[4 + 2] Cycloaddition Reaction To Approach Diazatwistpentacenes: Synthesis, Structures, Physical Properties, and Self-assembly

Three novel diazatwistpentacenes
(1,4,6,13-tetraphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene
(1, IUPAC name: 9,11,14,16-tetraphenyl-1,6-dihydrobenzo­[8,9]­triphenyleno­[2,3-g]­phthalazine); 1,4-di­(pyridin-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene
(2, IUPAC name: 9,16-diphenyl-11,14-di­(pyridin-2-yl)-1,6-dihydrobenzo­[8,9]­triphenyleno­[2,3-g]­phthalazine); and 1,4-di­(thien-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene
(3, IUPAC name: 9,16-diphenyl-11,14-di­(thien-2-yl)-1,6-dihydrobenzo­[8,9]­triphenyleno­[2,3-g]­phthalazine)) have been successfully synthesized through
[4 + 2] cycloaddition reaction involving in situ arynes
as dienophiles and substituted 1,2,4,5-tetrazines as dienes. Their
structures have been determined by single-crystal X-ray diffraction,
confirming that all compounds have twisted configurations with torsion
angles between the pyrene unit and the 2,3-diazaanthrance part as
high as 21.52° (for 1), 24.74° (for 2), and 21.14° (for 3). The optical bandgaps for
all compounds corroborate the values derived from CV. The calculation
done by DFT shows that the HOMO–LUMO bandgaps are in good agreement
with experimental data. Interestingly, the substituted groups (phenyl,
pyridyl, thienyl) in the 1,4-positions did affect their self-assembly
and the optical properties of as-resulted nanostructures. Under the
same conditions, compounds 1–3 could
self-assemble into different morphologies such as microrods (for 1), nanoprisms (for 2), and nanobelts (for 3). Moreover, the UV–vis absorption and emission spectra
of as-prepared nanostructures were largely red-shifted, indicating
J-type aggregation for all materials. Surprisingly, both 1 and 2 showed aggregation-induced emission (AIE) effect,
while compound 3 showed aggregation-caused quenching
(ACQ) effect. Our method to approach novel twisted azaacenes through
[4 + 2] reaction could offer a new tool to develop unusual twisted
conjugated materials for future optoelectronic applications.