Tuning J‐aggregate Formation and Emission Efficiency in Cationic Diazapentacenium Dyes

• Published in: Chemistry : a European journal Vol. 27; no. 29; pp. 7826 - 7830
• Main Authors: Rodrigues, Ana Clara B., Wetterling, Dario, Scherf, Ullrich, Seixas de Melo, J. Sérgio
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 20.05.2021; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: Acetonitrile; Aggregates; AIE; Chemistry; Chemistry, Multidisciplinary; Communication; Communications; Coupling (molecular); Cross coupling; diazapentacene; Dichloromethane; fluorescence; J-aggregates; Nitrogen atoms; Optical properties; photochemistry; Photoluminescence; Photons; Physical Sciences; Salts; Science & Technology; Solvents; Thin films; diazapentacene; J-aggregates; fluorescence; photochemistry; AIE
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202100123

Enhancement of the luminescence efficiency of two new diazapentacenium salts (D1 and D2) of more than 55 for D1 and 22 times for D2) in poor solvents, acetonitrile and/or dichloromethane, was observed and rationalized as formation of emissive J‐aggregates. Both compounds displaying 4‐n‐decylphenyl substituents at the 7,14‐carbons and phenyl (D1) or 2,6‐difluorophenyl (D2) substituents at the quaternary nitrogen atoms in 5,12‐positions have been synthetized in a two‐step procedure involving a two‐fold Buchwald‐Hartwig‐type CN cross‐coupling and an electrophilic Friedel‐Crafts‐type cyclization. The optical properties of the dicationic diazapentacenium salts in various solvents and in thin films have been investigated by steady‐state and time‐resolved absorption and photoluminescence spectroscopies. In thin films and in good solvents, isolated molecules coexist with aggregates. Nonetheless, D1 is seven times more emissive than D2, reflecting a higher J‐aggregate contribution in the former. Two new diazapentacenium salts have been obtained from a new synthetic methodology and shown to display a drastic increase of fluorescence quantum yields induced by aggregation (AIE phenomena) in poor solvents and associated to a particular type of aggregates organization: J‐aggregates. A simple structural modification (4 H in D1 vs 4 F in D2) changes the contribution of J‐aggregates which is quantitatively followed by time resolved fluorescence.