1
Introduction

1.1 Research Status of Photofunctional Polymer Composites

1.1.1 Photofunctional Materials

Photofunctional materials refer to the optical materials that use the principle that the optical properties of the material itself (such as refractive index or induced electric polarization) change under the action of the external field (such as electricity, light, magnetic, thermal, acoustic, and force) to achieve the detection, modulation, and energy or frequency conversion of the incident light signal. With the rapid advancements in modern science and technology, photofunctional materials are driving profound changes in many high-tech fields. Their application not only broadens the channel of energy acquisition but also exerts far-reaching influence on information storage, display technology, medical diagnosis and treatment, and other fields [1-3].

At present, the world is facing problems such as energy crisis and environmental pollution, which seriously affect the sustainable development of society. Traditional materials have gradually revealed their limitations in dealing with these complex problems. First of all, the traditional materials used for energy conversion and storage are less efficient, and it is difficult to make full use of renewable energy, resulting in significant reliance on fossil fuels, exacerbating the energy crisis. Secondly, the problem of environmental pollution is becoming increasingly prominent, and the production and use of traditional materials are often accompanied by high energy consumption and a large number of pollutants, which is not in line with the eco-friendly development model. In addition, with the increasing aging of the global population, the demand for medical health has increased significantly, but traditional materials have shortcomings in biocompatibility, intelligent responsiveness, and versatility, and it is difficult to meet the requirements of precision medicine and personalized health management [4]. For example, traditional materials used for medical device implantation are less biocompatible and may trigger inflammatory responses. In the field of disease diagnosis and treatment, traditional materials have a single function, making it difficult to achieve multifunctional synergies and dynamic response effects. In addition, the development of modern information and intelligence requires materials with higher performance, while the shortcomings of traditional materials in terms of flexibility, lightweight, and intelligent response limit the further breakthrough of emerging technologies [5]. At the same time, with the acceleration of digitalization, traditional materials are also showing limitations in the face of high-speed data transmission, large-capacity storage, and digital medical needs. Therefore, new, efficient, and sustainable materials are urgently needed for social development.

As an important material, photofunctional materials stand out in many fields by virtue of their excellent photoelectric conversion efficiency, photosensitive response characteristics, and photocatalytic ability, and become one of the key materials to promote the sustainable development of society. In the field of green energy, solar cells based on light-functional materials are widely used, effectively reducing the dependence on fossil energy, promoting the use of renewable energy, thus easing the energy crisis. At the same time, the photocatalytic degradation technology of photofunctional materials has shown great potential in reducing air pollution and water pollution, significantly reducing the emission of industrial harmful substances, and promoting environmental protection and green development. In the field of information storage and communication technology, photofunctional materials play a central role because of their excellent optical properties and low-loss characteristics. Optical fiber communication uses photofunctional materials to transmit data, which not only greatly improves the transmission rate but also effectively avoids electromagnetic interference, and realizes high-speed, remote, and large-capacity real-time data transmission. In the area of display technology, materials used in organic light-emitting diode (OLED) have been gradually applied to mainstream display technology with their excellent self-luminous characteristics, high contrast, and low energy consumption advantages, and have achieved the popularity of ultrathin and flexible displays [6]. In addition, photofunctional materials have also made significant progress in biomedical fields such as disease diagnosis, precision treatment, and health monitoring. For example, photodynamic therapy (PDT) relies on photosensitizers to produce reactive oxygen species (ROS) upon illumination with light at specific wavelengths, thereby selectively killing cancer cells, which is a noninvasive treatment with low side effects [7]. With its high-resolution imaging capability, fluorescence imaging technology has achieved remarkable results in the accurate diagnosis of tumors and other diseases, greatly improving the efficiency and accuracy of diagnosis and treatment. With their excellent physical and chemical properties, photofunctional materials are gradually replacing traditional materials and have widespread use in areas like energy, environmental protection, information technology, and biomedicine. They are becoming an important force to cope with global challenges and promote sustainable development.

According to the composition and structural characteristics, photofunctional materials can be divided into inorganic materials and organic materials (Figure 1.1). Both have their own characteristics in molecular structure, optical properties, and application fields, and occupy an important position in modern science and technology. Inorganic photofunctional materials usually have a highly ordered crystal structure, showing excellent stability, electrical conductivity, and optical properties, while organic photofunctional materials have unique advantages in some fields of application because of their good processability, flexibility, and adjustability.

Figure 1.1 Inorganic and organic photofunctional materials.

Inorganic photofunctional materials are mainly composed of metals, semiconductors, or their compounds (such as oxides, nitrides, or halides). Their structure gives them excellent stability, electrical conductivity, and optical properties, making them play an important role in high-precision optoelectronic applications. For example, oxide materials (such as TiO2 and ZnO) are widely used in the fields of photocatalysis, photodetectors, and sensors due to their excellent chemical stability and photocatalytic properties. Nitride materials, such as GaN and InN, play a key role in efficient light-emitting and high-power electronic devices, as the core material of modern LED technology. Perovskites are outstanding in the field of solar cells and photodetectors for their high photoelectric conversion efficiency and excellent machinability. In addition, gold nanoclusters (AuNCs), as a class of metallic nanomaterials with unique optical properties, have received considerable interest within the area of photofunctional materials lately. Due to their small particle size and quantum effect, AuNCs exhibit unique fluorescence characteristics and are widely used in biological imaging, sensors, and catalytic reactions.

Organic photofunctional materials are usually composed of carbon-containing molecules or polymers with conjugated p-electron systems in their molecular structures. This structure gives organic materials unique optical properties and good processing flexibility, making them show great potential in flexible electronics, wearable devices, display technology, and other emerging fields. For example, conjugated polymers (CPs) achieve efficient photoelectric conversion and luminous properties through the intramolecular p-electron delocalization effect. In addition, fluorescent dyes such as rhodamine and indole compounds are widely used in biological imaging, sensors, and laser labeling due to their excellent luminous efficiency and tunability. With the continuous development of organic materials, new organic semiconductors and fluorescent materials continue to emerge, further promoting the application of organic optoelectronic devices in the fields of intelligent display, wearable sensors, and optical communication technology.

Although inorganic and organic photofunctional materials show certain advantages in their respective application fields, there are also many shortcomings. These defects hinder their application in some fields. Inorganic materials are often brittle and difficult to adapt to flexible substrates, affecting their universality in flexible electronics, smart displays, and wearable technologies. In addition, the preparation of many inorganic materials is complex and costly, limiting the feasibility of large-scale, low-cost manufacturing. For example, although oxide and nitride materials perform well in photocatalytic and photoelectric conversion performance, the preparation process requires operating under high temperature and pressure, which makes manufacturing costly. Although the photoelectric conversion efficiency of perovskite is excellent, its stability is poor, and it is susceptible to deterioration under the influence of moisture, air, and ultraviolet light, and lacks long-term reliability. In contrast, organic materials have the advantages of...