Geacintov N E, Breton J
Biophys J. 1977 Jan;17(1):1-15. doi: 10.1016/S0006-3495(77)85623-3.
The fluorescence yield (F) of spinach chloroplasts at 100 degrees K measured at 735 nm (photosystem I fluorescence-F 735) and at 685 nm (photosystem II fluorescence-F 685) has been determined with different modes of laser excitation. The modes of excitation included a single picosecond pulse, sequences of picosecond pulses (4, 22, and 300 pulses spaced 5 ns apart) and a single nonmode-locked 2-mus pulse (MP mode). The F 735/F 685 intensity ratios decrease from 1.62 to 0.61 when a single picosecond pulse (or low-power continuous helium-neon laser) is replaced by excitation with the 300-ps pulse train (PPT mode) or MP mode. In the PPT mode of excitation, the 735-nm fluorescence band is quenched by a factor of 45 as the intensity is increased from 10(15) to 10(18) photons/cm(2) per pulse train and the 685-nm fluorescence is quenched by a factor of 10. In the MP mode, the quenching factors are 25 and 7, respectively, in the same intensity range. Fluorescence quantum yield measurements with different picosecond pulse sequences indicate that relatively long-lived quenching species are operative, which survive from one picosecond pulse to another within the pulse train. The excitonic processes possible in the photosynthetic units are discussed in detail. The differences in the quenching factors between the MP and PPT modes of excitation are attributed to singlet-singlet annihilation, possible when picosecond pulses are utilized, but minimized in the MP mode of excitation. The long-lived quenchers are identified as triplets and/or bulk chlorophyll ions formed by singlet-singlet annihilation. The preferential quenching in photosystem I is attributed to triplet excitons. The influence of heating effects, photochemistry, bleaching, and two-photon processes is also considered and is shown to be negligible.
在100K温度下，利用不同模式的激光激发，测定了菠菜叶绿体在735nm（光系统I荧光 - F735）和685nm（光系统II荧光 - F685）处的荧光产率（F）。激发模式包括单个皮秒脉冲、皮秒脉冲序列（4个、22个和300个脉冲，间隔5ns）以及单个非锁模2 - μs脉冲（MP模式）。当用300 - ps脉冲序列（PPT模式）或MP模式激发取代单个皮秒脉冲（或低功率连续氦氖激光）激发时，F735/F685强度比从1.62降至0.61。在PPT激发模式下，随着每个脉冲序列的强度从10(15)增加到10(18)光子/cm(2)，735 - nm荧光带被猝灭45倍，685 - nm荧光被猝灭10倍。在MP模式下，在相同强度范围内，猝灭因子分别为25和7。用不同皮秒脉冲序列进行的荧光量子产率测量表明，存在相对长寿命的猝灭物种，它们在脉冲序列中从一个皮秒脉冲存活到另一个皮秒脉冲。详细讨论了光合单位中可能的激子过程。MP和PPT激发模式之间猝灭因子的差异归因于单重态 - 单重态湮灭，这在使用皮秒脉冲时可能发生，但在MP激发模式下被最小化。长寿命猝灭剂被确定为通过单重态 - 单重态湮灭形成的三重态和/或整体叶绿素离子。光系统I中的优先猝灭归因于三重态激子。还考虑了热效应、光化学、漂白和双光子过程的影响，结果表明这些影响可忽略不计。
