Synthesis and luminescent properties of the bipyridine derivative with a D-A-A structure

A donor-acceptor1-acceptor2 (D-A1-A2) pyridine derivative (P263) was designed and synthesized. The theoretical calculations showed that the mixed character of the locally excited (LE) and intramolecular charge transfer (ICT) in the T n states could be beneficial to achieve high spin-orbit coupling (SOC) values, thereby promoting efficient intersystem crossing (ISC). The fluorescence emission spectra of P263 exhibited an obvious solvent-dependent emission behavior, which was attributed to the effective ICT through the introduction of dual acceptor units. In addition, the protonation/deprotonation processes of the nitrogen atoms in the pyridine units induced the alterations in the emission spectra, rendering P263 a fluorescent sensor for proton ( H + ) detection. Moreover, the pyridine units could form the hydrogen-bonding interactions with the poly(vinyl alcohol) (PVA) matrix, which was favorable for the suppression of the nonradiative decays and the stabilization of the triplet excitons. The obtained P263@PVA film through doping P263 into PVA showed room-temperature phosphorescence (RTP) properties with a long lifetime of 535 ms and the quantum yields of 3.62 %.