The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlorophyll a complexes (exciplexes) was monitored by measuring the electrochromic shift of β-carotene in the spectral range 500–510 nm. The excitation of high-energy chlorophyll in light-harvesting antenna of both species was not accompanied by immediate appearance of an electrochromic shift. In PS I from T. elongatus, the excitation of long-wavelength chlorophyll (LWC) caused a pronounced electrochromic effect at 502 nm assigned to the appearance of CT states of chlorophyll exciplexes. The formation of ion-radical pair P₇₀₀⁺A₁⁻ at 40 ps was limited by energy transfer from LWC to the primary donor P₇₀₀ and accompanied by carotenoid bleach at 498 nm. In PS I from Synechocystis 6803, the excitation at 720 nm produced an immediate bidentate bleach at 690/704 nm and synchronous carotenoid response at 508 nm. The bidentate bleach was assigned to the formation of primary ion-radical state P_B⁺Chl_2B⁻, where negative charge is localized predominantly at the accessory chlorophyll molecule in the branch B, Chl_2B. The following decrease of carotenoid signal at ~ 5 ps was ascribed to electron transfer to the more distant molecule Chl_3B. The reduction of phylloquinone in the sites A_1A and A_1B was accompanied by a synchronous blue-shift of the carotenoid response to 498 nm, pointing to fast redistribution of unpaired electron between two branches in favor of the state P_B⁺A_1A⁻.

光系统 I (PS I) 复合物中的能量和电荷转移过程从蓝细菌Thermosynechococcus elongatus和Synechocystis sp. 中分离出来。PCC 6803 通过泵到探针飞秒光谱进行了研究。通过测量β-胡萝卜素在 500-510 nm 光谱范围内的电致变色位移来监测激子耦合叶绿素a复合物（exciplexes）中电荷转移 (CT) 状态的形成。两种物种的捕光天线中高能叶绿素的激发并未立即出现电致变色位移。在来自T. elongatus 的PS I，长波长叶绿素 (LWC) 的激发在 502 nm 处引起了明显的电致变色效应，这归因于叶绿素激发复合物的 CT 状态的出现。离子-自由基对 P ₇₀₀ ⁺ A ₁ ^-在 40 ps 的形成受到从 LWC 到主要供体 P ₇₀₀的能量转移的限制，并伴有 498 nm 的类胡萝卜素漂白。在来自集胞藻6803 的PS I 中，720 nm 处的激发在 690/704 nm 处产生立即双齿漂白，在 508 nm 处产生同步类胡萝卜素响应。二齿漂白剂被指定为形成初级离子自由基状态 P _B ⁺ Chl _2B ^-，其中负电荷主要位于分支 B 中的辅助叶绿素分子 Chl _{2B 处}。随后在~5 ps 时类胡萝卜素信号的降低归因于电子转移到更远的分子 Chl _3B。位点 A _1A和 A _1B中叶绿醌的减少伴随着类胡萝卜素响应同步蓝移至 498 nm，表明两个分支之间未配对电子的快速重新分布有利于状态 P _B ⁺ A _1A ^-。