科研成果

A molecule featuring two distinct cooperatively grown J-aggregates is investigated. Interestingly, when cooling a hot monomer solution, the thermodynamically less stable J1 is exclusively formed even at a particularly slowed temperature dropping rate, which transforms to the more stable J2 at room temperature with very slow kinetics. This observation is ascribed to the differed nucleus sizes of J1 and J2 . During the cooling process, smaller J1 nuclei are formed first at a higher temperature, favored by the entropy effect. At intermediate temperatures, the elongation of J1 out-competes the nucleation of J2 . Then, below the elongation temperature of J2 , the formation of this thermodynamically stable aggregate is hindered kinetically, due to the depletion of monomer by the slow dissociation of J1 . Additional evidence proving the larger nucleus size of J2 is also identified with the varied-temperature spectral analyses and mathematic simulations.

Polycyclic aromatic hydrocarbon (PAH) structures with suitable electron-withdrawing groups are useful building blocks for developing optical and electron-transporting materials. Here, we report the application of double benzannulation processes to synthesize PAH diimides with enlarged π-frameworks featuring a central anthracene moiety. The processes are realized by copper-catalyzed [4+2] cycloaddition of ethynyl-substituted aromatic dicarobximide to 2,5-bis(phenylethynyl)terephthalaldehyde, followed by intramolecular photocyclization or direct arylation via Heck cross coupling. Specifically, A central symmetric benzo[1,2- k :4,5- k ']-bis(fluoranthene)-3,4,12,13-tetracarboxyl diimide (BFDI) is acquired, with a single crystal revealing its completely planar polycyclic skeleton. Such a shape-persistent PAH expectedly exhibits a tendency to stack face-to-face and forms J-aggregates. Moreover, BFDI can be expediently difunctionalized site-selectively in reactive 9 and 10 positions of the anthracene unit and applied to prepare conjugated polymers. When coupled with 1,4-diketopyrrolo[3,4- c ]-pyrrole (DPP) via thiophene and dithiophene linkers, two significantly broadened absorption bands extended to the near-infrared regime appear, evidencing the effective π-conjugative extension ability of BFDI unit.