Polymorphism-Dependent Dynamic Ultralong Organic Phosphorescence

Abstract

Developing ultralong organic phosphorescence (UOP) materials with smart response to external stimuli is of great interest in photonics applications, whereas the manipulation of molecular stacking on tuning such dynamic UOP is still a formidable challenge. Herein, we have reported two polymorphs with distinct photoactivated dynamic UOP behavior based on a pyridine derivative for the first time. Our experiment revealed that the dynamic UOP behavior including photoactivation and deactivation feature is highly dependent on irradiation intensity and environmental atmosphere. Additionally, given the unique dynamic UOP feature, these phosphors have been successfully applied to phosphorescence-dependent molecular logic gate and timing data storage. This result not only paves a way to design smart functional materials but also expands the scope of the applications on organic phosphorescence materials.

Figure 1

The structure of PyCz and two kinds of crystal of PyCz with different photoactivation UOP speed. (a) Molecular structure of PyCz with two kinds of molecular packing mode. Insets: the fluorescence microscopy images of PyCz-B and PyCz-N with the scale bar of 200 μm. (b) The afterglow photos of PyCz-B and PyCz-N at different photoactivation time with a handheld 365 nm UV lamp (40 mW/cm²) under ambient conditions, and the dashed circles are used to distinguish the samples with low afterglow intensity.

Figure 2

Photophysical properties of PyCz under ambient conditions. (a) Steady-state PL spectra of PyCz-B and PyCz-N before (blue line) and after (red line) long photoactivation (power = 40 mW/cm², time = 10 min) under ambient conditions. (b) The phosphorescence spectra and the corresponding peak intensity at 544 nm of PyCz-B and PyCz-N after different photoactivation time ranging from 0 to 10 min by a 365 nm lamp (power = 40 mW/cm²) under ambient conditions. (c) Lifetime decay profiles of the emission peak at 544 nm of PyCz-N and PyCz-B before and after long photoactivation under ambient conditions. (d) The time-phosphorescence mapping of PyCz-B and PyCz-N for 100 min with the 365 nm light source power of 0.67 mW/cm² under ambient conditions. (e) The phosphorescence variation value (I/I₀) at 544 nm during the deactivation of the UOP for PyCz-N and PyCz-B after long photoactivation under ambient conditions. Insets: the corresponding photos at different deactivation time. (f) The corresponding dynamic lifetime τ for the photoactivation by weak 365 nm light (power = 0.67 mW/cm²) and deactivation of PyCz-B and PyCz-N under different atmosphere.

Figure 3

Crystal stacking analysis and simulated calculations for dynamic ultralong organic phosphorescence of PyCz. (a) The intermolecular interactions around one molecule in PyCz-B and PyCz-N before and after long photoactivation in crystalline state measured at 100 K, the green dash line refers to the initial interactions and the red dash line is the added interactions after long photoactivation. (b) The π-π overlap and distance of selected dimer with π-π interactions in PyCz-B(i) and PyCz-N(i). Note that the green isosurface refer to the calculated molecular interactions by IGM, the isovalue is 0.008. (c) The free volume region (cyan isosurface) in single crystal cells of PyCz-B(i) and PyCz-N(i). (d) The calculated change of single molecular energy in PyCz-B and PyCz-N during the process of photoactivation. (e) Proposed mechanism for different dynamic speeds of dynamic UOP in polymorphs.

Figure 4

The demonstration of the application in molecular logic gate. (a) The model of molecular logic gate and the contrast between fluorescence logic gate and phosphorescence logic gate. (b) Under ambient conditions, the photoactivation of PyCz by different power UV light: PyCz-B activated by UV light with the power of 40 mW/cm² and 0.67 mW/cm² (blue line with solid and open circle, respectively), PyCz-N activated by UV light with the power of 40 mW/cm² and 0.67 mW/cm² (red line with solid and open circle, respectively). (c) The truth table for O1 and O2 and the proposed logic gate for PyCz with two inputs and two outputs.