Near-Infrared Absorption and Polarized Luminescent Ultrathin Films Based on Sulfonated Cyanines and Layered Double Hydroxide

Organic inorganic hybrid ultrathin films (UTFs) were fabricated by alternate assembly of sulfonated carbocyanine derivate (Scy) and exfoliated Mg-Al-layered double hydroxide (LDH) monolayers via layer-by-layer (LbL) method, which show uniform near-infrared (NIR) absorption and photoluminescence properties. UV-vis absorption and fluorescence spectroscopy indicate a stepwise and regular growth of the UTFs upon increasing deposition cycles. X-ray diffraction demonstrates that the UTFs possess periodical layered structure with the basal spacing of 3.3 nm; scanning electron microscopy and atomic force microscopy show that the UTFs surface are microscopically smooth and uniform. The Scy/LDH UTFs exhibit well-defined polarized photoemission character with the maximum luminescence anisotropy as high as Moreover, the Scy/LDH UTFs display higher stability than the pristine Scy, suggesting that the existence of LDH nanosheets enhance the thermal performance of the Scy dye. A molecular dynamics study was carried out to investigate the basal spacing and arrangement of Scy in the UTFs, and the results show that the Scy anions preferred to arrange within the LDH monolayer, which favor the improvement of the NIR polarized luminescence anisotropy of the Scy anions. Therefore, this work not only gives a facile method for fabricating NIR absorption and luminescence ultrathin film system but also provides a detailed understanding of the geometric structure of NIR photofunctional anions confined between the LDH monolayers.