Aggregation-induced enhanced emission (AIEE) is reported for 1-cyano-trans-1,2-bis-(4-carbazolyl)phenylethylene (CN-CPE). The weak luminescence of dilute CN-CPE solutions is enhanced upon aggregate formation into 2-3 μm sized crystals. In contrast to general observations, crystal formation of CN-CPE causes a blue-shift in emission and enhances the intensity. X-ray crystallographic analysis revealed that key factors causing high luminescence efficiency in the crystal are a lack of strong cofacial π-π alignment and the existence of the strong supramolecular interactions due to the intermolecular H-bonding. These factors seem to be responsible for the AIEE phenomenon as molecules of CN-CPE are held in a rigid twisted conformation, thereby increasing the fluorescence intensity in the solid or aggregated states. Accordingly, conformational twisting in the crystal packing process may be responsible for the unusual emission blue-shift in the aggregate.

A novel carbazole-based fluorophore 5-(carbazol-9-yl)-5'-mercapto-2,2'-bithiophene (CBTSH) was synthesized. CBTSH exhibited emission enhancement when attached to the surface of CdSe quantum dots (QDs). The emission quantum yield of CBTSH attached to CdSe is almost 5 times larger than that of CBTSH alone. The emission enhancement of CBTSH on the CdSe surface is due to the restriction on the rotational and vibrational motions of the carbazolylbithienyl unit as a result of QD aggregation.

Heptacene and higher polyacenes have been sought for their high degree of charge carrier mobility in thin film transistors. Such acenes are, however, extremely unstable in ambient conditions. Approaches to obtain stable heptacenes include introduction of suitable substituents, of heteroatoms, or both. Methods to synthesize stable linear and a nonlinear unsubstituted heptacene analogs are discussed. No changes in the UV-visible absorption spectra in solution over time for these materials indicate higher oxidative stability compared to analogous polyacenes.

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