Zhongjing Li

Nonlinear Absorbing Platinum(II) Diimine Complexes: Synthesis, Photophysics, and Reverse Saturable Absorption

A series of platinum(II) diimine complexes with different substituents on fluorenyl acetylide ligands (1a-1e) were synthesized and characterized. The influence of the auxiliary substituent on the photophysics of these complexes has been systematically investigated spectroscopically and theoretically (using density functional theory (DFT) methods). All complexes exhibit ligand-centered (1)π,π* transitions in the UV and blue spectral region, and broad, structureless (1)MLCT/(1)LLCT (1a, 1b, 1d and 1e) or (1)MLCT/(1)LLCT/(1)π,π* (1c) absorption bands in the visible region. All complexes are emissive in solution at room temperature, with the emitting state is tentatively assigned to mixed (3)MLCT/(3)π,π* states. The degree of (3)π,π* and (3)MLCT mixing varies with different substituents and solvent polarities. Complexes 1a-1e exhibit relatively strong singlet and triplet transient absorption from 450 to 800 nm, at which point reverse saturable absorption (RSA) could occur. Nonlinear transmission experiments at 532 nm by using nanosecond laser pulses demonstrate that 1a-1e are strong reverse saturable absorbers and could potentially be used as broadband nonlinear absorbing materials.

Tuning Photophysics And Nonlinear Absorption Of Bipyridyl Platinum(ii) Bisstilbenylacetylide Complexes By Auxiliary Substituents

The photophysics of six bipyridyl platinum(II) bisstilbenylacetylide complexes with different auxiliary substituents are reported. These photophysical properties have been investigated in detail by UV-vis, photoluminescence (both at room temperature and at 77 K) and transient absorption (nanosecond and femtosecond) spectroscopies, as well as by linear response time-dependent density functional theory (TD-DFT) calculations. The photophysics of the complexes are found to be dominated by the singlet and triplet π,π* transitions localized at the stilbenylacetylide ligands with strong admixture of the metal-to-ligand (MLCT) and ligand-to-ligand (LLCT) charge-transfer characters. The interplay between the π,π* and MLCT/LLCT states depends on the electron-withdrawing or -donating properties of the substituents on the stilbenylacetylide ligands. All complexes exhibit remarkable reverse saturable absorption (RSA) at 532 nm for nanosecond laser pulses, with the complex that contains the NPh(2) substituent giving the strongest RSA and the complex with NO(2) substituent showing the weakest RSA.

Synthesis, photophysics, and reverse saturable absorption of 7-(benzothiazol-2-yl)-9,9-di(2-ethylhexyl)-9H-fluoren-2-yl tethered [Ir(bpy)(ppy)2]PF6 and Ir(ppy)3 complexes (bpy = 2,2′-bipyridine, ppy = 2-phenylpyridine)

We report the synthesis, photophysics, and reverse saturable absorption of five iridium(III) complexes 1–5 with 7-(benzothiazol-2-yl)-9,9-di(2-ethylhexyl)-9H-fluoren-2-yl (BTF) pendant attached to the 2-phenylpyridine ligand (1: [Ir(bpy)(BTF-ppy)2]PF6; 2: [Ir(bpy)(BTF––ppy)2]PF6; 3: Ir(ppy)2(BTF-ppy); 4: Ir(ppy)(BTF-ppy)2; 5: (BTF-ppy)3, where bpy = 2,2′-bipyridine and ppy = 2-phenylpyridine). The effects of the extended π-conjugation of the ppy ligand and the increased number of BTF-ppy ligand, as well as the effects of neutral complex vs. cationic complex were evaluated. All complexes exhibit predominantly ligand-localized 1π,π* transitions below 430 nm and charge-transfer transitions between 430 and 550 nm. They all emit at room temperature and at 77 K, mainly from the metal-to-ligand charge transfer (3MLCT)/ligand-to-ligand charge transfer (3LLCT) states for 1 and 2, and from the BTF-ppy ligand-centered 3π,π* excited states with significant contributions from the 3MLCT states for 3–5. The triplet excited states of 1–5 also manifest broad transient absorption (TA) in the visible to the near-IR spectral region. The electronic absorption, emission, and ns transient absorption are all red-shifted by extending the π-conjugation of the ppy ligand or increasing the number of BTF-ppy ligand. The energies of the lowest singlet and triplet excited states of the neutral complex 4 are lowered compared to those of its cationic counterpart 1; while the transient absorbing triplet excited state of 4 is much longer lived than that of 1. These complexes all exhibit strong reverse saturable absorption (RSA) for ns laser pulses at 532 nm, with a trend of 5 < 4 < 1 ≈ 3 < 2. This trend is primarily determined by the ratio of the excited-state absorption cross section to that of the ground state (σex/σ0) at 532 nm with the triplet quantum yield also playing a role for complexes 3–5. It appears that the increased number of BTF-ppy ligand reduces the RSA of the neutral complexes while the increased π-conjugation of the ppy ligand in the cationic complexes improves the RSA. However, the neutral complex 4 exhibits a weaker RSA at 532 nm than its cationic counterpart 1.

Strong triplet excited-state absorption in a phenanthrolinyl iridium(III) complex with benzothiazolylfluorenyl-substituted ligands

Femtosecond transient difference absorption (fs TA) measurements, together with a series of open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies, were performed on a 1,10-phenanthrolinyl iridium(III) complex bearing ligands containing a benzothiazolylfluorenyl motif. An analysis of decay data from the fs TA experiment yields a value of 1.24±0.26  ns for the singlet excited-state lifetime τ(S) of the complex. By fitting the Z scans to a five-level dynamic model incorporating the independently measured value of τ(S) and previously reported values of the complexs triplet quantum yield (0.13) and triplet excited-state lifetime (230 ns), we obtain values of 3.5×10(-17)  cm(2) (singlet) and 5.0×10(-16)  cm(2) (triplet) for the excited-state absorption cross-sections of the complex in toluene solution at 532 nm; the latter value represents one of the largest triplet excited-state absorption cross-sections ever reported at this wavelength. The ratio of the triplet excited-state cross-section to the ground-state absorption cross-section exceeds 3800.

Polyphosphazenes with Immobilized Dyes as Potential Color Filter Materials.

Red, green, and blue dye molecules were linked covalently to polyphosphazenes to generate soluble, film-forming materials appropriate for the formation of patterned tricolor filters for possible use in liquid crystalline and other display devices or in camera sensors. The monofunctional dyes (a red 1-[(E)-(4-nitrophenyl)diazenyl]-2-naphthol, a green tetraphenylporphyrin [5-(4-hydroxyphenyl)-10,15,20-tetraphenylporphyrin], and a toluidine blue dye) were employed as representative chromophores. The cosubstituents employed included 2,2,2-trifluoroethoxy with and without aryloxy groups or cyclopentanoxy groups. The optical densities were varied by adopting several dye-to-cosubstituent side group ratios. These dyes are models for a wide range of different chromophores that can be linked to polyphosphazene chains.

A new textured polyphosphazene biomaterial with improved blood coagulation and microbial infection responses

A new poly[bis(octafluoropentoxy) phosphazene] (OFP) was synthesized for the purpose of blood contacting medical devices. OFP was further either developed into crosslinkable polyphosphazene (X-OFP) or blended with polyurethane (PU) as the mixture (OFP/PU) for improvement of mechanical property of polyphosphazene polymers. All the materials were fabricated as smooth films or further textured with submicron pillars for the assay of antimicrobial and antithrombotic properties. Results showed that crosslinkable OFP (X-OFP) and blends of OFP/PU successfully improved the mechanical strength of OFP and fewer defects of pillars were found on the textured polyphosphazene surfaces. The antithrombotic experiments showed that polyphosphazene OFP materials reduced human Factor XII activation and platelet adhesion, thereby being resistant to plasma coagulation and thrombosis. The bacterial adhesion and biofilm experiments demonstrated that OFP materials inhibited staphylococcal bacterial adhesion and biofilm formation. The surface texturing further reduced the platelet adhesion and bacterial adhesion, and inhibited biofilm formation up to 23 days. The data suggested that textured OFP materials may provide a practical approach to improve the biocompatibility of current biomaterials in the application of blood contacting medical devices with significant reduction in risk of pathogenic infection and thrombosis. STATEMENT OF SIGNIFICANCE The thromboembolic events and microbial infection have been the significant barriers for the long term use of biomaterials in blood-contacting medical devices. The development of new materials with multiple functions including anti-thrombosis and antibacterial surfaces is a high research priority. This study synthesized new biostable and biocompatible polyphosphazene polymers, poly[bis(octafluoropentoxy)phosphazene] (OFP) and crosslinkable OFP, and successfully improved the mechanical strength of polyphosphazenes. Polymers were fabricated into textured films with submicron pillars on the surfaces. The antimicrobial and antithrombotic assays demonstrated that new materials combined with surface physical modification have significant reduction in risk of pathogenic infection and thrombosis, and improve the biocompatibility of current biomaterials in the application of blood-contacting medical devices. It would be interest to biomaterials and bioengineering related communities.

Synthesis and photophysics of a broadband absorbing texaphyrin derivative bearing a Rhodamine 6G motif

A texaphyrin derivative with Rhodamine 6G attached (complex 11) via a CC bond was synthesized and characterized. The UV-vis absorption, emission and nanosecond transient absorption (TA) characteristics of this complex were systematically studied in acetone solutions. The photophysics of this complex was also compared with those of its precursor compounds texaphyrins 12 and 13 and the Rhodamine 6G derivative 3. The UV-vis absorption spectrum of 11 consists of both the characteristic Soret and Q bands of the texaphyrin derivative 13 and the identical absorption band from the Rhodamine 6G derivative 3. When excited at 550 nm (the major absorption band of Rhodamine 6G), 11 exhibits fluorescence bands from both the Rhodamine 6G component (582 nm) and texaphyrin component (802 nm), but the intensity of the 582 nm band dramatically reduced accompanied by a significant increase of the 802 nm band compared to those from 3 and 13, indicating electron/energy transfer from the singlet excited state of Rhodamine 6G. The ns TA spectrum of 11 resembles that of the texaphyrin derivative 13 but with both the bleaching band and absorption band red-shifted. The triplet lifetimes deduced from the decay of ns TA are quite similar for 11, 12 and 13, indicating the lack of interactions between the triplet excited states of the texaphyrin component and the Rhodamine 6G component. The broadband ground-state absorption of 11 from the visible to the near-IR region, and the possible electron/energy transfer from the singlet excited state of the Rhodamine 6G component to the texaphyrin component suggest that this complex could potentially be a broadband photosensitizer for dye-sensitized solar cell applications.