Single-Molecule Spectroscopic Investigation of Energy Migration Processes in Cyclic Porphyrin Arrays

Abstract

Covalently linked cyclic porphyrin arrays have been synthesized to mimic natural light-harvesting apparatuses and to investigate the highly efficient energy migration processes occurring in these systems for future applications in molecular photonics. To avoid an ensemble-averaged picture, we performed a single-molecule spectroscopic study on the energy migration processes of cyclic porphyrin arrays and a linear model compound embedded in a rigid polymer matrix by recording fluorescence intensity trajectories, by performing coincidence measurements, and by doing wide-field defocused imaging. Our study demonstrates efficient energy migration within the cyclic porphyrin arrays at the single-molecule level. By comparison with the data of the linear model compound, we could pinpoint the role of the dipole-dipole coupling between diporphyrin subunits and the rigidity of the cyclic structures on the energy transfer processes.

The Rylene Colorant Family—Tailored Nanoemitters for Photonics Research and Applications

“…[141,142] Additionally, the chromophore systems are protected from photobleaching by the presence of other molecules, for example, carotenoids. [143][144][145] The introduction of strong and weak coupling as well as protective units in one molecular system is at present out of reach for synthetic chemistry and, therefore, we focused first on achieving a cascade of energy transfer by spatially arranging arrays of FRET-donor and FRETacceptor molecules.…”

The Role of Electronic Coupling in Linear Porphyrin Arrays Probed by Single‐Molecule Fluorescence Spectroscopy

“…[20][21][22][23][24][25][26][27] For this application, the photophysical properties of the molecular assemAbstract: Single-molecule photophysical properties of two families of linear porphyrin arrays have been investigated by single-molecule fluorescence detection techniques. Butadiyne-linked arrays (Z N B) with extensive p-conjugation perform as photostable one-quantum systems.…”

Excitation energy migration processes in various multi-porphyrin assemblies

“…1 The EET rate between neighbouring Z4 subunits in C24ZB was determined similarly by TAA measurements to be 36 ps −1 (scheme 4), which is almost the same as that of the reference molecule 2Z4 [15,17]. A large difference between the EET rates of C12ZA and C24ZB is explained in terms of a large difference in the centre-to-centre distance of meso-meso linked porphyrin subunits: the distance of C24ZB is ca 1.5-fold longer than that of C12ZA, which, on the basis of the distance factor of R −6 in the Förster EET equation, explains well the approximately 10 times difference in the observed EET rates.…”

“…In the absorption spectra of C N ZA, the peak positions of lowenergy Soret bands converge into a single position, which originates from exciton couplings among non-unidirectional transition dipole moments in circular geometries. According to this feature, it can be conceived that three-dimensional orientations between two adjacent Z2 subunits remain relatively the same in all C N ZA [17][18][19].…”

“…At the single-molecule level, the EET efficiencies of individual cyclic porphyrin arrays were examined by carrying out coincidence measurement [17,18]. This measurement allows for the observation of singlet-singlet annihilation processes occurring in a single molecule (figure 6a) [26,27].…”