Accessing a Long-Lived ³LC State in a Ruthenium(II) Phenanthroline Complex with Appended Aromatic Groups

Abstract

The photophysical properties of a series of heteroleptic Ru(II) complexes of the form [Ru(phen) 2 (phen-5,6-R 2 )] 2+ , where phen = 1,10-phenanthroline and R = phenyl (Ph), p-tert-butylbenzene (p-Ph-tBu), p-methoxybenzene (p-Ph-OMe), and 2-naphthalene (2-naph), have been measured. Variation of the R group does not greatly perturb the electronic properties of the ground state, which were explored with electronic absorption and resonance Raman spectroscopy and are akin to those of the archetypal parent complex [Ru(phen) 3 ] 2+ . All complexes were shown to possess emissive 3 MLCT states, characterized through transient absorption and emission spectroscopy. However, an additional, long-lived excited state was observed in the Ru(II) naphthalene complex. The naphthalene substituents facilitate population of a 40 μs dark state which decays independently to that of the emissive 3 MLCT state. This state was characterized as 3 LC in nature, delocalized over the naphthalene substituted ligand.

Comprehensive Picture of the Excited State Dynamics of Cu(I)- and Ru(II)-Based Photosensitizers with Long-Lived Triplet States

“…A global fit for the most prominent bands of the step-scan difference spectrum (Figures S31–S33) revealed biexponential decays with a dominating long-lived microsecond component contributing to 84–97% for all three systems at 20 K as well as 290 K. For Cubiipo , an impressive lifetime of 439 μs (96%) was observed at 20 K, which is, to the best of our knowledge, among the largest lifetimes reported so far for a Cu­(I) complex. ,,− At 290 K, the corresponding time constant has still a high value of 61.4 μs. In the case of Rubiipo , the lifetime amounts to 197 μs at 20 K and 53 μs at 290 K, values which have only been reported for a very limited number of Ru­(II) complexes so far. − Furthermore, biipo exhibits an excited state lifetime of 201 μs at 20 K and 33.1 μs at 290 K, which are quite high values for an organic molecule. However, the lifetime is clearly below the millisecond lifetimes reached, e.g ., by carbazole, iminidibenzyl, or substituted naphthalene diimides .…”

Merging of a Perylene Moiety Enables a RuII Photosensitizer with Long‐Lived Excited States and the Efficient Production of Singlet Oxygen

“…[ 5 , 7 , 16 , 17 , 18 , 19 ] However, their lack of high extinction coefficients in a broad range of the visible region is a major drawback,[ 19 , 20 , 21 ] which needs to be tackled. One possible solution is the design of multichromophoric architectures containing organic dyes like naphthalene,[ 22 , 23 ] 4 H ‐imidazole,[ 24 , 25 , 26 ] naphtalimide,[ 27 , 28 , 29 , 30 , 31 ] pyrene[ 32 , 33 , 34 , 35 , 36 ] or oligothiophene (Figure 1 ). [ 37 , 38 ] All of them already successfully demonstrated their ability to increase excited‐state lifetimes and to broaden the absorption profile of the corresponding transition metal complexes.…”

Pyrimidoquinazolinophenanthroline Opens Next Chapter in Design of Bridging Ligands for Artificial Photosynthesis**

“…[(tbbpy) 2 Ru(phenBr 2 )] 2+ ; tbbpy=4,4′‐di‐ tert ‐butyl‐2,2′‐bipyridine; phenBr 2 =5,6‐dibromo‐1,10‐phenanthroline) precursor, followed by a thermal dehydrogenation reaction using palladium on charcoal (Pd/C). This chemistry‐on‐the‐complex approach was selected, as different attempts to synthesise the free pqp ligand (pqp=pyrimido[5′,4′:7,8]quinazolino[5,6‐ f ][1,10]phenanthroline) following previously published procedures failed, [26,27] possibly due to the electron deficient nature of the pyrimidyl groups.…”