Encapsulating electron-rich guest in a MOF host through donor-acceptor interaction for highly tunable luminescence

The rational construction and modulation of charge-transfer based fluorescence materials in host-guest systems by virtue of donor-acceptor interactions remains a challenge owing to the elaborate self-assembly process of acceptor and donor components. Taking into account the design principles of the host-guest system, a welldefined MOF with electron-deficient properties should be an ideal host for the building of charge-transfer based fluorescence materials. Herein, an electron-deficient MOF host, [Cd3(NDC)3(tpt)2(H2O)3] (1) (H2NDC = 1,4-naphthalenedicarboxylic acid, tpt = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine), and a corresponding series of host-guest materials 1 superset of guest (guest = phenanthrene for 2, anthracene for 3, pyrene for 4, triphenylene for 5) with charge-transfer based fluorescence were successfully fabricated via the donor-acceptor interactions. Profiting from the clear electron-rich guests to electron-deficient MOF framework charge transfer interactions, the host-guest materials exhibit color-tunable emission over a wide range by rational selection of guest molecules. Furthermore, the electronic structure calculations reveal that the multicolor emission of the newly synthesized MOF materials depends on the HOMO energy level/ionization potential of guests. This work provides a hopeful strategy for the assembly of various novel charge transfer fluorescent materials as potential luminophores.

Automated summary

The rational construction and modulation of charge-transfer based fluorescence materials in host-guest systems remains a challenge. In this study, a well-defined MOF host with electron-deficient properties was successfully used to fabricate host-guest materials with charge-transfer based fluorescence. By selecting guest molecules, the emission color can be tuned over a wide range. This work provides a hopeful strategy for the assembly of various novel charge transfer fluorescent materials.