Pentacenequinone derivatives: aggregation-induced emission enhancement, mechanism and fluorescent aggregates for superamplified detection of nitroaromatic explosives

Pentacenequinone derivatives 5-9 have been synthesized by a Suzuki-Miyaura coupling protocol. These derivatives form fluorescent aggregates in mixed aqueous media due to their aggregation-induced emission enhancement (AIEE) attributes. Interestingly, size dependent emission enhancement is observed in the case of derivatives 5-7 and the effect of increase in the number of pyridine rotors on fluorescence emission of pentacenequinone derivatives 6-7 in solution and in the aggregate state confirms that the AIEE phenomenon is at the cost of aggregation driven growth and restriction of intramolecular rotation (RIR). On the other hand, derivatives 8 and 9 having electron rich phenyl groups are donor-accepter-donor type systems which exhibit an intermolecular charge transfer state (ICT) and form fluorescent aggregates in mixed aqueous media. In addition to this, the AIEE characteristics endow pentacenequinone derivatives 5-9 with sensing functionalities such as detection of nitroaromatic compounds. TLC strips of AIEE-active pentacenequinone derivatives 5-9 provide a more convenient and cost-effective approach for the trace detection of nitroaromatic explosives.