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Neutral heteroleptic cyclometallated Platinum(II) complexes featuring 2-phenylbenzimidazole ligand as bright emitters in solid state and in solution
摘要： A series of 8 neutral cyclometallated platinum(II) complexes featuring 2-phenylbenzimidazole chromophoric ligand and acetylacetonate as ancillary ligand has been synthesized and characterized. The introduction of a variety of substituent on the phenyl ring allows to finely tune the emission wavelength. The emission data reveal high quantum yield in deaerated solution and in bulk solid state (micro-crystalline powder), with values up to an impressive 51%. The emission for all of the complexes is attributed to a mixed 3LC-MLCT state. Both absorption and emission data have been correlated successfully with the redox potentials and the Hammett parameters.
关键词： photophysics,phosphorescence,platinum,organometallic,solid state emission
更新于2025-09-10 09:29:36
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Resonance Energy Transfer in a Genetically Engineered Polypeptide Results in Unanticipated Fluorescence Intensity
摘要： The fluorescence intensity of a C-terminal acceptor chromophore, N-(7-dimethylamino-4-methyl coumarin (DACM), increased proportionally with 280 nm irradiation of an increasing number of donor tryptophan residues located on a β-sheet forming polypeptide. The intensity of the acceptor chromophore increased even as the length of the β-sheet edge approached 256 ?, well beyond the F?rster radius for the tryptophan-acceptor chromophore pair. The folding of the peptides under investigation was verified by circular dichroism (CD) and deep UV resonance Raman experiments. Control experiments showed that fluorescence occurred concomitantly with peptide folding. In other control experiments, the DACM fluorescence intensity of the solutions of tryptophan and DACM did not show any enhancement of DACM fluorescence with increasing tryptophan concentrations. Formation of fibrillar aggregates of the substrate peptides prepared for the fluorescence studies was undetectable by thioflavin T(ThT) fluorescence.
关键词： fluorescence,energy transfer,protein folding,photophysics,peptides
更新于2025-09-10 09:29:36
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Photophysical and photocatalytic properties of corrophyll and chlorophyll
摘要： Tetrapyrrolic macrocycles are well known photosensitizers, absorbing light in the ultraviolet and visible region. The quantum e?ciency of these naturally occurring compounds in optical processes, and the possibility of altering their behavior by modifying its constituent features, make them promising candidates for applications as Dye Sensitized Solar Cells (DSSC) and photocatalytic reactions. The time-dependent density-functional theory (TD-DFT) were used to study the optical and redox properties of chlorophyll and corrin-related molecules (corrophyll). The in?uence of the substituents and metallic atoms in their properties have been investigated. Our results show lower reduction potentials for corrophyll molecules compared with chlorophyll. The optical absorbance spectra of corrophyll without a metallic atom at their central rings shows a signi?cant blue-shift, as compared to their chlorophyll counterparts. The presence of Co(I) ion species at the corrophyll core leads to oxidation potentials below than that of water, which puts corrophyll ahead of traditional chlorophyll pigments as photocatalysts. We show that the substituents and the ions coordinated to the macrocycles play an important role in this phenomena. These ?ndings show the great potential of tuning the spectroscopic and reactive properties of tetrapyrrole macrocycles for applications in photocatalysis and optoelectronic devices, while keeping their essential structural features intact.
关键词： Corrole,Photophysics,Porphyrin,Electronic structure,TD-DFT,Optical absorbance,Photocatalysis
更新于2025-09-10 09:29:36
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Synthesis, characterization and optical properties of novel Ir(III) complexes bearing N-heterocycle substituents
摘要： A series of cationic heteroleptic Ir(III) complexes with different N-heterocycle groups (N-phenothiazinyl, N-indolyl, N-carbazolyl, 3,6-di-tert-butyl-N-carbazolyl) were synthesized and characterized. The photophysical properties of these complexes were systematically investigated. All complexes exhibit strong 1π-π* absorption bands in the UV region and broad 1MLCT absorption bands in the visible region. In addition, these complexes exhibit weak absorption after 500 nm, which could be attributed to 3π,π*/3CT transition. All complexes exhibit broad and structureless emission bands from 568 nm to 627 nm at room temperature, which are originated from 3MLCT/3LLCT excited states. The electron donating substituents attached on the 2-phenylpyridine ligands cause a pronounced red-shift of the emission band. Except 1d, all complexes show strong triplet transient absorptions from UV to visible region, which were assigned to the 3MLCT/3π,π* excited state. In addition, complexes 1a-1c all exhibit reverse saturable absorption (RSA) at 532 nm, which follows the trend of 1a>1b>1c. The photophysical properties of these Ir(III) complexes can be influenced drastically by the substituents on 2-phenylpyridine ligands, which would be useful for rational design of optical functional materials.
关键词： Nonlinear absorption,Synthesis,N-heterocycle,Photophysics property,Ir(III) complex
更新于2025-09-09 09:28:46
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Photophysics at Unusually High Dye Concentrations
摘要： The study of the interaction of light with systems at high dye concentrations implies a great challenge because several factors, such as emission reabsorption, dye aggregation, and energy trapping, hinder rationalization and interpretation of the involved photophysical processes. Space constraints induce dye interaction even in the absence of ground state stabilization of dimers and oligomers. At distances on the order of 1 nm, statistical energy traps are usually observed. At longer distances, excited state energy transfer takes place. Most of these factors do not result in ground state spectroscopic changes. Rather, fluorescence phenomena such as inner filter effects, concentration-dependent Stokes’ shifts, and changes in quantum yields and decay times are evidenced. Photophysical studies are commonly carried out at high dilution, to minimize dye?dye interactions and emission reabsorption, and in the absence of light scattering. Under these conditions, the system becomes rather simple. Fluorescence and triplet quantum yields become molecular properties and can be easily related to ratios of rate constants. However, many systems containing dyes able to fulfill specific functions, whether man-made or biological, are far from being dilute and scattering-free. The photosynthetic apparatus is a paradigmatic example. It is clear that isolation of components allows gathering relevant information about complex systems. However, knowledge of the photophysical behavior in the unaltered environment is essential in most cases. Complexity generally increases when light scattering is present. Despite that, our experience shows that light scattering, when correctly handled, may even simplify the task of unraveling molecular parameters. We show that methods and models aiming at the determination and interpretation of fluorescence and triplet quantum yields as well as energy transfer efficiencies can be developed on the basis of simple light-scattering theories. Photophysical studies were extended to thin films and layer-by-layer assemblies. Procedures are presented for the evaluation of fluorescence reabsorption in concentrated fluid solutions up to the molar level, which are being applied to ionic liquids, in which the emitting species are the bulk ions. Fluorescence reabsorption models proved to be useful in the interpretation of the photophysics of living organisms such as plant leaves and fruits. These new tools allowed the assessment of chlorophyll fluorescence at the chloroplast, leaf and canopy levels, with implications in remote sensing and the development of nondestructive optical methods.
关键词： light scattering,dye concentrations,photophysics,fluorescence reabsorption,energy transfer
更新于2025-09-09 09:28:46
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Intrinsic and Extrinsic Heavy Atom Effect on the Multifaceted Emissive Behavior of Cyclic Triimidazole
摘要： Since heavy halogen atoms can be used to tune the emissive properties of organic luminogens, the understanding of their role in the photophysics is fundamental for materials engineering. Here, the extrinsic and intrinsic heavy atom effects on the photophysics of organic crystals are separately evaluated by comparing cyclic triimidazole (TT) with its mono-iodo derivative (TTI) and its cocrystal with diiodotetrafluorobenzene (TTCo). Crystals of TT show room temperature ultralong phosphorescence (RTUP) originated from H-aggregation. TTI and TTCo display two additional long lived components whose origin is elucidated through single crystal X-ray and DFT-TDDFT studies. The results highlight the different effects of the I atom on the three phosphorescent emissions. Intrinsic heavy atom effects play a major role on molecular phosphorescence which is displayed at RT only for TTI. H-aggregate RTUP and the I···N XB induced phosphorescences on the other side depend only on packing features.
关键词： photophysics,co-crystal,room temperature phosphorescence,halogen bonding,time resolved spectroscopy
更新于2025-09-04 15:30:14
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Atomic structure of a fluorescent Ag <sub/>8</sub> cluster templated by a multi-stranded DNA scaffold
摘要： Multinuclear silver clusters encapsulated by DNA exhibit size-tunable emission spectra and rich photophysics, but their atomic organization is poorly understood. Herein, we describe the structure of one such hybrid chromophore, a green-emitting Ag8 cluster arranged in a Big Dipper shape bound to the oligonucleotide A2C4. Three 3’ cytosine metallo-base pairs stabilize a parallel A-form-like duplex with a 5’ adenine-rich pocket, which binds a metallic, trapezoidal-shaped Ag5 moiety via Ag-N bonds to endo- and exo-cyclic nitrogens of cytosine and adenine. The unique DNA configuration, constrained coordination environment, and templated Ag8 cluster arrangement highlight the reciprocity between the silvers and DNA in adopting this structure. These first atomic details of a DNA-encapsulated Ag cluster fluorophore illuminate many aspects of biological assembly, nanoscience, and medical imaging.
关键词： crystallography,photophysics,silver,crystals,DNA,materials,nanocluster,nanomaterials,emissive cluster
更新于2025-09-04 15:30:14
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Effects of Varying the Benzannulation Site and π Conjugation of the Cyclometalating Ligand on the Photophysics and Reverse Saturable Absorption of Monocationic Iridium(III) Complexes
摘要： A series of monocationic iridium(III) complexes, [Ir(C^N)2(pqu)]+PF6? [pqu = 2-(pyridin-2-yl)quinoline, C^N = 2-phenylquinoline (1), 3-phenylisoquinoline (2), 1-phenylisoquinoline (3), benzo[h]quinoline (4), 2-(pyridin-2-yl)naphthalene (5), 1-(pyridin-2-yl)naphthalene (6), 2-(phenanthren-9-yl)pyridine (7), 2-phenylbenzo[g]quinoline (8), 2-(naphthalen-2-yl)quinoline (9), and 2-(naphthalen-2-yl)benzo[g]quinoline (10)], were synthesized in this work. These complexes bear C^N ligands with varied degrees of π conjugation and sites of benzannulation, allowing for elucidation of the effects of the benzannulation site at the C^N ligand on the photophysics of the complexes. Ultraviolet?visible (UV?vis) absorption and emission of the complexes were systematically investigated via spectroscopic techniques and time-dependent density functional theory calculations. Their triplet excited-state absorption and reverse saturable absorption (RSA) were studied by nanosecond transient absorption (TA) spectroscopy and nonlinear transmission techniques. The fusion of phenyl ring(s) to the phenyl ring or the 4 and 5 positions of the pyridyl ring of the C^N ligand resulted in red-shifted UV?vis absorption and emission spectra in complexes 2, 5?7, 9, and 10 compared to those of the parent complex 0, while their triplet lifetimes and emission quantum yields were significantly reduced. In contrast, the fusion of one phenyl ring to the other sites of the pyridyl group of the C^N ligand showed an insignificant impact on the energies of the lowest singlet (S1) and triplet (T1) excited states in complexes 1, 3, and 4 but noticeably affected their TA spectral features. The fusion of the naphthyl group to the 5 and 6 and positions at the pyridyl ring did not influence the S1 energy of complex 8 but altered the nature of the T1 states in 8 and 10 by switching them to the benzo[g]quinoline-localized 3π,π* state, which resulted in completely different emission and TA spectra in these two complexes. The site-dependent variations of the ground- and excited-state absorption induced strong but varied RSA from these complexes for 4.1-ns laser pulses at 532 nm, with the RSA strength decreasing in the trend of 3 > 7 ≈ 4 ≈ 9 ≈ 6 > 8 ≈ 1 ≈ 2 ≈ 5 > 10.
关键词： iridium(III) complexes,time-dependent density functional theory,spectroscopic techniques,photophysics,reverse saturable absorption,benzannulation
更新于2025-09-04 15:30:14
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Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response
摘要： Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable ?uorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many ?elds, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the ?eld of CDs, with a focus on the fundamental understanding of their key photophysical behaviour, which is still very debated. The photoluminescence mechanism, the origin of their peculiar ?uorescence tunability, and their photo-chemical interactions with coupled systems are discussed in light of the latest developments in the ?eld, such as the most recent results obtained by femtosecond time-resolved experiments, which have led to important steps forward in the fundamental understanding of CDs. The optical response of CDs appears to stem from a very complex interplay between the electronic states related to the core structure and those introduced by surface functionalization. In addition, the structure of CD energy levels and the electronic dynamics triggered by photo-excitation ?nely depend on the microscopic structure of any speci?c sub-type of CD. On the other hand, this remarkable variability makes CDs extremely versatile, a key bene?t in view of their very wide range of applications.
关键词： femtosecond,photophysics,ultrafast,carbon dots,nanocarbon,photochemistry,fluorescence
更新于2025-09-04 15:30:14