**Chapter 7 163**

Tetradentate Platinum(II) Emitters: Design Strategies, Photophysics, and OLED Applications *by Huiyang Li, Tsz-Lung Lam, Liangliang Yan, Lei Dai, Byoungki Choi, Yong-Suk Cho, Yoonhyun Kwak and Chi-Ming Che*

Preface

As output devices, displays are usually used to convey originated information from a machine to a person. The ability of display to provide valuable and reliable information in real time is very important for better tracking of information and facilitating rapid decision-making. Displays are generally used in different devices such as televisions, laptops, monitors, mobiles, and smartphones. From 1922 to now, the display industry has experienced rapid growth and expansion with no signs of slowing down. For example, plasma displays, field emission displays, and electronic papers are examples of the continued expansion of display technology. In addition, organic light-emitting diodes (LEDs) and Digital Light Processing (DLP) technology are other contenders for leadership in display technology. Many believe that the microLED is the next generation of display technology, and leading players in LED, display, original equipment material (OEM), and others are pursuing it. Differentiated from liquid crystal display (LCD) and organic light-emitting diode (OLED), microLED is considered to be the only display technology that has no size limitation. Nevertheless, new trends such as LCD displays have increased demand for displays due to their light weight, low operating power, and compact design. LCD displays are applied in almost all displays smaller than 65" and therefore they dominate the current display market. However, they sufer from their intrinsic limitation to go larger in size. Any small-screened electronics such as digital watches, cell phones, and laptops can be produced by LCDs. The liquid crystals are a different state of matter and exhibit different molecular arrangements from the liquid and solid states. Liquid crystals promise to fill a vast array of uses in the future. Due to the progressive physical, chemical, electrical, and optical properties of liquid crystals, they exhibit various electronic and optical functions that make them candidates for a variety of engineering applications such as displays, sensors, energy-related technologies, electro-photonics, and so on. They can be used to produce faster-responding displays and serve as building blocks of next-generation optoelectronic devices. For instance, QD-LCDs are employed in TVs, and an increasing number of consumers prefer to buy this kind of TV. Other kinds of displays have different advantages and disadvantages. High-resolution images can be produced by field emission displays without a bulky appearance. Excellent quality images can be generated by plasma displays on very large screens. LED displays are already used in huge public displays. To compete with them, microLEDs should identify their unique value propositions or value proposition combinations to offer advantages. In addition, it seems that OLEDs are taking an increasing market share mainly in smart phone displays. In our modern world, touchscreen displays are used in a wide variety of devices and are standard on handheld gadgets like smartphones and tablets. Accordingly, high-quality displays can drive technology evolution in which new approaches and innovative ideas in information presentation will be realized.

This book, *Liquid Crystals and Display Technology*, provides an overview of the recent advances in the synthesis of liquid crystals and displays manufacturing and their emerging applications for output devices. This book has two sections. In the first, the chapters focus on nematic liquid crystals. The first chapter discusses fundamental (and already well-known) issues regarding uniaxial and biaxial nematic phases. The next three chapters examine alignment and controlling of nematic
