Colloidal perovskite nanocrystals based on formamidinium lead halide (FAPbX 3 ) have been synthesized by the ligand-assisted reprecipitation method using PbX 2 − dimethyl sulfoxide complexes as precursors at room temperature. Well-defined cubic-shaped FAPbX 3 nanocrystals have been obtained with a size d of ∼10 nm. The synthesized FAPbX 3 nanocrystals show bright photoluminescence with a high photoluminescence quantum yield (75% for FAPbBr 3 ). The lifetimes of FAPbBr 3 nanocrystals were measured for the samples isolated at several different centrifugal speeds. The photoluminescence can be tuned from the blue to nearinfrared region (λ peak = 408−784 nm) by changing either the amount of oleylamine or the composition of X. The color expression range is 135% of the NTSC standard. The bandwidth of the photoluminescence spectra of FAPbX 3 nanocrystals is narrow (full width at half-maximum of 18−48 nm). FAPbX 3 nanocrystals show thermal stability that is better than that of MAPbBr 3 nanocrystals.

Owing to their stimulus responsive color changing properties, polydiacetylenes (PDAs) have been extensively investigated as colorimetric sensors. Thermochromic properties of PDAs have been the central focus of a number of investigations that were aimed not only at gaining a fundamental understanding of the physical basis of the color change but also at developing practical applications as temperature sensors. The thermochromic transition temperature of a PDA polymer is closely related to the melting point of the corresponding diacetylene (DA) monomer. In addition, the majority of PDAs described to date undergo a blue-to-red color change above room temperature because PDAs are generally derived from DA monomers that have melting points above room temperature. In the current study, we developed a series of low temperature colorimetric PDAs that were designed based on the reasoning that removal of the sources for strong headgroup interactions would lower the melting points of the corresponding DA monomers. This strategy was used to design and fabrication of PDA sensors that display color transitions in the range of 5−30 °C. Moreover, the thermochromic transition temperatures of the PDAs were found to decrease by ca. 10 °C when the alkyl chain length in the DA monomer is truncated by two methylene units. The results of FTIR and Raman spectroscopic analyses suggest that the PDA alkyl chain adopts an all-trans conformation in the blue-phase and some gauche forms exist in the alkyl chain in the red-phase PDA. Finally, the new PDAs are stable up to 300 °C, and their processable nature enables them to be fabricated in nanofiber forms by employing an anodized aluminum oxide (AAO) membrane as a template.

Perovskite nanoparticle composite films with capability of high-resolution patterning (≥2 µm) and excellent resistance to various aqueous and organic solvents are prepared by in situ photosynthesis of acrylate polymers and formamidinium lead halide (FAPbX ) nanoparticles. Both positive- and negative-tone patterns of FAPbX nanoparticles are created by controlling the size exclusive flow of nanoparticles in polymer networks. The position of nanoparticles is spatially controlled in both lateral and vertical directions. The composite films show high photoluminescence quantum yield (up to 44%) and broad color tunability in visible region (λ = 465-630 nm).