Here, we report three new TADF donor-acceptor emitters with a triphenylamine (TPA) donor and nitrogen-containing heterocyclic pyrazine-based acceptor, 4 [2',3':5,6]pyrazino [2,3-f] [1,10]phenanthrolin-12-yl)aniline (TPAPyBPN) (Figure ). Theoretical and experimental results demonstrate that the electron-withdrawing strength of the acceptor increases with both the increased conjugation of the acceptor and the number of nitrogen atoms contained within, leading to a red-shift of the emission within the series. These nitrogen atoms can also act as ligands for metal binding and the resulting change in photophysics can be exploited in metal ion sensing. We found that these compounds exhibited a stark spectral response to the detection of ZnCl2, due to the formation of zinc chlorido complexes. Of these three emitters, TPAPyBP showed the most dramatic and fast fluorescence response toward ZnCl2 by shifting emission from green (550 nm) to deep red (680 nm). We separately explored these compounds as emitters in OLEDs and documented a rather large host polarity-induced shift in the emission from films doped in 4,4′bis(N-carbazolyl)-1,1′-biphenyl (CBP) to 2,8-bis(diphenyl-phosphoryl)-dibenzo[b,d]thiophene (PPT). In particular, the OLEDs with TPAPyBPN in PPT emitted at 657 nm and showed an EQEmax 12.5%. This electroluminescence was 61 nm red-shifted in comparison to a device fabricated in CBP host (λEL= 596 nm, EQEmax = 13.6%), without significant loss in efficiency. The devices with TPAPyAP and TPAPyBP doped in CBP emitted at λEL= 526 nm with EQEmax = 7.6% and λEL= 558 nm with EQEmax = 9.1%, respectively.