A　new　series　of　fluorogenic　chelating　reagents　based　on　phenylethylidene-3,4-dihydro-1H-quinoxalin-2-one　with　different　substituents　(attached　either　to　the　quinoxaline-2-one　(3)　or　phenyl　ring　(4))　have　been　investigated　to　examine　the　effect　of　the　substituent　(nature/position)　on　the　spectral　properties　and　response　toward　Cu2+　in　the　presence　of　other　metal　cations,　in　ethanol.　It　was　found　that　all　of　the　examined　ligands　exhibit　a　pronounced　response　to　Cu2+　addition　resulting　in　a　red-shift　in　the　UV-vis　spectra　and　a　strong　quenching　in　the　fluorescence　spectra.　Among　the　ligands　examined,　3a　exhibits　the　highest　selectivity　toward　various　metal　cations.　In　general　it　appears　that　the　best　response　selectivity　of　these　ligands　toward　Cu2+　ion　is　obtained　by　either　EDG　in　3　or　EWG　in　4.　For　example,　the　fluorescence　intensity　of　3a　(with　OMe　substituent)　increases　to　about　three　times　that　of　the　unsubstituted　derivative.　(C)　2012　Elsevier　Ltd.　All　rights　reserved.