Tunable Fluorescence in Two-Component Hydrogen-Bonded Organic Frameworks Based on Energy Transfer

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-(4,1-phenylene))­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.