Up-converted fluorescence from photosynthetic light-harvesting complexes linearly dependent on excitation intensity

Establishment of the Qy Absorption Spectrum of Chlorophyll a Extending to Near-Infrared

A weak absorption tail related to the Q_y singlet electronic transition of solvated chlorophyll a is discovered using sensitive anti-Stokes fluorescence excitation spectroscopy. The quasi-exponentially decreasing tail was, at ambient temperature, readily observable as far as -2400 cm^-1 from the absorption peak and at relative intensity of 10^-7. The tail also weakened rapidly upon cooling the sample, implying its basic thermally activated nature. The shape of the spectrum as well as its temperature dependence were qualitatively well reproduced by quantum chemical calculations involving the pigment intramolecular vibrational modes, their overtones, and pairwise combination modes, but no intermolecular/solvent modes. A similar tail was observed earlier in the case of bacteriochlorophyll a, suggesting generality of this phenomenon. Long vibronic red tails are, thus, expected to exist in all pigments of light-harvesting relevance at physiological temperatures.

Vibronic Origin of the Qy Absorption Tail of Bacteriochlorophyll a Verified by Fluorescence Excitation Spectroscopy and Quantum Chemical Simulations

The long-wavelength tail of the lowest-energy Q_y singlet absorption band of bacteriochlorophyll a in triethylamine peaking at 768.6 nm was examined by means of fluorescence excitation spectroscopy at ambient temperature of 22 ± 1 °C. The tail, usually considered a Gaussian, does in fact weaken quasi-exponentially, being clearly evident as far as 940 nm, nearly 2400 cm^-1 (∼12 k_BT) away from the absorption peak. Quantum chemical simulations identified vibronic transitions from the thermally populated normal modes and their overtones in the ground electronic state as the origin of this tail. Because energy transfer and relaxation processes generally depend on vibronic overlap integrals, these findings may have important implications on the interpretation of numerous photoinduced phenomena that involve bacteriochlorophyll and similar molecules, including photosynthesis.

Construction of specific magnetic resonance imaging/optical dual-modality molecular probe used for imaging angiogenesis of gastric cancer

The purpose of the study was to construct specific magnetic resonance imaging (MRI)/optical dual-modality molecular probe. Tumor-bearing animal models were established. MRI/optical dual-modality molecular probe was construed by coupling polyethylene glycol (PEG)-modified nano-Fe₃O₄ with specific targeted cyclopeptide GX1 and near-infrared fluorescent dyes Cy5.5. MRI/optical imaging effects of the probe were observed and the feasibility of in vivo double-modality imaging was discussed. It was found that, the double-modality probe was of high stability; tumor signal of the experimental group tended to be weak after injection of the probe, but rose to a level which was close to the previous level after 18 h (p > 0.05). We successively completed the construction of an ideal MRI/optical dual-modality molecular probe. MRI/optical dual-modality molecular probe which can selectively gather in gastric cancer is expected to be a novel probe used for diagnosing gastric cancer in the early stage.