在光電元件中，有機金屬錯合物佔據大部分的市場，但也造成價格不菲主因。反觀近幾年，有機材料的部分，純的有機系統之熱活化行延遲螢光 性質與設計及在光電應用也蓬勃發展起來。為了深入解有機分子材料的光物理特性，可以透過理論計算的方式來研究，使其在未來應用上有重大突破。
本論文將探討有機分子系統之光物理性質，特別針對有機分子中透過異碳原子(如：硫、氧)所產生Tm到Sn之間逆向系統間跨越（Reverse Intersystem crossing,RISC）而形成TADF機制之影響參數進行研究。高原子序之異碳原子的重原子效應產生之強自旋-軌道交互作用力 （spin -orbit coupling, SOC），可以增強逆向系統間跨越的效率，使其有利於讓三重態激子回到單重態放出螢光。若能有效的提升逆向系統間跨越的效率，就可間接提高有機系統放光的量子產率，因此RISC速率的 大小是很多光電材料應用上關鍵因素。本篇將對各種不同類別的包含異 碳原子之分子系統進行討論，以理論計算方法預測這些異碳原子對系統的SOC與ΔEST的影響，並與分子的結構影響做比較。最終希望能找出影響 有機系統關鍵因素且創造出一個具有小的ΔEST與較高的SOC。我們主要以 氧(Oxygen)、硫(Sulfur)及硼(Boron)等含異碳原子系統為討論對象，探討我們將著重在電荷轉移激發態(CT)、nπ*和ππ*激發態的定量與定性分析上 。
本篇將針對以下幾點進行討論，包含電子結構、鍵長、電子躍遷性質、單重態與三重態能階差等，也對高TADF放光效率的有機分子系統進行一系列的探討。

In the field of light emitting diodes, organometallic complexes have the largest contribution, but these systems are usually toxic and suffer from high production costs. On the other hand, in recent years, pure organic materials receive a lot of attention due to the “thermally activated delayedfluorescence” (TADF) phenomenon. To better understand the photophysical properties of organic molecular materials, in this thesis, we perform theoretical calculations to study the properties of emissive organic systems and propose molecular design principles for future photovoltaic applications.
In this thesis, we investigate the photophysical properties of organic molecular systems, especially for organic molecules containing heteroatoms. The rate of reverse intersystem crossing (RISC) from a triplet state (Tm) to a singlet state (Sn), which governs the mechanism of TADF, is studied. We explore the heavy atom effect originated from heavy heteroatoms that cause strong spin-orbit coupling (SOC) effect in the hope that it will enhance the efficiency of RISC pathway. A variety of different types of molecular systems containing heteroatoms are discussed via theoretical calculations. The effect of these heteroatoms are evaluated via the SOC integral and ΔE, the energy gap between low-lying singlet and triplet excited states. The influence ofthe molecular structure is also examined. Ultimately, we intend to find the key factors that ensure a small ΔE and a large SOC, which lead to strong TADF in pure organic systems. Oxygen, sulfur and boron are the major heteroatoms discussed in this thesis.Qualitative and quantitative analysesof the charge transfer (CT), ππ*, andππ* states are performed. In particular, we would focus on properties such as the electronic structure, bond lengths, nature of the electronic transitions, singlet and triplet state energy levels, and etc.

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