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J Phys Chem A. 2017 Jun 8;121(22):4225-4232. doi: 10.1021/acs.jpca.7b01711. Epub 2017 May 26.

Protonation-Induced Room-Temperature Phosphorescence in Fluorescent Polyurethane.

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CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China , Hefei, 230026 Anhui, P. R. China.
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , 96 Jinzhai Road, Hefei, Anhui, 230026, P. R. China.
Innovation Center of Chemistry for Energy Materials, Department of Chemical Physics, University of Science and Technology of China , Hefei, 230026 Anhui, P. R. China.


Room-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.


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