Increase In Non-radiative Decay Research Articles

BF2-Oxasmaragdyrin Nanoparticles: A Non-toxic, Photostable, Enhanced Non-radiative Decay-Assisted Efficient Photothermal Cancer Theragnostic Agent.

Photothermal therapy (PTT), a simple and minimally invasive procedure, is an attractive option for cancer therapy. To date, inorganic agents have been widely employed as photothermal agents; however, organic molecules may provide a solution to rapid metabolic/in vivo clearance. Herein, we prepared lipid (S 75)-stabilized meso-tritolyl-BF2-oxasmaragdyrin nanoparticles (TBSNPs) using thin-film hydration and homogenization. Assessment of the physicochemical properties of the TBSNPs reveals the formation of particles of size <12 nm stabilized within the lipid matrix. The TBSNPs exhibit near infrared fluorescence (NIRF) being accompanied by an increase in non-radiative decay, leading to excellent photothermal properties. In vitro studies demonstrate excellent biocompatibility, hemocompatibility, cellular internalization, and photothermal efficacy (p = 0.0004). Extensive in vivo assessment of TBSNPs also highlights the non-toxic nature of the material and passive tumor homing. The strong NIRF exhibited by the material is exploited for whole-body imaging in the rodent model. The novel material also shows excellent photothermal efficacy (p = 0.0002) in a 4T1 xenograft mice model. The organic nature of the material coupled with its small size and strong NIRF provides an advantage for bio-elimination and potential clinical image-guided therapy over the inorganic counterparts.

Sensing Temperature in Vitro and in Cells Using a BODIPY Molecular Probe.

Boron dipyrromethene (BODIPY) molecular rotors have shown sensitivity toward viscosity, polarity, and temperature. Here, we report a 1,3,5,7-tetramethyl-8-phenyl-BODIPY modified with a polyethylene glycol (PEG) chain, for temperature sensing and live cell imaging. This new PEG-BODIPY dye presents an increase in nonradiative decay as temperature increases, which directly influences its lifetime. This change in lifetime is dependent on changes in both temperature and viscosity at low viscosity values, but is only dependent on temperature at high viscosity values. The dependence of fluorescence lifetime with temperature allows for temperature monitoring in vitro and in cells, with sub degree resolution. When in contact with cells, the PEG-BODIPY spontaneously penetrates and stains the cell but not the nucleus. Furthermore, no significant cell toxicity was found even at 100 μM concentration. Using fluorescence lifetime imaging microscopy (FLIM), we were able to observe the changes in the lifetime of PEG-BODIPY within the cell at different temperatures. The use of FLIM and molecular probes such as PEG-BODIPY can provide important information about cellular temperature and heat dissipation upon medically relevant stimuli, such as radiofrequency ablation and photodynamic therapy.

Oxygen and cerium defects mediated changes in structural, optical and photoluminescence properties of Ni substituted CeO2

Local and long-range structural properties, of sol-gel synthesized, Ce1-xNixO2 (0 ≤ x ≤ 0.1) nanopowders have been investigated. Substitution of Ce4+ by comparably smaller Ni2+/Ni3+ ions leads to decrement in lattice parameters. UV–visible spectra reveal decrease of bandgap with increase of disorder upon increasing Ni substitution. The photoluminescence (PL) spectra reveal five major peaks attributed to various defect states. Ni substitution results in the creation of oxygen vacancies (VO) which further leads to conversion of considerable amount of Ce4+ ions to larger size Ce3+. These changes notably, modify the structure of the host lattice. The defects created along with the structural modifications bring, changes in the PL emission. The disorder in the lattice results in increase of non-radiative decay which reduces the PL emission. An increasing VO and Ce3+ concentration at the surface acts as emission quenching centers. Lattice disorder and VO quantities were estimated using X-ray absorption (XAS), UV–vis and Raman spectroscopy.

Temperature Effect on Dual Fluorescence of 2-(2′-Hydroxyphenyl)benzimidazole and Its Nitrogen Substituted Analogues

The effects of temperature on the dual fluorescence of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) and its nitrogen substituted analogues, viz., 2-(2'-hydroxyphenyl)-3H-imidazo[4,5-b]pyridine (HPIP-b) and 2-(2'-hydroxyphenyl)-1H-imidazo[4,5-c]pyridine (HPIP-c), were investigated in solvents of different polarity and hydrogen bonding capability. Absorption, steady-state, and time-resolved emission spectroscopic techniques were employed for the experimental study. Density functional theoretical calculations were performed to find the relative population of the conformers. The calculations predict that, with increase in temperature, the population of trans-enol increases, while that of cis-enol decreases. At all temperatures, the population ratio of cis-enol to trans-enol increases in the order HPIP-c < HPIP-b < HPBI. Except for HPBI in methanol and ethylene glycol, the fluorescence of both emissions decreases with an increase in temperature and is more pronounced in the tautomer band than in the normal band. The data are analyzed using the Arrhenius and van't Hoff equations. The change in the fluorescence with temperature is governed by (i) the change in the relative population of conformers and (ii) the increase in non-radiative decay from the excited states. The increase in non-radiative decay from the normal emission competes with the increase in the relative population of trans-enol with a rise in temperature.

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, previously calculated tight-binding results differ by a factor of 5 with the measured absolute values. Results from pseudopotential calculations agree well with the measured radiative rates. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics

Solvent effect on photophysical properties of a fluorescence probe: BMVC

Fluorescence studies of 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC) in glycerol/water mixtures allow us to elucidate the photophysical behavior of BMVC upon interaction with different DNA structures. The very weak fluorescence emission of BMVC in highly polar solvents of water is attributed to an increase in nonradiative decay due to the intramolecular twist of the vinyl group induced by charge transfer. Increasing the solvent viscosity and rigidity could lead to large changes in the barrier height and substantial effects on relaxation processes, and result in an enhancement of the fluorescence quantum yield. Similarly, different binding interactions of BMVC with various DNA could perturb the frictions of the reorientation of the vinyl group. We suggest that the intramolecular twist of the vinyl group of BMVC is mainly responsible for the distinct fluorescence emissions under different local environments.

Effects of micelles on excited state intramolecular proton transfer activities of 2-hydroxy 1-naphthaldehyde

The effects of ionic and nonionic micelles on the excited state proton transfer processes of 2-hydroxy 1-naphthaldehyde (HNL) have been reported in this Letter. Deprotonation of HNL is considerably retarded in neutral and anionic micelles than that in cationic type as evinced from the increased neutral emission. Increased anion emission of HNL in cationic micelle is more due to the abundance of hydroxyl ions in the environment as well as less nonradiative deactivation. Anion emission is found to decrease in anionic micelle due to less formation of the conformer along with increase in nonradiative decay. The nonradiative processes from neutral to ionic form and ionic to ground state are less affected in neutral micelle as compared to HNL in ionic micelles.

Correlation between Optical Properties and Chain-Length in a Quasi-One-Dimensional Electronic Polymer

We study the molecular weight dependence of the photophysics of a soluble electroluminescent conjugated polymer DOO-PPV in dilute chloroform solution. The absorption and the fluorescence maxima red-shift progressively with increasing weight as the average chain length increases from approximately 9 to 30 monomer units. At the same time, the fluorescence yield of the polymer decreases even though the radiative rate is found to increase. This behavior is caused by a rapid increase in nonradiative decay as the optical gap of the polymer decreases, and we present a quantitative theory that satisfactorily accounts for the dominance of multiphonon relaxation via internal conversion. We also find that the polymer length at which the optical properties saturate is considerably longer than predicted by theoretical calculations of electronic coherence length or by modeling of absorption data using the Strickler-Berg relationship.

The Effect of Intrinsic Rigidity on the Optical Properties of PPV Derivatives

Abstract Light scattering and optical spectroscopy experiments were performed on [2-methoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene](MEH-PPV), poly[2-butoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene](BEH-PPV), and poly[2-dicholestanoxy-p-phenylene-vinylene](BCHA-PPV) in solution with p-xylene to determine the effects of side chain size on the structure and optical properties of PPV. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the PPV backbone and this change in rigidity has dramatic effects on the photoluminescence of PPV. Quantum yield determination relative to Rhodamine 6G shows the luminescence efficiency of the rigid BCHA-PPV is 0.66 ± 0.05 and that the yield decreases to 0.20 ± 0.05 for MEH-PPV, the most coiled derivative. Excitation profiles show an increase in non-radiative decay at high energies when the backbone is more flexible.

A photoluminescence study of poly(phenylene vinylene) derivatives: The effect of intrinsic persistence length

We report the results of light scattering, absorption, excitation, and emission spectroscopy of three polyphenylene vinylene (PPV) derivatives; poly[2-methoxy, 5-(2′-ethyl-hexyloxy-p-phenylene- vinylene] (MEH-PPV), poly[2-butoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV), and poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV) in solution with p-xylene. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the polyphenylene vinylene backbone and that this change in stiffness has dramatic effects on the photoluminescence of polyphenylene vinylene. We have determined the luminescence quantum efficiencies of the polyphenylene vinylene derivatives relative to a known standard, Rhodamine 6G, and find that the photoluminescence can be greatly enhanced by increasing the intrinsic stiffness of the polymer backbone. The stiffest polymer, poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV), has a quantum efficiency of 0.66±0.05. The quantum efficiency decreases to 0.22±0.05 for poly[2-butoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV) and 0.20±0.05 for poly[2-methoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (MEH-PPV), the most coiled derivative. Excitation profiles of the three derivatives also show an increase in nonradiative decay at high energies when the polymer assumes a more coiled comformation. Thus, the quantum yields are dependent on pump energy.