Guest molecules may endow porous materials with new or enhanced properties as well as functions. Here, a porous hydrogen-bonded organic framework (HOF) constructed from a three-armed triphenylamine derivative is used to investigate how guests regulate photoluminescence and trigger force-stimuli response. It was found that guest solvents in pores might regulate HOF's luminescence. Interestingly, acetic acid as a guest endowed HOF materials with longer emission wavelengths and triggered the responses to mechanical force stimuli. Under shear force, an obvious blueshift in emission spectra was observed because of the loss of free guests and the conversion of πstacking model. Further blue-shifted emission appeared while the bound guests were completely removed by heating. Mechanofluorochromic HOF materials could be regenerated through recrystallization and adsorbing guest. Conversely, HOFs with other guests and activated HOFs only resulted in a slight change in their fluorescence behaviors after force stimuli.
A dumbbell-shaped compound (TPAD) with four 2,4-diaminotriazine moieties as H-bond units and a benzene ring as a bridge group was found to form hydrogen-bonded organic frameworks (HOFs) with strong cyan fluorescence. An energy acceptor, 6,6′,6″, 6‴-(((benzo[c][1,2,5]thiadiazole-4,7-diylbis-(4,1phenylene))bis(azanetriyl))tetrakis(benzene-4,1-diyl))tetrakis-(1,3,5-triazine-2,4-diamine) (BTAD), with the same molecular skeleton as TPAD and a longer emission wavelength could homogeneously distribute within the framework of TPAD through occupying the locations of TPAD. As a result, two-component HOFs (TC-HOFs) were formed. The nonradiative energy transfer from TPAD as the donor to BTAD as the acceptor happens within frameworks owing to the efficient spectral overlap between the emission of TPAD and the absorption of BTAD. Moreover, the emission wavelengths and colors of TC-HOFs could be easily and continuously modulated by the content of the acceptor. The fluorescence color changed from cyan to orange when the content of BTAD gradually increased. This finding affirms that TC-HOFs with continuously adjustable composition can be constructed from two molecules with the same molecular skeleton, and highly efficient nonradiative energy transfer may happen in porous TC-HOFs. To the best of our knowledge, these TC-HOFs are the first example of TC-HOFs involved in energy transfer.
A phenothiazine derivative was found to exhibit multicolour- and high-colour-contrast switching in response to force and acid vapour by introducing an asymmetric D–π–A–π–D structure.
Hydrogen
bond-induced π-stacking conversion was used to achieve an enhanced
force-stimuli response of 9,10-bis(2-(pyridin-4-yl)vinyl)anthracene
(BP4VA). In BP4VA crystals, the molecules adopted a J-aggregate pattern,
and no overlap between the central anthracene planes was observed.
Trimesic acid (TA) as a hydrogen bond donor could promote the transformation
of the π-stacking type of BP4VA as a hydrogen bond acceptor.
It was found that TA and BP4VA molecules formed two-dimensional lamellar
hydrogen-bonded frameworks with large windows, which were filled by
BP4VA molecules belonging to other layers. Within such three-dimensional
packing, J-aggregate stacking type of BP4VA converted into a mixture
of J-type and H-type dimers. Moreover, BP4VA adopted a highly twisted
conformation, and π–π interaction between them
was very weak. So, the hydrogen-bonded complex emitted a short wavelength
fluorescence. More importantly, the yellow hydrogen-bonded complex
turned into red solids under force stimuli, and its fluorescence had
a fairly large shift of more than 110 nm. This is in contrast with
a spectral shift of 43 nm from the sheared neat BP4VA crystals. Quantum
chemical calculation and spectral observations implied that the planarization,
shortened π-distance, and large overlap between anthracence
units should be responsible for the large spectral shift. The results
imply that the appropriate acid as a hydrogen bond donor might help
distyrylanthracene derivatives possess outstanding functions.
Two phenothiazine derivatives with electron-withdrawing cyano and ester groups emitted longer wavelength fluorescence and exhibited different mechanochromic behaviors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.