Investigations of Chl a aggregates cross-linked by dioxane in 3-methylpentane

In this work, dioxane-bound aggregates of chlorophyll a are prepared in 3-methylpentane. The properties of the aggregates are studied by using steady-state and time-resolved spectroscopies. The Q(y)-region absorption spectrum of the chlorophyll a-dioxane aggregate shows four clearly resolvable narrow bands with comparable intensities. The band maxima are located at 683, 689, 698 and 702 nm. The emission spectrum consists of two emission bands centred at 699 and 702 nm suggesting the presence of two types of aggregates. High degree of fluorescence polarization is detected yielding the angles between the absorption transition moments with respect to the 702 nm emission transition moment. The circular dichroism signal is strong and the sign sequence follows that of the polarization spectrum. psi-type effect is discovered due to long-range interactions within the sizable aggregate frame. The insensitivity of the time-resolved emission kinetics to the temperature indicate the excitation delocalization length to be short, The rapid loss of time-resolved anisotropy at certain wavelengths supports the energy transfer to take place. The independence of the excitation spectrum over a broad range of emission wavelengths suggests that the two diverse spectral types are found within the same macro-aggregate and that they an coupled together by the energy transfer. (C) 1997 Elsevier Science B.V.