Designing structural order in electronically active organic solids remains agreat challenge in the field of materials chemistry.Now,2Dpoly(arylene vinylene)s prepared as highly crystalline covalent organic frameworks (COFs) by basecatalyzeda ldol condensation of trimethyltriazine with aromatic dialdehydes are reported. The synthesized polymers are highly emissive (quantum yield of up to 50 %), as commonly observed in their 1D analogues poly(phenylene vinylene)s.The inherent well-defined porosity (surface area ca. 1000 m 2 g À1 , pore diameter ca. 11 for the terephthaldehyde derived COF-1) and 2D structure of these COFs also present an ew set of properties and are likely responsible for the emission color, which is sensitive to the environment. COF-1 is highly hydrophilic and reveals ad ramatic macroscopic structural reorganization that has not been previously observed in framework materials.

We report the first transformation between crystalline vinylene-linked two-dimensional (2D) polymers and crystalline cyclobutane-linked three-dimensional (3D) polymers. Specifically, absorption-edge irradiation of the 2D poly(arylenevinylene) covalent organic frameworks (COFs) results in topological [2+2] cycloaddition cross-linking the π-stacked layers in 3D COFs. The reaction is reversible and heating to 200C leads to a cycloreversion while retaining the COF crystallinity. The resulting difference in connectivity is manifested in the change of mechanical and electronic properties, including exfoliation, blue-shifted UV-Vis absorption, altered luminescence, modified band structure and different acid-doping behavior. The Li-impregnated 2D and 3D COFs show a significant ion conductivity of 1.8×10 −4 S/cm and 3.5×10 −5 S/cm, respectively. Even higher room temperature proton conductivity of 1.7×10 -2 S/cm and 2.2×10 -3 S/cm was found for H2SO4-treated 2D and 3D COFs, respectively.

Tetraphenylethene (TPE) substituted phenanthroimidazoles 3a and 3b were designed and synthesized by the Suzuki cross-coupling reaction. They show reversible mechanochromic behavior with contrast colors between sky-blue and yellow green. The powder XRD studies show that destruction of a crystalline state into an amorphous state is responsible for mechanochromism. Hydrogen bonding interaction of a cyano-group in 3b results in enhanced AIE and improved thermal stability.

Red luminescence is found in off-white tris(iodoperchlorophenyl)methane (3I-PTM H) crystals which is characterized by a high photoluminescence quantum yield (PLQY 91 %) and color purity (CIE coordinates 0.66, 0.34). The emission originates from the doublet excited state of the neutral radical 3I-PTM R , which is spontaneously formed and becomes embedded in the 3I-PTM H matrix. The radical defect can also be deliberately introduced into 3I-PTM H crystals which maintain a high PLQY with up to 4 % radical concentration. The immobilized iodinated radical demonstrates excellent photostability (estimated half-life > 1 year under continuous irradiation) and intriguing luminescent lifetime (69 ns). TD-DFT calculations demonstrate that electron-donating iodine atoms accelerate the radiative transition while the rigid halogen-bonded matrix suppresses the nonradiative decay.

In order to understand how the donor (D)/acceptor (A) substituents and their substitution pattern affect the solution and solid-state optical properties, a series of symmetrical and unsymmetrical TPE substituted BTDs 3−8 were designed and synthesized by the Suzuki and Stille coupling reactions. Their solvatochromic, aggregation induced emission (AIE), mechanochromic, and vapochromic properties were studied and compared. The single-crystal X-ray structures of BTDs 5 and 6 are reported. The BTDs 3− 8 are highly fluorescent with the tunable emissions. The solvent dependent emission was observed in BTDs 3−8 and their Lippert−Mataga plots show a linear correlation of the Stokes shift with solvent polarity. The emission study in different tetrahydrofuran (THF):water percentages show enhanced emission in aggregates. The BTDs exhibit a reversible multi-stimuli response toward mechanical force, solvent, and heat. The detailed study using single-crystal X-ray, photophysical properties, powder X-ray diffraction, scanning electron microscopy, and theoretical calculation reveals that the planarization induced enhancement in conjugation and conversion of crystalline to amorphous state are responsible for mechanochromism and vapochromism. Our work has elucidated that this general approach can be utilized to develop a promising class of multi-stimuli responsive materials.