Yellow and Orange-Red Room-Temperature Phosphorescence from Amorphous Nonaromatic Polymers

Many nontraditional luminogens (NTLs) without any large & pi;-conjugated structures are reported to exhibit room-temperature phosphorescence (RTP). Unfortunately, the reported NTLs mostly emit blue or green RTP. Achieving more redshifted RTP from NTLs remains a great challenge. Herein, a series of nonaromatic polymers exhibiting yellow and orange-red RTP are reported. Poly(itaconic anhydride) (PITA) does not exhibit RTP, its hydrolyzed product poly(itaconic acid) (PITAc) exhibits weak yellow RTP, but the ionized product poly(sodium itaconate) (PITANa) can emit stronger and redshifted RTP. Moreover, the ionized copolymers poly(vinyl pyrrolidone-co-sodium itaconate) (PIVPNa) and poly(vinyl pyrrolidone-co-sodium maleate) (PMVPNa), the mixture of PITANa/poly(vinyl pyrrolidone) (PVP), and the full hydrolyzed product of poly(vinyl caprolactam-co-sodium itaconate) (PIVCNa) all exhibit strong orange-red RTP emissions at & AP;600 nm. Structural characterizations and theoretical calculations prove that hydrogen bonding and ionic bonds lead to the rigidification of polymer chain conformations, and more importantly, both intra- and interchain nonaromatic electron donor-acceptor (nDA) structures and hence through-space charge transfer are formed between carboxylate and lactam groups in proper conformations, which facilitates the occurrence and redshift of RTP in NTLs. This work provides a novel strategy to design NTLs with redshifted RTP and improves the understanding of the photoluminescence mechanism of NTLs.