Environmental effects on the photophysics of transition metal complexes with dipyrido[2,3-a:3′,2′-c]phenazine (dppz) and related ligands

Pushing the limit: synthesis, photophysical and DNA binding studies of a NIR-emitting Ru(ii)-polypyridyl probe with ‘light switch’ behaviour

“…Inspired by the work of Meyer et al and Zhou et al who have recently developed a number of Ru(II)-polypyridyl complexes which exhibit 1 MLCT absorbance maxima as long as 550 nm and a singlet oxygen quantum yield as high as 0.43, 12 we set out to develop 1 based on 2, a new polypyridyl ligand, which we have named 'DipyTAP' as it contains two well established polypyridyl ligands within a single structure. We foresaw that through the use of a delocalized π-system the 1 MLCT absorption of 1 may be shifted to longer wavelengths as has been reported by Zhou et 2+ and related structures, 13,14 but upon interaction of 1 with DNA the quenching process is perturbed resulting in an increase in the observed luminescence. To the best of our knowledge this is the first example of a Ru(II)-polypyridyl complex that can both act as a light switch for DNA, absorbing between 500 and 600 nm; emitting at long wavelengths within the NIR region, with an emission window between 700 and 850 nm; of significant importance, particularly for applications in imaging and photo-therapy.…”

Preferred orientation in an angled intercalation site of a chloro-substituted Λ -[Ru(TAP) 2 (dppz)] 2+ complex bound to d(TCGGCGCCGA) 2

“…After washing with a small quantity of ethanol, the product was dried under vacuum, extracted into water : ethanol 1 : 1 (5 ml; using ultrasound and gentle heating to effect solution), filtered hot and the residue dried under vacuum (78.7 mg). 1 (c) Crystallization, data collection, structure solution and refinement…”

“…We suggest that this might be due to the 'anchoring' effect of the semi-intercalation by TAP1, which leads to unresolved minor differences in the orientations of TAP2 that could be correlated with the two orientations of the asymmetrically substituted dppz ( figure 3). The unsubstituted complex ions [Ru(phen) 2 dppz] 2+ and [Ru(TAP) 2 dppz] 2+ show luminescence (specifically ML(phen)CT and ML(TAP)CT) when intercalated into DNA, and there has been much literature discussion about the factors required for a long luminescent lifetime [1]. The best studied system, [Ru(phen) 2 dppz] 2+ , has phenanthroline groups as ancillary ligands on the ruthenium, in which case no luminescence was observed in aqueous solution [1].…”

“…The unsubstituted complex ions [Ru(phen) 2 dppz] 2+ and [Ru(TAP) 2 dppz] 2+ show luminescence (specifically ML(phen)CT and ML(TAP)CT) when intercalated into DNA, and there has been much literature discussion about the factors required for a long luminescent lifetime [1]. The best studied system, [Ru(phen) 2 dppz] 2+ , has phenanthroline groups as ancillary ligands on the ruthenium, in which case no luminescence was observed in aqueous solution [1]. It is widely assumed that the intense luminescence when intercalated into DNA is due to the exclusion of water from the pyrazine N of the dppz ligand.…”

“…The photophysical behaviour has been comprehensively reviewed [1], but much less is known about the precise DNA binding modes of this family of complexes. The 'light-switch' complexes such as [Ru(phen) 2 [Ru(bpy) 2 (dppz)] 2+ have been particularly intensively studied in solution and were finally shown to crystallize with DNA decamer duplexes [2,3].…”