Kazuma TAKAHARA

Stimuli‐responsive photoluminescent materials exhibiting vapochromic behavior have attracted considerable interest because of their potential applications in chemical sensing and adaptive optical devices. Although copper(I) iodide clusters are well known for their vapochromic luminescence arising from the structural flexibility of Cu─I frameworks, hydrogen‐bonded Cu(I) architectures with dynamic host–guest interactions remain rare. Herein, we report a series of hydrogen‐bonded Cu─I network architectures assembled from identical molecular building blocks, exhibiting multicolor crystalline photoluminescence and structure‐dependent responses to solvent vapor. Depending on the Cu─I assembly mode, three distinct architectures, namely a polymorphic one‐dimensional single‐ladder chain, a double‐ladder chain, and a cubane‐like molecular cluster, were obtained and structurally characterized. The single‐ladder framework exhibits polymorphism accompanied by distinct emission colors. N , N ‐dimethylformamide (DMF) desorption induced on/off switching in emission intensity for the double‐ladder chain and a change in emission color in the cubane‐like molecular cluster. Both photoluminescence responses were reversible upon re‐exposure to DMF vapor; however, recovery of the initial long‐range crystal structure occurred only in the double‐ladder chain. The Cu─I assembly mode thus gives rise to two distinct PL‐reversible vapochromism: intensity switching and color switching. These findings establish hydrogen‐bond‐assisted structural design for tuning how guest exchange modulates photoluminescence intensity and color.

Abstract A new photoluminescent platinum(II) complex, cis-[PtCl2(ppt)], where ppt = 2-(2-pyridyl)-4-phenylthiazole, has been synthesized and characterized. Two polymorphs of the complex were isolated with high phase purity: an orange crystalline phase O-Cryst and a yellow crystalline phase Y-Cryst, each exhibiting distinct solid-state photoluminescence. Partially amorphous phases derived from the respective polymorphs, O-Ground and Y-Ground, were prepared by mechanical grinding. Upon exposure to acetone vapor, both amorphous phases recrystallized exclusively to the O-Cryst. The structural difference among the crystalline and amorphous phases was investigated by powder X-ray diffraction and pair distribution function (PDF) analysis, with the latter clearly revealing the local molecular packing that is inaccessible by conventional diffraction techniques. Density functional theory calculations correlated the relative energies and molecular geometry in the respective solids with the observed photoluminescence color variations. The difference in the dihedral angles between the pyridyl and phenyl rings of the ppt ligand was found to strongly govern the availability of π-delocalized orbitals, thereby accounting for the polymorphism-dependent color variation. The stimuli-induced crystal−amorphous−crystal transformation described here provides a straightforward design principle for fine-tuning of the solid-state photoluminescence while emphasizing the enormous utility of PDF analysis for elucidating local structures and the mechanisms of phase transformation in molecular crystals.

Crystallisation behaviors of M–Tb–M complexes were varied depending on the solvents, exhibiting absolute spontaneous resolution or formation of meso-type isomers.