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

Weili Zeng,Hong Chen,Yujie Song,Jianning Zhang,Wangqiao Chen,Ming Liu

doi:10.3390/ma14185269

Abstract

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.

Highlights

Near-infrared (NIR) radiation (700–2500 nm) accounts for 52% of the solar energy from sunlight, and significantly contributes to the energy accumulation and temperature elevation of various man-made concrete buildings, which results in the urban heat island (UHI) effect, and greatly increases the electricity energy consumption [1,2,3,4]
For the compounds with same alkyl groups, the NIR reflectance will increase as the degree or length of the conjugated backbone increases, especially for the reflectance from 1750 nm to 2500 nm
Despite the different functional groups, NIR reflectance will vary within a certain interval for a compound with special backbone; (2) the alkyl or amine group will generally deteriorate the NIR reflectance

Summary

Introduction

Near-infrared (NIR) radiation (700–2500 nm) accounts for 52% of the solar energy from sunlight, and significantly contributes to the energy accumulation and temperature elevation of various man-made concrete buildings, which results in the urban heat island (UHI) effect, and greatly increases the electricity energy consumption (i.e., cooling) [1,2,3,4]. NIR reflective pigments can be classified into two groups: inorganic compounds [5,6,7,8] (i.e., titanium oxide, chromium oxide, and rare-earth oxide, etc.,) and organic compounds [9,10,11,12] (i.e., perylenetetracarboxylic diimide (PDI), azo-compounds, and copper phthalocyanine). Compared to certain inorganic counterparts, organic pigments are becoming the research focus due to their low toxicity, biocompatibility, and cost effectiveness [13,14,15,16,17,18,19]. For certain organic compounds with suitable molecular structure, such as thiophene-fused-heteroaromatic diones, they exhibited relatively good stability and almost had no decomposition after exposing to air for three months [20]

Methods

Results

Conclusion