Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

Charging and ultralong phosphorescence of lanthanide facilitated organic complex

Emission from the triplet state of an organo-lanthanide complex is observed only when the energy transfer to the lanthanide ion is absent. The triplet state lifetime under cryogenic conditions for organo-lanthanide compounds usually ranges up to tens of milliseconds. The compound LaL1(TTA)3 reported herein exhibits 77 K phosphorescence observable by the naked eye for up to 30 s. Optical spectroscopy, density functional theory (DFT) and time-dependent DFT techniques have been applied to investigate the photophysical processes of this compound. In particular, on-off continuous irradiation cycles reveal a charging behaviour of the emission which is associated with triplet-triplet absorption because it shows a shorter rise lifetime than the corresponding decay lifetime and it varies with illumination intensity. The discovery of the behaviour of this compound provides insight into important photophysical processes of the triplet state of organo-lanthanide systems and may open new fields of application such as data encryption, anti-counterfeiting and temperature switching.

I-V Curves of an Apigenin Dye and Their Analysis by a New Parabolic Function

A new parabolic function for I-V curves’ analysis has been proposed. The new “analytical tool” provides a simple way to describe photophysical processes at an approximately monolayer surface of a dye-sensitized solar cell. It may now be possible to estimate factors such as hole–electron recombination, surface defects, and electron diffusion at the semiconductor layer. The theoretical approach that was previously reported by our group for predicting the photovoltaic performance of potential dye sensitizers has also been validated. The experimental photovoltaic and DFT/TD-DFT data of apigenin and those of the highly rated black dyes were used for the validation.

Insights on the impact of photophysical processes and defect states evolution on the emission properties of surface-modified ZnO nanoplates for application in photocatalysis and hybrid LEDs

The effects of surface modification on the defect state densities, optical properties, photocatalytic and quantum efficiencies of zinc oxide (ZnO) nanoplates have been studied in this work. Here, the aim...

Electron spin dynamics in excited state photochemistry: recent development in the study of the intersystem crossing and charge transfer in organic compounds

Electron spin dynamics are crucial to photochemical and photophysical processes. However, to large extent it is neglected in routine photochemistry studies. Herein we summarized the recent development of the electron...