Camera Method for Monitoring a Mechanochromic Luminescent β-Diketone Dye with Rapid Recovery

Abstract

Mechanochromic luminescent (ML) materials, which show a change in emission due to an applied mechanical stimulus, are useful components in a variety of applications, including organic light-emitting diodes, force sensors, optical memory storage, and next-generation lighting materials. While there are many different ML active derivatives, few show room temperature self-erasing. Thin films of the methoxy substituted β-diketone, gbmOMe, initially exhibited blue (428 nm) emission; however, green (478 nm) emission was observed after smearing. The mechanically generated smeared state recovered so rapidly that characterization of its emission was difficult at room temperature using traditional luminescence techniques. Thus, a new complementary metal oxide semiconductor camera imaging method was developed and used to calculate the decay time of the mechanically generated smeared state (i.e., smeared-state decay; τ) for gbmOMe thin films. Additionally, this method was used to evaluate substrate and film thickness effects on ML recovery for glass and weighing paper films. The recovery behavior of gbmOMe was largely substrate-independent for the indicated matrixes; however, thickness effects were observed. Thus, film thickness may be the main factor in determining ML recovery behavior and must be accounted for when comparing the recovery dynamics of different ML materials. Moreover, when heated above the melting point (T = 119 °C), bulk gbmOMe powders assumed a metastable state that eventually crystallized after a few minutes at room temperature. However, melted thin films remained in an amorphous state indefinitely despite annealing at different temperatures (50-110 °C). The amorphous phase was identified as a supercooled liquid via changing the rate of cooling in differential scanning calorimetry thermograms.

Methoxy‐Substituted Difluoroboron Benzoylacetonate Complexes with Color‐Tunable Phosphorescence

“…The 5 % dye loading spectrum of 1 has a second broader peak at around 470 nm, possibly due to aggregation effects caused by increased dye‐dye interactions. Interestingly, 3 did not show the usual trend of red‐shifted emission with higher dye loading, possibly due to steric effects of the closely positioned methoxy substituents preventing π‐stacking . The fluorescence maxima for all three dye loadings for 3 resided around 440 nm.…”

“…Interestingly, 3 did not show the usual trend of red-shifted emission with higher dye loading, possibly due to steric effects of the closely positioned methoxy substituents preventing p-stacking. [53] The fluorescence maxima for all three dye loadings for 3 resided around 440 nm.…”

Recent Advances in Mechanochromic Luminescence of Organic Crystalline Compounds

“…In 2017, Fraser and coworkers developed a camera method to investigate the self-recovering MCL behavior of thin films prepared from crystalline β-diketone dye 12 (Figure 3f ). 27 The rapid self-recovering process of the thin film was analyzed by the intensity decay of each pixel observed by a video camera. This study revealed the importance of film thickness for selfrecovering MCL as significant fluctuations in recovery behavior were observed for thinnest films.…”

Aggregation‐Induced Emission‐Active Carbazolyl‐Modified Benzo[4,5]thiazolo[3,2‐c]oxadiazaborinines as Mechanochromic Fluorescent Materials

“…On the other hand, tetracoordinated organoboron complexes are intensively investigated as highly emissive luminophores. A large number of O,O-coordinated organoboron complexes based on β-diketone ligands, [13] and N,O-coordinated analogues, based on β-ketoiminate or β-iminoenolate ligands, [14] were studied as promising MFC materials. Nevertheless, despite the great progress, the obtaining of MFC-active organoboron complexes, exhibiting high solid-state photoluminescence quantum yield (PLQY), still remains challenging.…”