ORIGINAL ARTICLE Synthesis of Naked-eye Detectable Fluorescent 2H-chromen-2-One 2, 6-Dicyanoanilines: Effect of Substituents and pH on Its Luminous Behavior Rashmi C. Kulkarni 1 & S. Samundeeswari 1 & Farzanabi Shaikh 1 & Nirmala S. Naik 1 & Jyoti M. Madar 1 & Lokesh A. Shastri 1 & Vinay A. Sunagar 2 Received: 30 January 2017 /Accepted: 4 April 2017 # Springer Science+Business Media New York 2017 Abstract A variety of new coumarin derivatives containing C-4 bridged 2,6-dicyanoanilines (4a-4d) were synthesized via multicomponent one pot approach. These novel sensors were characterized by spectral analysis and a series of pH sensing fluorescence studies were performed, the results indicating that the sensors are highly selective and more effective at various pH. The fluorescence colour changes at different pH could be directly detected by naked eyes. Keywords Coumarins . 2,6-dicyanoanilines . Fluorescence pH sensors . Acceptor-donor-acceptor system Introduction In recent years, the design of fluorescent molecular sensors have been flourishing interest in the research and development of pH sensors for monitoring acidity especially in biological [1, 2], material [3, 4], environmental science [5, 6] and other fields, in which the fluorescent pH chemical sensors play a convincing role. The pH values can provide important infor- mation about objects and characteristic nature. Numerous chemical and biochemical analytes (e.g. cations, anions, neu- tral molecules and gases, etc) can be detected by fluorescence [7]. The success of fluorescent sensors can be explained by the distinct advantages offered by its detection in terms of sensi- tivity, selectivity, local observation (e.g. by fluorescence im- aging spectroscopy) and response time etc. [8]. Several fluo- rescence pH sensors have been reported in the literature [9] in which the most widely used techniques are the measurements of fluorescence intensity. In search of a suitable indicator dye for pH sensing, our attention has focused on 2,6-dicyanoanile derivatives [10]. The luminescence investigation of 2,6-dicyanoanilines con- tinues to be an area of inquisition in view of their Acceptor- Donor-Acceptor (A-D-A) system incorporating one electron donor and two electron acceptors [11]. These are excellent fluorophores with relatively high fluorescent quantum yields, Stokes shifts, flexible and tunable physicochemical properties [12]. The promising relevance of these molecules are artificial photosynthesis [13], materials presenting semiconducting or nonlinear optical properties [14] and molecular electronic de- vices [15]. Coumarin itself is not fluorescent, but it exhibits intense fluorescence by various functional groups substitution at 6 and 7 positions [16, 17]. Properly substituted derivatives yield intense fluorescence which are widely used in different branches of chemistry, biology, medicine and physics. These derivatives are an important part of fluorescence probes, sen- sors and switches [18, 19]. The fluorescence of coumarins is widely used as a research tool in polymer science as photo- initiators, fluorescent solar collectors and as reporters of rad- ical reactions [20–22]. Recently, these have been utilized for enantioselective sensing [23]. The fluorescence of coumarin is strongly influenced by substituting the electron-donating or withdrawing groups at some positions or by lengthened π- conjugation [24]. In general, electron-donating substituents Electronic supplementary material The online version of this article (doi:10.1007/s10895-017-2098-y) contains supplementary material, which is available to authorized users. * Lokesh A. Shastri drlashastri@kud.ac.in 1 Department of Chemistry, Karnatak University, Dharwad, Karnataka, India 2 Department of Chemistry, G.S.S. College, Belagavi, Karnataka, India J Fluoresc DOI 10.1007/s10895-017-2098-y