Insights into the Intrinsic Factors Affecting the NIR Reflectance Based on Rylene Diimide Molecules

A clear understanding of the relationships between molecular structure and NIR reflectance (700–2500 nm) behavior is important and highly desirable for developing appropriate NIR-reflective materials to combat NIR heat radiation from sunlight. In this research, three groups of imide-based compounds have been adopted to investigate the influence of the intrinsic molecular structures on the NIR-reflective properties. It is found out that for the compounds with alkyl groups, the NIR reflectance will increase as the degree of the conjugated backbone increases, especially for the reflectance from 1750 nm to 2500 nm. In addition, despite that the alkyl or amine groups deteriorate the NIR reflectance, the NIR reflectance varies within a certain interval and the isomers with branched alkyl groups show identical or smaller NIR reflectance than those of isomers with linear alkyl groups. For different compounds, crystallinity seems to almost have no relationship with their NIR reflectance.