| Ru(Ⅱ) polypyridine complexes are fascinating phosphorescent dyes, which have been extensively used for photovoltaics, biological molecular sensors, luminescence oxygen sensors etc. Phosphorescent dyes with long luminescence lifetimes are ideal for its application, such as oxygen sensors and the energy transfer efficiency of triplet states, etc. Therefore, it has been an important research subject to extend the excited states lifetimes of the phosphorescent complexes. The photophysics of phosphorescent complexes are closely related to the electronic structure of their excited states. Herein, we used DFT/TDDFT theoretical calculation on the rational design of novel Ru(Ⅱ) complexes and for study of their photophysical properties. This complementary experimental and theoretical approach will be helpful in the rational design of new phosphorescent material.Recently we and others found that the excited states of the Ru(II) complexes can be tuned by ligand modification. We observed exceptionally long luminescence lifetime (τ= 108.0μs) of pyrenylethynylene containing complex Ru-4, the T1 state lifetime was prolonged by 240-fold compared to 0.45μs for the parent complex Ru-1. The DFT/TDDFT calculations support the postulation that the emission of the complex Ru-4 is due to the ligand centered triplet state (3IL), rather than the traditional 3MLCT state. The effects of the lifetime extension on the oxygen sensing properties of these complexes were studied in both solution and polymer films. With tuning the emissive states, and thus extension of the luminescence lifetimes, the luminescent O2 sensing sensitivity of the complexes Ru-4 can be improved by ca.150-fold than complex Ru-1.The Ru(II) complexes with rigid imidazole ligands were studied. The excited states of this kind of Ru(II) complexes can also be tuned by introducing right chromophores. For the 3MLCT and 3IL states, the energy level of Ru(II) complexes with anthracene is non-eqiilibrium states. The non-conjugation between anthracene and imidazole hindered the anergy transfer from 3MLCT state to 3IL. The emission mechanism was studied with transient absorption, excited state lifetime, emission at room temperature and 77 K, theoretical calculations, et al.Photon upconversion, the process wherein light of lower energy is converted to photons of higher energy, is readily achieved at low incident power through sensitized triplet-triplet annihilation (TTA), which is important for photovoltaics etc. Herein it is for the first time that the effect of the excited-state lifetimes of sensitizers on the TTA upconversion (UC) efficiency was investigated with the Ru(Ⅱ) or Pt(Ⅱ) complexes as sensitizers and DPA as acceptor. Our results demonstrated that the 3IL excited state with longer excited state lifetime is much more efficient in sensitizing the TTA-based upconversion than the 3MLCT excited states. We also found that UC efficiency could be affected by the energy gap between sensitizers’ excited states and the 3π-π* state of DPA.In this paper the long-lived 3IL excited state of Ru-4 (τ=108.0μs) was used as triplet sensitizer for TTA, but only moderate upconversion quantum yield (9.8%) were observed which is about 10 times higher than that of Ru-1 (ΦUC=0.9%), for which the excited state is the normal 3MLCT state (τ=0.45μs). In order to tackle the drawback, we propose Pt-3 as sensitizer with long lifetime 3IL (τ=108.0μs) and an astonishing upconversion quantum yield of 39.9% was observed, which exceed the previously predicted maximal TTA upconversion quantum yields (11.1%). For Pt-3, the TTET driving force (the energy gap between the triplet excited state of the sensitizer and acceptorΔET-T=1638 cm-1) is larger than that of Ru-4 (ΔET-T=707 cm-1). Our results raised a question that re-consideration of the photophysical process of TTA upconversion, both theoretically and experimentally.It is for the first time that non-phosphorescent transition metal complexes with triplet excited state populated upon photo-excitation is proposed to be able to sensitize the TTA UC. Our result will greatly increase the availability of the triplet sensitizers for triplet-triplet-annihilation based upconversion.We carried out DFT/TDDFT theoretical calculation to investigate the sensing mechanism of luminophores protected by 2,4-dinitrobenzenesulfonyl, and we propose that the non-luminescence feature is due to the dark excited state induced by the DNBS moiety, not the collapse of the D-π-A character of the luminophores suggested in literature. Our results infer the modular luminophores unit that can be used for this kind of thiol probes is more abundant than previously thought. We designed a highly selective OFF-ON thiol probe based on this sensing mechanism by using Ru(Ⅱ) poly(1,10-phenanthroline) complex as the luminophores. The probe was successfully used for bioimaging of thiols in living cells, which will be helpful in the medical diagnostic process. |
PDF Full Text Request