Time-Resolved Spectral Investigation of Bacteriochlorophyllaand Its Transmetalated Derivatives [Zn]-Bacteriochlorophyllaand [Pd]-Bacteriochlorophylla

Abstract

The lowest excited singlet (S1) and triplet (T1) states of bacteriochlorophyll a (BChl) and its central metal derivatives [Zn]- and [Pd]- BChl were investigated by femtosecond time-resolved absorption and fluorescence spectroscopy. In contrast to previously reported dynamic solvation effects on the picosecond time scale for BChl, no short kinetic components were observed for BChl and [Zn]-BChl provided that photochemical transformations of the pigments caused by multiple excitation are avoided. The S1 lifetimes of 2.6 ns, 2.1 ns, and 65 ps for BChl, [Zn]-BChl and [Pd]-BChl, respectively, are dominated by intersystem crossing (ISC) to the triplet state T1. The respective triplet quantum yields amount to 76%, 85%, and >99%. The data support that [Pd]-BChl is a highly efficient photosensitizer for photodynamic tumor therapy.

Ultrafast excited state dynamics of monomeric bacteriochlorophyll a

“…The Q y fluorescence decays mono-exponentially, and then the decay time was determined to be 3.6±0.05 ns. The determined Q y lifetime in this study agrees with the reported value [13,16,30]. The results are summarized in Tab.…”

“…Positive absorbance change was also observed immediately after excitation. These broad absorbance change has been previously assigned to the transient absorption from Q y to a higher-lying excited state (hereafter we will refer to this transient absorption as the Q y transient absorption) [13,14]. A comparison of the photo-induced absorption spectra taken at 0.1 ps shows the marked difference between excitation to the Q x band at 2.17 eV and to the Q y band at 1.59 eV, whereas the photoinduced absorption spectra taken at 1.0 and 10 ps show the similar spectral feature both after excitation to the Q x and Q y bands.…”

“…The two lowest excited states designated as the Q x and Q y states play key roles in the primary stages of light-harvesting because they act as acceptors of energy transduction from carotenoids [11]. In contrast to the intensive studies of the Q y excited state dynamics of Bchl a [12][13][14][15][16], the dynamics of the Q x state has been poorly understood because of its extremely fast decay [17][18][19]. Previous studies have suggested that deactivation of the Q x state takes place in the range between 100~400 fs, while a detailed dynamics of the Q x state has not been sufficiently understood.…”

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum

“…The first EADS is associated with the effective lifetime (s eff ) of the B800. Since, B800s are monomeric BChl molecules with an intrinsic lifetime (s int ) of *2.9 ns at RT (Connolly et al 1982;Musewald et al 1998;Niedzwiedzki and Blankenship 2010) it is apparent that ultrafast energy transfer to the B850 exciton state occurs. Simple calculation of B800 state decay rates (1/s eff = 1/s int ?…”

PDT-related photophysical properties of conformationally distorted palladium(II) porphyrins

“…This effect is especially important in the case of palladium or platinum complexes, which are used as very effective luminescence markers [5][6][7][8]. Recently, a palladium(II) bacteriochlorophyll complex has been proposed as a PDT sensitizer [9]. Moreover, palladium(II) porphyrins may become important as protein cross-linking mediators [10].…”