Cyanobacterial photosystem I (PSI) constitutes monomeric and trimeric pigment–protein complexes whose optical properties are marked by the presence of long-wavelength absorption bands. In spite of numerous experimental studies, the nature of these bands is still under debate and requires intensive theoretical analysis. Collecting together the data of linear spectroscopy and single-molecule spectroscopy (SMS) of PSI from Arthrospira platensis, we performed quantum modeling of the optical response based on molecular exciton theory (ET) and the multimode Brownian oscillator model (MBOM). Applying MBOM, the spectra of the red antenna state were calculated considering a particular for each red state adjustment of the low-frequency vibronic modes. Within the framework of our PSI exciton model it was shown that the coupling energy between antenna chlorophylls cannot be a factor of the red states formation, thus the long-wavelength bands are calculated without attribution to so-called antenna red chlorophylls. By the fitting of Huang–Rhys factors and frequencies for the lowest vibronic modes, we were able to reproduce the effects of strong and weak electron–phonon coupling experimentally observed in SMS spectra of red antenna states. Based on our theoretical calculations and also analysis of existing crystal structures of cyanobacterial PSI, we assumed that long-wavelength Chls can be localized in the peripheral protein subunits containing one or two pigment molecules.

蓝藻光系统 I (PSI) 构成单体和三聚体色素-蛋白质复合物，其光学特性以长波长吸收带的存在为标志。尽管进行了大量实验研究，但这些波段的性质仍在争论中，需要深入的理论分析。收集来自钝顶藻的 PSI 的线性光谱和单分子光谱 (SMS) 数据，我们基于分子激子理论 (ET) 和多模布朗振荡器模型 (MBOM) 对光响应进行了量子建模。应用 MBOM，考虑到低频振动模式的每个红色状态调整的特殊情况，计算红色天线状态的光谱。在我们的 PSI 激子模型的框架内，表明天线叶绿素之间的耦合能量不能成为红色状态形成的一个因素，因此计算长波长带时不归因于所谓的天线红色叶绿素。通过拟合最低振动模式的 Huang-Rhys 因子和频率，我们能够重现在红色天线状态的 SMS 光谱中实验观察到的强和弱电子 - 声子耦合的影响。