苝四甲酸二酐一维纳米结构中激子跃迁行为调控的研究

Photophysical properties of organic semiconductor materials have close relationship with excitons transition, therefore, the modulation on excitions transition should be of great significance for the properties enhancement of organic light-emitting devices. At present, researchers can achieve excitons transition modulation in organic film by means of high pressure and annealing process which respectively affect molecular distance and crystallinity of organic film. However, pressure and annealing process barely influence the size and specified surface area of organic film, i.e., it is difficult to effectively modulate the amount ratio between the external excitons and the internal excitons of organic film. Furthermore, size effect and surface effect become more obvious with the dimension decrease of materials. Based on the above considerations, in this project, we will prepare organic semiconductor one-dimensional nanostructures, and control the length and specified surface area of these structures in order to modulate the amount ratio and transition energy of excitons. And we are going to study the Förster energy transfer between inorganic substrate and the organic nanostructure formed, to resolve the disagreement about whether or not energy transfer can help improving the emission intensity of organic materials. The main purposes are to improve the emission efficiency of organic nanomaterials and explore the critical mechanism of excitions transition. This could be served as the experiment guidance for the fabrication and performance enhancement of the miniature organic light-emitting devices.

有机半导体材料的光物理性质与材料中激子的跃迁行为紧密相关，因此调控激子的跃迁行为对提升有机发光器件的性能具有重要意义。目前，研究人员可以利用压力与退火来改变薄膜内有机分子间的距离以及薄膜的晶化程度，从而调控了薄膜中激子的跃迁能量。但是，压力与退火对薄膜的尺寸与比表面积的影响并不显著，难以有效地调控薄膜表面与薄膜内部的激子数目比；并且，材料性能的尺寸效应以及表面效应随着材料尺寸的降低变得越发显著。为此，本项目以有机半导体一维纳米结构为研究对象，通过调节一维纳米结构的长度以及比表面积，从而实现“表面激子”与“内部激子”数目比及激子跃迁能量的调控。并研究无机衬底与有机纳米结构之间的Förster能量转移，解决人们在能量转移能否提高有机材料发光强度认识上的分歧。本项目的最终目的是提高有机纳米材料的发光效率、了解调控激子跃迁行为的关键机制。这将为小型有机发光器件的制备、性能优化提供实验依据。

有机半导体的光物理性能与激子跃迁关系密切，对激子跃迁的调控将有助于提高有机半导体的光物理性能。此前，人们已经能够通过退火、加压的方式来改变晶态有机半导体材料的结晶程度及分子间距，以此来实现对有机晶体中激子跃迁的调控。上述激子跃迁的调控手段比较繁琐，而简化有机半导体中激子跃迁的调控手段仍然存在着挑战，这正式本项目的研究重点。在本项目的执行期间，项目负责人与合作者成功地在阳极氧化铝(AAO)衬底表面制备了苝四甲酸二酐、酞菁铁、酞菁铜等多种有机发光材料的纳米结构，利用AAO自身的结构特点调控了生成的纳米结构的形貌，并通过生长过程的衬底温度调节了分子取向程度；在此基础上，着重研究了PTCDA纳米结构的光物理特性，调控了PTCDA纳米结构中的激子跃迁，探索了调控激子跃迁的机制。扫描电镜给出的形貌结果与光致发光的测量结果表明，随着生成结构比表面积的提高，结构中占支配地位的激子类型由Frenkel激子转变为单分子激子，通过调控两种激子的比例可以实现发光谱中主发射峰能量的转换。荧光衰减的研究结果表明，对于连续的薄膜，内部分子排列的规整性为影响荧光寿命的主要因素。随着结构比表面积的提高，表面分子的取向对荧光寿命的影响越发显著。在本项目的资助下取得的研究成果已经发表在Journal of Materials Science，Journal of Superconductivity and Novel Magnetism，The Journal of Physical Chemistry Letters，以及Applied Physics Letters杂志上。这些研究结果将为有机半导体光物理特性的调控、及有机发光器件性能的提升提供实验依据。