Enhanced energy transfer from diolefinic laser dyes to meso-tetrakis (4-sulfonatophenyl) porphyrin immobilized on silver nanoparticles: DFT, TD-DFT and spectroscopic studies

Abstract

Porphyrin derivatives are known singlet oxygen sensitizers in photodynamic therapy (PDT). Energy transfer from a class of diolefinic laser dyes (DOLDs) as energy donors to the sodium salt of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) as the accepter of energy would extend the range of photon harvesting down to the UV-region. Energy transfer was substantially enhanced in the presence of metallic silver nanoparticles (AgNPs), as revealed by steady-state emission spectroscopy, lifetimes, and quantum mechanics. DOLDs under investigation are 2,5distyrylpyrazine (DSP), 1,4-bis (b-pyridyl-2 vinyl) benzene (P2VB), and 1,4 bis (2-methylstyryl) benzene (MSB) as efficient donors of intense absorption in the UV-region. AgNPs enhance the rate of energy transfer from DOLDs to TPPS via bringing donor and acceptor into close-proximity with a concomitant increase in dipole-dipole interaction between excited state donor and ground-state acceptor. The DOLDs molecular structures were optimized using the DFT/CAM-B3LYP/6-311G ++ (d, p) level of theory. The calculated electronic absorption spectra for the studied DOLDs in the gaseous phase and methanol solvent were studied using the time-dependent density functional theory (TD-DFT) at M06-2X/6-311G++ (2d,2p) level. The calculated absorption/emission spectra for DSP laser dye in methanol are obtained at the TD/ M06-2X/6-311G++(2d, 2p) method. Nota-bly, all theoretical results of the molecular structures under study highly agreed with the practical optical results. Energy transfer rate constants (kET) amid energy donor/acceptor pairs were deter-mined by Stern-Volmer constants (KSV) and donors' lifetime measurements. The KSV values indi-cate an enhanced Fluorescence Resonance Energy Transfer (FRET) efficiencies in the presence of negatively charged AgNPs. The critical transfer distances Ro were determined from the spectral overlap between the emission spectrum of donor and absorption spectrum of TTPS. These out-comes propose the application of designed metal-enhanced FRET for energy-transfer-based assays and photodynamic therapy (PDT) applications.