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 Jaggregate contribution in the former.Since John and Clar's synthesis of pentacene in the early 1930's, [1] the synthetic strategies and properties of higher member acenes have challenged chemists. Early on, pentacene and structurally related molecules were of curiosity-driven research; nowadays, pentacene is considered a reference hole semiconductor in organic field-effect transistors. [2] Propelled by such curiosity, boron and nitrogen atoms have been introduced into π-backbones of poly-aromatic hydrocarbons, structurally similar to their hydrocarbon analogues, resulting in interesting heteroarene molecules showing different properties. [3] Azapentacenes are, thereby, a particularly interesting subgroup of these heteroarenes, [3a] which formally result from inserting nitrogen atoms into the pentacene skeleton; such interest mainly arose from the promise of tuning the electronic structure, molecular packing, stability, and processability of pentacene by replacing C atoms with N atoms of varied number, position and valence state. [4] Synthetic routes to prepare azaacenes often use condensation/alkynylation methods that have been developed for the preparation of all-carbonacenes. [5] Known N-quaternized azaacenium salts were synthesized by N-alkylation of azapentacenes or by introducing aryl groups into the precursors of azaacenes. [6] N,N'-dihydro compounds, which may be obtained by reduction of larger azaacenes, are known for much longer time, and found more stable than longer azaacenes themselves. [7] Aggregation induced emission (AIE) and AIE-luminogen systems are, at the moment, topics of high interest and impact due to the increment of the emission properties in aggregate systems, which are usually poorly emissive. The occurrence of AIE with a new fluorescence band originating from intermolecular interactions was first reported by Scheibe et al. [8] and Jelley [9] who independently observed in 1936 an unusual behavior for pseudoisocyanine chloride (also known as 1,1'diethyl-2,2'-cyanine chloride, PIC chloride) whereas in aqueous solutions the absorption maximum...
