Amplified spontaneous emission, optical waveguide and polarized emission based on 2,5-diaminoterephthalates

Morphological Evolution of Strongly Fluorescent Water Soluble AIEEgen-Triblock Copolymer Mixed Aggregates with Shape-Dependent Cell Permeability

Dimethyl-2,5-bis(4-methoxyphenylamino)terephthalate (DBMPT) is a water-insoluble fluorogenic molecule, which has been rendered water-soluble in physiological conditions, by the addition of triblock copolymers (TBPs), P123 (PEO₁₉PPO₆₉PEO₁₉), and F127 (PEO₁₀₀PPO₆₅PEO₁₀₀). DBMPT-TBP mixed aggregates, formed in the process, exhibit significant aggregation-induced enhancement of emission, with nanosecond fluorescence lifetimes. Dynamics involved in suppression of nonradiative pathways and consequent enhancement of fluorescence are followed by femtosecond transient absorption and time-resolved fluorescence spectroscopic techniques. Interestingly, shapes of the aggregates formed with the two TBPs are found to be very different, even though they differ only in the length of hydrophilic blocks. DBMPT-P123 aggregates are micrometer-sized and spherical, while DBMPT-F127 aggregates form nanorods. Evolution of their morphologies, as a function of TBP concentration, is monitored using cryo-TEM, FESEM, and fluorescence lifetime imaging microscopy. Fluorescence lifetime distribution provides useful insight into microheterogeneity in these mixed aggregates. Excellent cell permeability is observed for DBMPT-F127 nanorods, in contrast to DBMPT-P123 microspheres. These fluorescent nanorods exhibit the ability to mark lipid droplets within the cell and hence bear the promise for application in intracellular imaging.

Exceptionally Plastic/Elastic Organic Crystals of a Naphthalidenimine-Boron Complex Show Flexible Optical Waveguide Properties

The design of molecular compounds that exhibit flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multidimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine-boron complex that showed size-dependent dual mechanical bending behavior whereas its parent Schiff base was brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Furthermore, the luminescence of the molecule was turned-on subsequent to boron complexation, thereby allowing it to be explored for multimode optical waveguide applications. Our in-depth study of the size-dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications.

Scale Effect of a Fluorescent Waveguide in Organic Micromaterials: A Case Study Based on Coumarin Microfibers

The classical method for evaluating the waveguide ability only focuses on the optical loss coefficient. However, for the micro- or submicroscale, an organic waveguide is demonstrated by the present study whose scale effect should not be neglected. We found that the optical loss coefficient increased remarkably when decreasing the sectional size of the microfibers. Furthermore, simulations based on Finite-Difference Time-Domain also demonstrated the size-dependent effect of the waveguide. Both the experimental and simulating results showed that the optical loss coefficient converges to a certain value, which means that the scale effect can be neglected as the sectional size is large enough. On the basis of the present study, we suggest that the scale-dependent effect on the sectional size of the waveguide should be investigated by evaluating the waveguide ability by the optical loss coefficient.

Controllably realizing elastic/plastic bending based on a room-temperature phosphorescent waveguiding organic crystal

The room-temperature phosphorescent DBBZL crystals could exhibit reversible bending and irreversible bending based on one crystal. These flexible crystals exhibit good waveguiding property in straight state, elastic bending state and plastic bending state, demonstrating the application of flexibility.

Recently, the study of flexible (elastically bendable and plastically bendable) organic single crystals has become a hot research field in crystal engineering. In general, crystal elasticity and plasticity are incompatible with each other. Different from the applications of fluorescent crystals, the applications of room-temperature phosphorescence (RTP) materials generally ignore the crystallographic nature of large single crystals. Herein, we creatively combine elasticity and plasticity based on one RTP crystal 4,4′-dibromobenzil DBBZL. The in-depth study of the irreversible transformation between elastic bending and plastic bending provided important insights into the mechanism of both elastically bendable crystals and plastically bendable crystals in crystal engineering. The DBBZL crystal exhibits elastic bending (reversible) under external stress, whereas it shows plastic bending (irreversible) after excessive bending. Notably, the first phosphorescent optical waveguides of large single RTP crystals are realized not only in straight state, but also in elastic bent state and plastic bent state.

Elastic Self-Doping Organic Single Crystals Exhibiting Flexible Optical Waveguide and Amplified Spontaneous Emission

Organic crystals are generally brittle and tend to crack under applied stress. Doped organic crystals are even more brittle because of lattice defects. Herein, the first doped organic crystals 1d@2d, which display elastic bending ability under applied stress, are reported. Moreover, the potential applications of elastic-doped crystals 1d@2d in flexible optoelectronics are impressively demonstrated. The elastic crystals 1d@2d with high quality and large size are crystalized by a simple and unique "self-doping" process, which is a regular solution evaporation of crude product 1d (2,5-dihydro-3,6-bis(octylamino)terephthalate) containing a minute amount of 2d (3,6-bis(octylamino)terephthalate) as the oxidized byproduct. The host 1d is easily crystallized to form elastic crystals but is nonfluorescent, while the guest 2d has poor crystallinity and is highly emissive. The doping approach integrates the advantages of both 1d and 2d, and thus endows doped crystals 1d@2d with good elasticity as well as intense orange fluorescence. Taking these advantages, the application potentials of these doped crystals 1d@2d are evaluated by measuring optical waveguide and amplified spontaneous emission in both the straight and bent states.