Photobasic transition-metal complexes

• Published in: Coordination chemistry reviews 2024-01, Vol.498, p.215441, Article 215441
• Main Authors: Bysewski, Oliver, Sittig, Maria, Winter, Andreas, Dietzek-Ivanšić, Benjamin, Schubert, Ulrich S.
• Format: Article
• Language: English
• Subjects: Acid-base reaction; Excited-state lifetime; Photobase; pKa value; Transition-metal complexes
• ISSN: 0010-8545; 1873-3840
• DOI: 10.1016/j.ccr.2023.215441

[Display omitted] •Transition-metal complexes can act as photobases due to increased excited-state pKa values.•One might use Förster-cycle analysis and/or pH-dependent luminescence titration to determine pKa and pKa* values.•Ru(II)–polypyridyl complexes have widely been studied regarding their acid-base reactions in the ground state and excited state.•The ligand design, i.e., choice and positioning of the (photo)basic group, the type of coordination (homoleptic vs. heteroleptic) as well as the choice of the photoactive metal are of great importance.•Fundamental knowledge on how to control the excited-state basicity of complexes has been gained, but practical applications are not yet at hand. Transition-metal complexes, which exhibit photobasic properties, are highly promising for chemical applications where the proton abstraction represents one key step. Photobases feature an increased basicity in the excited state and, in particular, molecules which offer this property upon excitation with visible light are highly attractive. This criterium is met by transition-metal complexes which bear a basic substituent. Due to a metal-to-ligand charge transfer (MLCT), electron density in the substituent is increased – it becomes more basic. In here, we would like to elaborate the concept of photobases at the example of transition-metal complexes and provide an overview of the up-to-now available literature.