On novel fluorescence in the Qx region of the bacteriochlorophyll a and chlorophyll a dimers in solution

Abstract

Pulsed laser induced fluorescence spectra of dimeric and aggregated bacteriochlorophyll a (BChl a) in solution are presented. Two fluorescence bands, at 783 and 583 nm for BChl a in hexane, are assigned to the BChl a dimer. These two bands correspond to the two fluorescence bands of the chlorophyll a (Chi a) dimer in solution at 688 and 625 nm.1 Comparison of absorption and fluorescence data for the two chlorophyll dimers allows assignment of the shorter wavelength fluorescence transitions at 625 and 583 nm to the dimer Qx transitions of the Chi a and BChl a dimers, respectively. The stronger fluorescence bands at 688 and 783 nm are the corresponding dimer Qy transitions. Qx fluorescence transitions are not observed for the monomer of either Chi a or BChl a in solution. The activity of the Qx fluorescence transitions in the dimers and the observation that the fluorescence lifetime of the Qy transition is longer than that of the Qx transition for each of the chlorophyll dimers are discussed in relation to nonradiative channels for deexcitation of the dimers and monomers.

Molecular emission and electronic structure of associated chlorophyll a

“…Chla was extracted from fresh spinach according to the method of Omata and Murata (22) and purity established by standard techniques (23,24). The pure Chla wa stored in the dark in a nitrogen-purged dry box.…”

Tapping the near-infrared spectral region with bacteriochlorin arrays

“…The NIR region has been comparatively little used in clinical diagnostics and biomedical imaging, hence, bacteriochlorins, which appear to be Nature's chosen absorbers in this spectral region, warrant extensive examination. 3 Spectroscopic studies have been performed of bacteriochlorins in a variety of assemblies and architectures including solution 4 or crystalline 5 aggregates, monolayers and thin films, 6 micelles, 7 and with a 24-residue polypeptide in micelles. 8 Bacteriochlorins also have been examined upon siteisolation in apoproteins 9 and in mesoporous silica.…”