jp7b01711_si_001.pdf (3.01 MB)
Protonation-Induced Room-Temperature Phosphorescence in Fluorescent Polyurethane
journal contribution
posted on 2017-05-22, 00:00 authored by Wei Sun, Zhaowu Wang, Tao Wang, Li Yang, Jun Jiang, Xingyuan Zhang, Yi Luo, Guoqing ZhangRoom-temperature
phosphorescence (RTP) from purely organic systems
is of practical importance in biological imaging, oxygen sensing and
displaying technologies. The key step to obtaining RTP from organic
molecules is efficient intersystem crossing (ISC), which is usually
low compared to inorganic materials. Here we show that protonation
of a dye molecule, a thioflavin derivative, in strongly polar polyurethane
can be used to effectively harness RTP. Prior to protonation, the
predominant transition is π–π* for the polymer,
which has nearly undetectable RTP due to the large singlet–triplet
energy splitting (0.87 eV); when Brønsted acids are gradually
added to the system, increasingly strong RTP is observed due to the
presence of a new intramolecular charge-transfer state (ICT). The
ICT state serves to lower the singlet–triplet energy gap (0.46
eV). The smaller gap results in more efficient ISC and thus strong
RTP under deoxygenated conditions. The thioflavin–polyurethane
system can be tuned via proton concentration and counterions and opens
new doors for RTP-based polymeric sensors and stimuli-responsive materials.