Ultrafast excited state dynamics and light-switching of [Ru(phen)2(dppz)]2+ in G-quadruplex DNA

• Published in: Communications chemistry 2021-05, Vol.4 (1), p.68-10, Article 68
• Main Authors: Yang, Chunfan, Zhou, Qian, Jiao, Zeqing, Zhao, Hongmei, Huang, Chun-Hua, Zhu, Ben-Zhan, Su, Hongmei
• Format: Article
• Language: English
• Subjects: 639/638/440/56; 639/638/440/949; Charge transfer; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Coordination compounds; Dynamics; Excitation; Ligands; Luminescence; Ruthenium; Spectroscopy; Spectrum analysis; Water chemistry
• ISSN: 2399-3669; 2399-3669
• DOI: 10.1038/s42004-021-00507-0

The triplet metal to ligand charge transfer ( 3 MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with 3 MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the 3 MLCT relaxation dynamics of [Ru(phen) 2 (dppz)] 2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the 3 MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from 3 MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen) 2 (dppz)] 2+ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications. Photoactive ruthenium metal complexes are relevant luminescent DNA markers, but deciphering their local excited state dynamics in complex biochemical environments is challenging. Here the authors combine femtosecond and nanosecond pump-probe spectroscopy to elucidate the local hydration effects and 3 MLCT relaxation dynamics of [Ru(phen) 2 (dppz)] 2+ in two G-quadruplexes.