title: Carbazole-based cyano-stilbene highly fluorescent microcrystals.
abstract: 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.
authors.affiliation: Center for Photochemical Sciences, Department of Chemistry, 132 Overman Hall, Bowling Green State University, Bowling Green, Ohio 43403, United States.
authors.forename: Karasinghe A N
authors.initials: KA
authors.lastname: Upamali
authors.forename: Leandro A
authors.initials: LA
authors.lastname: Estrada
authors.forename: Puran K
authors.initials: PK
authors.lastname: De
authors.forename: Xichen
authors.initials: X
authors.lastname: Cai
authors.forename: Jeanette A
authors.initials: JA
authors.lastname: Krause
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Neckers