High Contrast and Bright Emission Piezochromic Fluorescence in Organic Crystals via Pressure Modulated Exciton Coupling Effect

Abstract

With its recent debut in various fields, piezochromic fluorescent (PCF) materials have attracted considerable attention due to their unique photophysical features with dynamically reversible emission wavelength and intensity. Herein, a novel luminogen DBCT is developed, which is sensitive to external pressure and displays dual color reversibly switched PCF fluorescence. The solid state emission can switch from bright orange (O) (λem = 586 nm, Φsolid = 0.47) to deep red (R) emission (λem = 646 nm, Φsolid = 0.34) with high contrast through pressing (0.6 MPa), heating and fuming processes. Single crystal X‐ray analysis and theoretical calculations verify that the reversible luminescence switching characteristic is highly related to the different molecular packing mode within O and R crystals, which amplifies the exciton coupling (EC) effect and results in good PCF performances with high Φsolid as well as distinguishable red‐shifted emission. With such multiple advantages that writable fluorescent inks are successfully fabricated with high contrast for security anti‐counterfeiting applications based on DBCT molecules. This research may offer an important guideline for molecular design of PCF materials and enrich the underlying mechanism of mechanochromic luminescence, which also broadens the real‐life applications of smart materials.

Organic Crystalline Optical Waveguides That Remain Elastic from −196 to ≈200 °C

“…This compound is soluble in common organic solvents and displays weak yellow emission in solution (Figure 1b). Yellow thin prismatic crystals (Figure 1c) with length of ≈0.5-2.0 cm and width of ≈0.5-2.0 mm (aspect ratios in the range of [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] were prepared by diffusion of ethanol into dichloromethane (DCM) solution (0.1 m) over about two weeks at ambient conditions. The basic optical properties of both solutions and crystalline samples were first characterized.…”

“…to be one of the core materials in future flexible organic optoelectronics. [1][2][3][4][5][6][7][8] However, the application of organic functional crystals in advanced optoelectronic devices is severely restricted by two major drawbacks-high brittleness and difficulties with implementation in devices. Generally, cracking or even fractures occur when external stress is applied onto organic crystals, and this proneness to damage increases the difficulties with fabricating allorganic crystal-based devices.…”

Low‐Pressure Sensitive Piezochromic Fluorescence Switching of Tetraphenylethylene‐Anthraquinone

“…[16] However, most of the piezochromic luminescent materials reported so far requires ultra-high pressure (~GPa level) for the efficient luminescence switching. [17] It is still very challenging and highly appealing to develop highly sensitive piezochromic molecules working at medium-and low-pressure regimes (~kPa level). [18] Herein, we design and synthesis low-pressure sensitive piezochromic molecules with twisted donor-acceptor (D-A) skeletons, tetraphenylethylene-anthraquinone (TPE-AQ), where a propeller-like tetraphenylethene (TPE) unit is employed as donor and a rigid anthraquinone (AQ) unit is acting as acceptor.…”

Precise peripheral design enables propeller-like squaraine dye with highly sensitive and wide-range piezochromism

“…1a). This precise peripheral design is expected to enhance its ICT effect further and cause multiple "so interactions" (such as C-H/p and C-H/N/O interactions) to loosen the molecular packing pattern, [40][41][42] which both are crucial to the sensitivity and switching range under mechanical stimuli. Eventually, we demonstrated the highly sensitive and wide-range piezochromic switching of SQ-NMe 2 microcrystals under mechanical grinding (Fig.…”