Role of diffusion in excitation energy transfer and migration

Förster Resonance Energy Transfer between Fluorescent Organic Semiconductors: Poly(9,9-dioctylfluorene-alt-benzothiadiazole) and 6,13-Bis(triisopropylsilylethynyl)pentacene

In the present study, an investigation of the electronic excitation energy transfer between two p-type fluorescent semiconductors, F8BT [poly(9,9-dioctylfluorene-alcohol-benzothiadiazole] and TIPS-P [6,13-bis(triisopropylsilylethynyl)pentacene], has been carried out in a chloroform solution using steady-state and time-domain fluorescence techniques. The spectral overlap integral between donor (F8BT) emission and acceptor (TIPS-P) absorption is 2.04 × 10¹⁵ nm⁴/(M cm), and the corresponding critical transfer distance is 53.12 Å. In donor decay dynamics, at the lower acceptor concentrations, the observed results deviate from the Förster theory due to the combined effect of diffusion and energy migration. However, it does not exhibit energy migration and distribution for higher acceptor concentrations, and the system follows the Förster model of resonance excitation energy transfer (FRET). The higher value of the donor-acceptor interaction strength than self-interaction (donor-donor interaction) appears to be responsible for this behavior. Further, in acceptor decay, the appearance of the rise time and its decrease with the acceptor concentration confirms FRET from F8BT to TIPS-P.

A simulation study on the influence of energy migration and relative interaction strengths of homo- and hetero-FRET on the net FRET efficiency

Förster resonance energy transfer (FRET) is a powerful method for probing biomolecular conformations and dynamics in bulk as well as at a single-molecule level. FRET utilizes non-radiative mechanisms to transfer energy between fluorophores, donor and acceptor when placed in close proximity. The FRET efficiency has a strong distance dependence and serves as a direct read-out for molecular interaction. In case of a significant overlap of donor emission and absorption spectra, the excited state energy can be exchanged between the identical donors in close proximity, which eventually migrates back and forth until it gets dissipated. This form of energy transfer is called energy migration or homo-FRET. Here, we have simulated FRET efficiency by considering the donor-donor interaction strength (ξ_DD) and donor-acceptor interaction strength (ξ_DA) under conditions of non-uniform distribution of molecules. Our earlier studies indicate that energy migration modulate the FRET efficiency for various values of ξ_DD and ξ_DA. We, therefore, determined the limiting values of acceptor concentration (C_LA) that will allow the determination of FRET efficiency in the absence and presence of energy migration. Taken together, our study optimizes the conditions for meaningful FRET efficiency for a given FRET pair for better reporting of molecular interactions.

Comment on the article "Investigation of Fluorescence Resonance Energy Transfer between Fluorescein and Rhodamine 6G"

In this comment we, report the missing of relevant literature regarding Forster energy transfer (FRET) between fluorescein and rhodamine 6G in a recent paper (Spectrochim. Acta A, 149 (2015) 143-149). In this paper, the authors claim that "a new FRET pair" has been identified, which is absolutely incorrect. In fact, studies on FRET in this dye pair under different conditions have been done earlier. Further, the estimated critical transfer distance may have uncertainty because of donor quantum yield which is not clarified in the paper.

Effect of diffusion on Förster resonance energy transfer in low-viscosity solution

The effect of translational diffusion on Förster resonance energy transfer between rhodamine 6G (the donor) and malachite green (the acceptor) was investigated by examining the donor's fluorescence decay profile. Eight straight-chain alkyl alcohols were used, and the temperature of ethanol was changed to vary the viscosity; the decay profiles were analyzed using the theory developed by Gösele. The critical transfer distance obtained from the decay profile is in good agreement with that evaluated using the spectroscopic quantities, and the diffusion coefficients are consistent with the Stokes-Einstein relation. The fluorescence decay profile was described well by Gösele's theory and the effect of diffusion is clearly verified by the temperature/viscosity dependence of the diffusion constant.

Unusual photoluminescence properties of the 3D mixed-lanthanide–organic frameworks induced by dimeric structures: a theoretical and experimental approach

Experimental and theoretical investigation of the 3D Ln-MOFs that present singular spectral signature.

Long-distance fluorescence lifetime imaging using stimulated emission

Long-distance stimulated emission imaging has recently been demonstrated as a novel approach for the characterization and imaging of samples containing fluorescent moieties. We present an extension of this methodology through a pump-probe setup for fluorescence lifetime determination and imaging. We measure fluorescence lifetimes of Rhodamine 6G at different solutions and indocyanine green using long-distance fluorescence lifetime imaging.

Photoinduced proton transfer coupled with energy transfer: Mechanism of sensitized luminescence of terbium ion by salicylic acid doped in polymer

In the present work, excited state intramolecular proton transfer (ESIPT) in salicylic acid (SA) monoanion and subsequent sensitization of Tb(3+) ion in polyvinyl alcohol (PVA) have been studied. The study has been carried out both by steady state and time domain fluorescence measurement techniques at room temperature. It is found that the SA completely ionizes and exists as monoanion in PVA. It exhibits a large Stokes shifted blue emission (10 000 cm(-1)) due to ESIPT and shows a decay time of 6.85 ns. On the other hand, Tb(3+) ion shows a very weak green emission and a decay time of approximately 641 mus in PVA film. Upon incorporating Tb(3+) ion in SA doped PVA film, both intensity and decay time of SA decrease and sensitized emission from Tb(+3) ion along with 3.8 mus rise time is observed. Energy transfer is found to take place both from excited singlet as well as triplet states. A brief description of the properties of the present system from the viewpoint of luminescent solar collector material is addressed.