Single-molecule fluorescence dynamics of a butadiyne-linked porphyrin dimer: the effect of conformational flexibility in host polymers

Abstract

We have investigated the single-molecule fluorescence dynamics of a butadiyne-linked porphyrin dimer (Z2B) depending on the density of the poly(methyl methacrylate) (PMMA) matrix (5, 10, 25, and 50 mg ml(-1)). By recording single-molecule fluorescence intensity trajectories and fluorescence lifetimes, we observed more frequent one-step photobleaching behavior, less frequent on-off behavior, and narrower fluorescence lifetime distributions in lower densities of PMMA polymer. In contrast, more enhanced photostability was observed in higher densities of PMMA polymer. These results are explained by a difference in the molecular surroundings depending on the change in PMMA polymer density, suggesting that the individual photophysical properties of Z2B are strongly associated with their conformations and molecular surroundings in the solid state. Our studies will provide further information on the structure/surroundings relationship of single molecules in the solid state.

Panchromatic light funneling through the synergy in hexabenzocoronene–(metallo)porphyrin–fullerene assemblies to realize the separation of charges

“…However, for butadiyne-linked porphyrin dimers such as 2-Zn, the spectral changes have also been described in terms of an extended conjugated p-system across the two porphyrins and the bridge that depends on the dihedral angle between the porphyrin subunits. 36,52,53,[55][56][57][58][59] The same trends, i.e., red-shied (relative to ZnTPP) and single uorescence maxima, were found for the (metallo) porphyrin-centered features upon 450 nm photoexcitation. Only 1-Cu does not uoresce because of the open-shell character of the central metal ion.…”

“…Previous work on similar di-and tetra-substituted porphyrins and porphyrin-dimers, bearing aryl-ethynyl substituents, revealed similar effects. 22,25,[51][52][53][54] The absorption spectrum of dimeric 2-Zn also is inuenced by the factors discussed above. In addition, both the Soret-band (463 and 495 nm) and the Q-band (683 and 737 nm) absorptions are split into two, suggesting electronic coupling of the two porphyrin moieties: placing two or more porphyrins in close proximity and dened geometry, as in 2-Zn, is known to cause excitonic splitting.…”

Photoluminescence Intermittency from Single Quantum Dots to Organic Molecules: Emerging Themes

“…Since PBMA has a large nonpolar side group that hinders chain packing, more free volume is available in this polymer allowing for changes in dimer orientation [120]. Other examples of environmental effects include butadiyene linked porphyrin dimers incorporated into PMMA of different percent weights [121]. Single step photobleaching statistics were enhanced in lower-density PMMA, but blinking was less frequent.…”

Microviscosity and temperature sensors: The twists and turns of the photophysics of conjugated porphyrin dimers — a SPP/JPP Young Investigator Award paper

“…Various porphyrin dimers linked via butadiyne bridge have also been used for sensing the inner environment of polymers [56,57] and ionic liquids [58,59], via ratiometric or lifetime methods. Lee et al have performed a single-molecule fluorescence experiment with porphyrin dimer incorporated in poly(methyl methaacrylate) (PMMA) films of varying density, from 5 to 50 mg/mL [56].…”