Thiaheptapyrrin and Thiatetrapyrrin Armed p ‐Phenylene‐Bridged Norrole as NIR‐II Dyes: Photothermal Behavior Effectively Enhanced by Protonation and Deprotonation
Che Yang, Hangchong Lu, Yue Xu, Zhiyang Zhang, Yuanjun Lu, Run Li, Glib Baryshnikov, Chengjie Li, Hans Ågren, Hua Lu, Qizhao Li, Yongshu XieABSTRACT
To extend the absorption spectra of p ‐phenylene‐bridged norroles with the absorption peaks below 700 nm ( 1 and 2 ) and probe the photothermal applications in the near‐infrared region, cyclization of thiaheptapyrrin ( 3 ) afforded a p ‐phenylene‐bridged norrole armed with a thiatetrapyrrin side chain ( 4 ) in a 52% yield. Compared to 1 and 2 , 4 demonstrates a much narrower HOMO–LUMO gap and considerably red‐shifted absorption spectrum tailing to ca . 1150 nm, which may be related to its extended molecular structure. Interestingly, the absorption spectra of both 3 and 4 can be considerably intensified and red‐shifted into the near‐infrared II region upon protonation and deprotonation. On this basis, photothermal conversion behavior was investigated by irradiating 20 µM solutions with a 1064 nm laser for 10 min. Thus, 3 and 4 exhibited high photothermal conversion efficiencies (PCEs) of 64.5% and 58.9% with temperatures rising to 48.5°C and 36.0°C, respectively. Notably, under identical illumination conditions, protonated and deprotonated forms of 3 demonstrated higher temperature rise to 73.8°C and 77.7°C, respectively. Meanwhile, 4 also shows similar behavior upon protonation and deprotonation. This work provides insights into designing NIR‐II photothermal agents by synthesizing long chain oligopyrrins and p ‐phenylene‐bridged norroles in combination with supramolecular means like protonation and deprotonation.