Multifunctional stimuli-responsive materials with room-temperature phosphorescence (RTP) has been demonstrated to be one of the most important members of the stimuli-responsive material family and their development remains a great challenge at this stage. Herein, we successfully synthesized two coordination polymers (CPs), formulated as {[M(cbbpy)(HBTC)(H₂O)]·2H₂O}_n (M = Zn (1) and Cd (2)), using a viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy) and trimesic acid (H₃BTC) by tuning different metal ions. Complexes 1 and 2 show excellent chromic behavior in response to X-ray and UV light. In particular, complex 1 exhibits thermochromism. Moreover, complexes 1 and 2 exhibit dual fluorescence and RTP emissions in the solid state, emitting yellow afterglow of 1.5 s and 1 s at room temperature (297 K) and cyan afterglow of 6.5 s and 5 s at a low temperature (77 K), respectively, when turning off the UV lamp. A hypothetical mechanism is proposed via theoretical calculations that the fluorescence corresponds to the transfer of electrons from the viologen-based moiety to O1 and O2 of complexes. And the phosphorescence corresponds to the intersystem crossing (ISC) process with electrons being transferred from the viologen moiety through the metal atom to the carboxyl group of trimesic acid in an excited triplet state and then transition back to the ground state. In addition, multiple encryption and anti-counterfeiting were successfully designed through photochromism, fluorescence and RTP of these complexes. This work not only provides a new strategy for the design and synthesis of multifunctional materials, but also develops a new dynamic photo-controlled afterglow switching.

Boron-based clusters with hypercoordinate centres are chemically unstable due to the electron-deficiency of the exposed boron atoms. We propose to chemically stabilize such clusters by electronically compensating the boron atoms via dative π bonds.

Realization of planar tetracoordinate arrangements of nitrogen atoms is challenging because their preference for localized bonding (caused by its high electronegativity) makes them typically tricoordinate. This is especially true for the more electronegative oxygen atoms. Herein, we computationally designed two clusters NBe4H4− and OBe4H4; they contain a planar tetracoordinate nitrogen (ptN) and planar tetracoordinate oxygen (ptO) atom, respectively. Remarkably, the former is a dynamically stable global minimum, while the latter is not. The bonding analysis proves that planar tetracoordination in NBe4H4− favors over tricoordination because of the presence of multicenter delocalized bonds. In contrast, the planar tricoordination dominates due to its weak delocalized bonding ability of oxygen in the OBe4H4 cluster. Moreover, the 6σ/2π double aromaticity due to multicenter delocalized bonds allows the NBe4H4− cluster to obtain additional stability. This cluster is a promising synthetic due its dynamic and thermodynamic stability.