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Smart materials with ultralong phosphorescence are rarely investigated and reported. Herein we report on a series of molecules with unique dynamic ultralong organic phosphorescence (UOP) features, enabled by manipulating intermolecular interactions through UV light irradiation. Our experimental data reveal that prolonged irradiation of single-component organic phosphors of PCzT, BCzT, and FCzT under ambient conditions can activate UOP with emission lifetimes spanning from 1.8 to 1330 ms. These phosphors can also be deactivated back to their original states with short-lived phosphorescence by UV irradiation for 3 h at room temperature or through thermal treatment. Additionally, the dynamic UOP was applied successfully for a visual anti-counterfeiting application. These findings may provide unique insight into dynamic molecular motion for optical processing and expand the scope of smart-response materials for broader applications.

The structural and photophysical properties of tetradentate Pt(ppzOppz), Pt(ppzOpopy), Pt(ppzOczpy), and Pt(czpyOczpy) have been experimentally and theoretically explored. Single-crystal diffraction measurements provided accurate structural information. Electrochemical and photophysical characterizations revealed internal electronic energy levels in ground and excited states. (Time-dependent) Density functional theory calculation revealed electron distributions in transition processes of S → S and S → T → S. Electronic transition study indicated that Pt(ppzOppz) demonstrated mixed MLCT/LC states and Pt(czpyOczpy) showed MLCT-dominated states in S and T. Both Pt(ppzOpopy) and Pt(ppzOczpy) presented strong delocalized spin transition (DST) during intersystem crossing. Upon frame modification of Pt(ppzOczpy), we found that their S and T can be independently manipulated. These blue emitters showed a tunable and narrow emission band (the narrowest fwhm was 19 nm) with luminescence efficiency as high as 86%. The findings of the DST transition mode in the neutral Pt(II) complexes provide guidance for rational design of novel phosphorescent materials.

and optoelectronic devices. [5,6] Chelated Ir(III) and Pt(II) complexes can acquire high spin-orbit coupling effects, thereby ideally suiting for phosphorescent organic light-emitting diodes (PhOLEDs). [7-9] These complexes can efficiently harness both singlet and triplet excitons and afford 100% internal quantum efficiency in electroluminescent devices. [10,11] Ir(III) complexes are in octahedral-field structure and chelated with three monoanionic bidentate ligands with high-lying π* orbitals, leading to efficient spin-flip triplet transition in metal-to-ligand charge transfer (3 MLCT) characteristic at ambient condition. [12,13] On the other hand, tetradentate square-planar Pt(II) complexes have received considerable attention in terms of their high efficiency, [14,15] stability [16,17] and color purity [18,19] in electroluminescent devices. Recent studies on those Pt(II) complexes revealed highly admixed triplet configurations interacting among regional substates, which dominate the emission in photo-and electroluminescence. [20-23] Furthermore, due to their environmentsensitive property in the lowest triplet excited state (T 1), the emission spectra of the complexes are manageable according to certain circumstance. [24] Bearing in mind the nature of the Pt(II) complexes, we infer it is possible to tune the emission from narrow blue to broad white via triplet managing, [22] which is concurrently challenging in molecular design and desirable in display and lighting applications. Unlike the Ir(III) complexes in closed octahedral geometry, Pt(II) chelated molecules have open square-planar structures, thus are easy to have inter-and intra-molecular excited-state perturbation, such as d 8 …d 8 (Pt…Pt), π…π, and hydrogen bond. [25,26] Generally, Pt…Pt interaction leads to a new metalmetal-to-ligand charge transfer (MMLCT) transition state involving a filled Pt…Pt antibonding orbital and a high-lying π* orbital on the ligand. [27,28] Their semiconducting and longwavelength luminescent properties can be utilized for fabricating high-performance light-emitting field-effect transistors and near-infrared OLEDs. [5,29] Molecular stacking via π-π and hydrogen bonds could also form excimer, giving new emissions in lower energy band. [21] However, the luminescent color A new class of tetradentate Pt(II) complexes, Pt(pzpyOczpy-iPr) and Pt(pzpyOczpy-mesi), enabling fabrication of deep-blue and white phosphorescent devices, is successfully synthesized and fully characterized. Their photoluminescent quantum yields in dichloromethane are over 90% with short decay lifetimes less than 4.0 µs. Under low doping concentration, the emission is governed by ligand-centered triplet transition state (3 LC, 3 π cz *→π cz) on carbazole group, rendering narrow blue emission with full width at half-maximum (FWHM) less than 45 nm. When increasing the doping concentration, expanded monomeric and excimeric emissions are demonstrable, displaying broad white emission with FWHM up to 152 nm. Devices fabricated with 2 wt% dopant in DPEPO host achiev...

Three Pt­(II) complexes, Pt­(czpyOczpy), Pt­(czpyOczpy-Me), and Pt­(czpyOczpy-OMe), are designed to elucidate the inherent relationship between electronically excited-state and photo- and electroluminescent properties. These complexes showed a blue-shifted phosphorescence with a narrowing spectral profile, which are interrelated with the variation of T1 states from the 3MLCT, hybridized 3(MLCT/LC) to 3LC transition. This change is ascribed to the destabilization of LUMO energy levels on the pyridinyl site, leading to more electron distribution on the carbazolide unit in T1. Moreover, the solution-processed device of Pt­(czpyOczpy-OMe), featuring a 3LC transition, shows the best color purity of blue light. Compared to the device of Pt­(czpyOczpy) with 3MLCT character, the device of Pt­(czpyOczpy-Me) with hybridized 3(MLCT/LC) exhibits improved color purity and external quantum efficiency (10.2%) at a luminance of 1000 cd/m2. Therefore, this work gives a mechanistic interpretation of the phosphorescent properties of tetradentate Pt­(II) complexes derived from the manageable lowest triplet excited states.