Pressure-Induced Restricting Intermolecular Vibration of a Herringbone Dimer for Significantly Enhanced Multicolor Emission in Rotor-Free Truxene Crystals

Abstract

Organic solid-state luminescent materials exhibit numerous exciting photoelectric properties that are central to emergent organic light-emitting diodes, smart sensors, and data encryption. However, the luminescence of pure organic rotor-free materials has been afflicted with strong intermolecular π−π stacking interactions. Herein, an unprecedented pressureinduced emission enhancement (PIEE) is realized in a system of rigid planar pure polycyclic aromatics, i.e., truxene crystals. The emission intensity is enhanced 7-fold below 3.0 GPa with a photoluminescence quantum yield increased to 10.17% compared with the initial value of 1.78%, and the emission colors change from green (520 nm) to red (640 nm) within 11.8 GPa. Spectral characterizations and first-principles calculations reveal that the PIEE and piezochromism can mainly be attributed to the restricted intermolecular vibration and the decreased energy gap. Our findings enrich the PIEE mechanism and provide a new guideline for designing pressureresponsive luminescent materials in advancing their photoelectric applications.

Maximized Green Photoluminescence in Tb‐Based Metal–Organic Framework via Pressure‐Treated Engineering

“…Then, the PL intensity started to decrease with pressure until the PL disappeared completely upon 16.5 GPa (Figure S6). This phenomenon indicated that the enhancement of the π–π interaction played a leading role in the weakening of PL intensity [18] . During the decompression process, a remarkable emission increasement appeared and pressure‐treated Tb(BTC)(H 2 O) 6 showed a monochromatic emission enhancement (Figure 2b,c).…”

“…This phenomenon indicated that the enhancement of the π-π interaction played a leading role in the weakening of PL intensity. [18] During the decompression process, a remarkable emission increasement appeared and pressure-treated Tb(BTC)(H 2 O) 6 showed a monochromatic emission enhancement (Figure 2b,c). It is suggested that the energy levels of S 1 and T 1 after pressure treatment were close to the metal ions, thereby enhancing the PL intensity by improving the efficiency of LMET.…”

Doping of charge-transfer molecules in cocrystals for the design of materials with novel piezo-activated luminescence

“…[13][14][15][16] In particular, organic molecular crystals with weak intermolecular interactions, such as van der Waals forces, hydrogen bonding, charge transfer, etc., have been attracting intensive research interest in this field, in which πconjugated molecules are commonly used as building blocks due to their unique optical and electronic properties combined with their high sensitivity to the environment. [17][18][19] According to the tight binding model, compression induced strengthening of intermolecular interactions could widen energy bands and thus reduce the energy gap, 20 while the enhanced interactions such as π-π interaction, could also lead to emission quenching. 21 Therefore, most luminescent materials known so far show a gradually red-shifted and quenched emission upon compression.…”

Conformational Flexibility-Controlled Piezochromic Behavior of Organic Fluorophores

“…In contrast, the pressure-induced emission enhancement (PIEE) phenomenon was discovered in many systems. − Zou et al found that tetraphenylethene shows PIEE with an extra pressure in the range of 1.5 to 5.3 GPa owing to the enhanced intermolecular C–H···π and C–H···C interactions . PIEE is also observed in a rotor-free truxene crystal because of the effective restriction of the intermolecular vibration of dimers packed in herringbone . The perylene-1,2,4,5-tetracyanobezene cocrystal exhibits blue-shifted and enhanced emission upon compression within 3 GPa due to the tailored donor–acceptor interactions by inserting tetrahydrofuran molecules .…”

“…22 PIEE is also observed in a rotor-free truxene crystal because of the effective restriction of the intermolecular vibration of dimers packed in herringbone. 23 The perylene-1,2,4,5-tetracyanobezene cocrystal exhibits blueshifted and enhanced emission upon compression within 3 GPa due to the tailored donor−acceptor interactions by inserting tetrahydrofuran molecules. 24 Thus, the pressureresponsive photophysical properties of organic luminescent materials are complex and highly system-dependent.…”