Kjaer Christina, Vu-Phung André, Toft Lindkvist Thomas, Langeland Jeppe, Brøndsted Nielsen Steen
Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark.
Chemistry. 2023 Oct 26;29(60):e202302166. doi: 10.1002/chem.202302166. Epub 2023 Sep 21.
The internal electronic communication between two or more light-absorbers is fundamental for energy-transport processes, a field of large current interest. Here the intrinsic photophysics of homo- and heterodimers of rhodamine cations were studied where just two methylene units bridge the dyes. Gas-phase experiments were done on frozen molecular ions at cryogenic temperatures using the newly built LUNA2 mass spectroscopy setup in Aarhus. Both absorption (from fluorescence excitation) and dispersed-fluorescence spectra were measured. In the gas phase, there is no dielectric screening from solvent molecules, and the effect of charges on transition energies is maximum. Indeed, bands are redshifted compared to those of monomer dyes due to the electric field that each dye senses from the other in a dimer. Importantly, also, as two chemically identical dyes in a homodimer do not experience the same field along the long axis, each dye has separate absorption. At low temperatures, it is therefore possible to selectively excite one dye. Fluorescence is dominantly from the dye with the lowest transition energy no matter which dye is photoexcited. Hence this work unequivocally demonstrates Förster Resonance Energy Transfer even in homodimers where one dye acts as donor and the other as acceptor.
两个或多个光吸收体之间的内部电子通信对于能量传输过程至关重要，这是当前一个备受关注的领域。在此，我们研究了罗丹明阳离子同二聚体和异二聚体的本征光物理性质，其中仅两个亚甲基单元连接染料。使用奥尔胡斯新建的LUNA2质谱装置，在低温下对冷冻的分子离子进行了气相实验。测量了吸收光谱（来自荧光激发）和色散荧光光谱。在气相中，不存在溶剂分子的介电屏蔽，电荷对跃迁能量的影响最大。实际上，由于二聚体中每个染料从另一个染料感受到的电场，与单体染料相比，谱带发生了红移。同样重要的是，由于同二聚体中两个化学性质相同的染料沿长轴感受到的场不同，每个染料都有单独的吸收。因此，在低温下，可以选择性地激发一种染料。无论哪个染料被光激发，荧光主要来自跃迁能量最低的染料。因此，这项工作明确证明了即使在同二聚体中也存在Förster共振能量转移，其中一种染料作为供体，另一种作为受体。
