Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye.

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD.

Rotational diffusion of coumarins: a dielectric friction study.

The rotational diffusion of three probes: coumarin 522B (C522B), coumarin 307 (C307) and coumarin 138 (C138) with nearly identical size was studied at room temperature employing steady-state and time-resolved fluorescence anisotropy techniques in series of alcohols and alkanes. Experimental observations indicate faster rotation of C138 compared to the other two dyes in alcohols and a faster rotation of C522B than C307 in alkanes. The dielectric friction theories of Nee-Zwanzig (NZ) and van der Zwan-Hynes (ZH) were employed to estimate the friction experienced by the probes in alcohols, in addition to the mechanical friction calculated using Stokes-Einstein-Debye (SED) hydrodynamic with slip boundary condition and Dote-Kivelson-Schwartz (DKS) quasihydrodynamic theories. The observed reorientation times for the three probes do not follow the trend predicted by dielectric friction theories of NZ and ZH. The dipole moments determined from solvatochromic techniques were found to be different for the three probes.