In solid states, molecular polarization of donor-acceptor (D-A) molecules is basically implemented via external polarizing source (e. g., electric field). Inside-system chemical polarization approaches that can be smart and low cost are less concerned, but they are desirable for achieving stable but distinct molecular photophysical properties. The main challenge issue is due to the difficult control of charge-separation orientation in solid states.
Recently, Zhu’s group developed a series of D-A molecules with both proton donor and acceptor involved were designed. Water molecular bridge was then established in their crystal structures, which firmly and alternately connected with the proton donor of one molecule and the acceptor of the other via intermolecular H-bond network. In this way, selective dual polarization of the phenolic hydroxyl group and the pyridinyl group could be achieved, owing to the strengthening of charge-separation orientation upon the simultaneous deprotonation and protonation tendency of the D-A molecules. This effect led to an up to 3-5 folds amplification of the molecular dipole moments in the crystal form relative to their monomeric state. On this basis, multi-excitation and multi-emission characteristics from these charge-separated crystals were achieved, endowing the ability of visually detecting the energy of light source covering a large-scale UV-Vis spectral region.
This work provides a practical chemical approach for developing intrinsically polarized systems that can exhibit stable but distinct molecular photophysical properties, and may also inspire more advanced and sophisticated approaches for fabricating solid-state materials with distinct optoelectronic properties. This work has been published on the journal of Chemical Science with a Master candidate, Ms. Yi Xing as the first author and Professor Liangliang Zhu as the corresponding author. DOI: 10.1039/D2SC00908K.
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