Comparison of Carbazole and Fluorene Donating Effects on the Two‐Photon Absorption and Nitric Oxide Photorelease Capabilities of a Ruthenium–Nitrosyl Complex

• Published in: European journal of inorganic chemistry 2018-01, Vol.2018 (3-4), p.531-543
• Main Authors: Enriquez‐Cabrera, Alejandro, Lacroix, Pascal G., Sasaki, Isabelle, Mallet‐Ladeira, Sonia, Farfán, Norberto, Barba‐Barba, Rodrigo M., Ramos‐Ortiz, Gabriel, Malfant, Isabelle
• Format: Article
• Language: English
• Subjects: Carbazoles; Charge transfer; Crystal structure; Density functional calculations; Drug delivery; Electronic structure; Inorganic chemistry; Nitric oxide; Nitrogen dioxide; Nitrogen oxides; Photochemistry; Photon absorption; Ruthenium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201700895

A ruthenium–nitrosyl derivative of formula [RuII(CzT)(bipy)(NO)](PF6)3 [CzT = 4′‐(N‐ethylcarbazol‐3‐yl)‐2,2′:6′,2′′‐terpyridine, bipy = 2,2′‐bipyridine] has been synthesized and fully characterized, and compared with the previously reported [RuII(FT)(bipy)(NO)](PF6)3 complex [FT = 4′‐(9,9‐dihexyl‐9H‐fluoren‐2‐yl)‐2,2′:6′,2′′‐terpyridine]. Additionally, the X‐ray crystal structure of [RuII(CzT)(bipy)(NO2)](PF6), the precursor of [RuII(CzT)(bipy)(NO)](PF6)3, is reported. The presence of a tertiary amine in the carbazole unit leads to redshifted charge‐transfer transitions towards the electron‐withdrawing Ru–NO fragment and hence enhanced two‐photon absorption (TPA) properties. In contrast, the quantum yield of the NO· photorelease process is lower for the carbazole‐containing complex. The issue of optimization of the TPA versus NO·‐release capabilities is addressed. Replacing a fluorene by a more donating carbazole unit in a ruthenium–nitrosyl complex leads to a decrease in the quantum yield of NO photorelease from 0.03 to 0.01, and to an increase in the two‐photon cross‐section from 108 to 159 GM. This raises the issue of the optimization of the donating/withdrawing effect on the encaging cross‐section.