FULL PAPER DOI: 10.1002/ejoc.201500503 Identifying Solid Luminogens through Gold-Catalysed Intramolecular Hydroarylation of Alkynes Aslam C. Shaikh, [a] S. Shalini, [b] Ramanathan Vaidhyanathan, [b] Manoj V. Mane, [c] Ayan Kumar Barui, [d] Chitta Ranjan Patra, [d] Yeduru Venkatesh, [e] Prakriti Ranjan Bangal, [e] and Nitin T. Patil* [a] Keywords: Fluorescence / Luminescence / Solvatochromism / Cell imaging / Dyes/pigments / Gold The identification of a new class of luminogens based on pyr- rolo-quinoxaline embedded coumarin (PQC) structures is re- ported. The reaction relies on the gold-catalyzed hydroaryl- ation reaction of appropriately substituted aryl alkynoates Introduction Luminescent compounds continue to attract intense interest because of their multifaceted use as probes for bio- logical applications and molecular sensors and in optoelec- tronic devices. [1] Usually, organic fluorophores are emissive in solutions but they become nonfluorescent upon aggrega- tion. Tang and co-workers found that some compounds do emit light in the solid state [1d,2] – the phenomenon was referred as aggregation-induced emission (AIE) or aggrega- tion-induced emission enhancement (AIEE). [3] However, the number of materials with AIE/AIEE properties are very limited to date and such compounds are based on only few structural frameworks. [4] Therefore, the identification of structurally novel solid emitters with useful photophysical properties is highly desirable. Recently, we reported a relay [5] catalytic branching cascade (RCBC), a novel technique for accessing new scaffolds in diversity oriented synthesis to produce a variety of polyheterocyclic scaffolds. [6] During the study it was ob- served that many products exhibited weak fluorescence as [a] Organic Chemistry Division, CSIR – National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India E-mail: n.patil@ncl.res.in http:/academic.ncl.res.in/n.patil [b] Department of Chemistry, Indian Institute of Science Education and Research, Pune 411008, India [c] Physical Chemistry Division, CSIR – National Chemical Laboratory, Pune 411008, India [d] Department of Chemical Biology, CSIR – Indian Institute of Chemical Technology, Hyderabad 500607, India [e] Inorganic and Physical Chemistry Division, CSIR – Indian Institute of Chemical Technology, Hyderabad 500607, India Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.201500503. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2015, 4860–4867 4860 that produces molecules that exhibit solvatochromism and aggregation-induced emission enhancement (AIEE) phen- omena. The application of PQCs for live cell imaging has also been demonstrated. the structure became planar and rigid. We envisaged that one of the products obtained from RCBC (cf. P1-OH, Fig- ure 1) would couple with various aryl propiolic acids A to give the corresponding alkynoates, which would undergo metal-catalysed intramolecular hydroarylation reaction to give luminogens. The following approximations were taken into consideration for successful design of the strategy: (1) coumarin-based fluorophores are known in the litera- ture; [7] it is also known that the position of an additional cycle at the coumarin chromophore increases the quantum efficiency in solution. [8] (2) The presence of flat disk-like aromatic molecules at the β-position of the -C=O group will disrupt the planarity, hampering intramolecular rota- tion (IMR), which is the main requirement for the molecule to be a solid emitter. [3] (3) When structures that are cyclic, rigid, and electron-donating (e.g., a nitrogen atom) are attached to the aromatic ring of coumarin the overall push- pull effect is enhanced. Notably, 7-aminocoumarins are well known for exhibiting fluorescence in the solution state; [9] however, to our knowledge, there is only one report on so- lid-state emission. [8a] Recently, Lavis and co-workers mea- sured the increase in quantum yield when the N,N-dimethyl Figure 1. Design of luminescent solid material.