C. The morphology of heterogeneous CT nanorods is characterized by fluorescence optical microscopy and scanning electron microscopy (SEM). The uniaxial strain is applied to the polydimethylsiloxane (PDMS) mold by using universal testing machine (UTM). The hetero-nanorods were fabricated by selective doping of the secondary CT complex at defects induced by applying the uniaxial strain. Finally, I will discuss about conductivity and crystallinity of organic CT complexes prepared by eutectic melting method. For this purpose, tetrathiafulvalene (TTF) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) are used to make CT complexes. For the preparation of TTF-F4TCNQ CT complex thin films, ternary mixtures of TTF, F4TCNQ and naphthalene are used for the eutectic crystallization. Eutectic-melting-assisted nanoimprinting (EMAN) is used to fabricate well-defined nanopatterns of CT complexes. The CT complex nanorods are characterized by using fluorescence optical microscopy, scanning electron microscopy (SEM). The element of CT complex micro-patterns is characterized by using an energy dispersive X-ray spectroscopy (EDX). Electrical characterizations of the film devices are measured on a four-point probe in ambient condition at room temperature. Four point probe measurements demonstrate that the TTF-F4TCNQ CT complex is potential candidate for field effect transistors. Furthermore, the theoretical quantum chemical calculations have all been conducted using Materials Studio v. 7.0 and VASP software. Calculated and measured electronic property show qualitatively comparable results. In summary, it is well demonstrated that our eutectic crystallization is versatile for crystallizing various organic CT complexes. Furthermore, it is confirmed that the crystal structure and crystallinity of organic CT complexes can be controlled by the eutectic crystallization.