Original article: Yanling Zhuang et al., "Organic photoresponsive materials for information storage"

The fast-growing amount of data that are produced every year creates an urgent need for ultracapacity storage media. Light has many unique advantages including easy accessibility, no need of physical contact, high spatial and temporal resolution, and easy tuning of emission wavelength and intensity, showing great convenience in information storage in a noninvasive manner. Therefore, optical storage has become a significant data storage technology in the information age and has been widely applied in daily life, economy and military due to its large capacity, long lifetime, and low energy consumption. Photoresponsive materials can well realize information recording and readout because they can undergo a series of reversible changes in certain physical and chemical properties in response to light stimulus, which are specifically manifested as variations in optical properties (absorption and emission properties), conformation, electrochemical properties, conductivity, refractive index, etc. Among these variations, optical properties play a decisive role in information storage because the success of information (re)writing and erasing, encryption and decryption, and anti-counterfeiting is directly judged by the change in the color and/or luminescent color of photoresponsive materials. Organic photoresponsive materials are one of the most promising candidates for information storage owing to their light weight, low cost, high flexibility, good scalability, and compatibility with large-area solution-processing techniques including inkjet printing and screen printing. More importantly, their storage characteristics can be easily regulated through molecular design-cum-synthesis strategies. In light of the rapid development in this area, it is very necessary to systematically sum up and discuss the current research progress, and point out the future development of the entire research field of organic photoresponsive materials for information storage.

@Representative organic photochromic molecular parents for information storage and their photoisomerization processes: (a) diarylethene, (b) spiropyran, and (c) azobenzene.

Researchers from Nanjing University of Posts and Telecommunications recently summarized the recent research progress concerning organic photoresponsive materials for information storage. The authors first systematically summarized the design strategies and photoswitching mechanisms for various kinds of organic photoresponsive materials, including small organic molecules, metal complexes, polymers, supramolecules, and cholesteric liquid crystals. These materials exhibit reversible changes of absorption and/or emission properties in response to different wavelengths of light. Their photoswitching characteristics usually depend on light-triggered isomerization of photochromic and/or photofluorochromic units like ring opening-closure reaction and/or trans-cis isomerization, which result in the variations at the molecular and macroscopic scale. Subsequently, the authors introduced in detail the application of these organic materials in information storage, such as data (re)writing and erasing, encryption and decryption, and anti-counterfeiting. Finally, the authors discussed the current challenges and future directions in this rapidly growing research field. They proposed that novel organic photoresponsive information storage materials can be developed by proposing new molecular design-cum-synthesis strategies and photoswitching mechanisms, and advanced and multi-level information storage will be realized by optimizing device structures, improving device fabrication techniques and modifying the doped polymer and substrate structures.

This work provides a comprehensive summary of the application of organic photoresponsive materials in information storage, and also provides important guidance on the future works about the design of excellent organic photoresponsive materials for optoelectronic applications.