On the Influence of the Bridge on Triplet State Delocalization in Linear Porphyrin Oligomers

Abstract

The extent of triplet state delocalization is investigated in rigid linear zinc porphyrin oligomers as a function of interporphyrin bonding characteristics, specifically in meso-meso singly linked and β,meso,β fused structures, using electron paramagnetic resonance techniques. The results are compared with those of earlier measurements on porphyrin oligomers with alkyne linkers exhibiting different preferred conformations. It is shown that dihedral angles near 90° between the porphyrin planes in directly meso-to-meso linked porphyrin oligomers lead to localization of the photoexcited triplet state on a single porphyrin unit, whereas previous work demonstrated even delocalization over two units in meso-to-meso ethyne or butadiyne-bridged oligomers, where the preferred dihedral angles amount to roughly 30° and 0°, respectively. The triplet states of fused porphyrin oligomers (i.e., porphyrin tapes) exhibit extended conjugation and even delocalization over more than two porphyrin macrocycles, in contrast to meso-to-meso ethyne or butadiyne-bridged oligomers, where the spin density distribution in molecules composed of more than two porphyrin units is not evenly spread across the oligomer chain.

Charge transport through extended molecular wires with strongly correlated electrons

“…The three bonds between each porphyrin result in a planar structure and thus enhance electron delocalization across FP3 . 22–26 The electrochemical gap of FP3 from square-wave voltammetry is 0.8 eV (as compared to 1.7 eV for a zinc porphyrin monomer with the same anchor groups 20 ). The longest wavelength absorbance maximum in the optical absorbance spectrum of FP3 is at 1500 nm (0.83 eV), compared to 700 nm (1.77 eV) for the monomer ( FP3 spectra are in the ESI † ).…”

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

“…While optical spectroscopy has proved a powerful tool to examine the photophysics and spinconversion rates in TADF 30,31,35,36 , trESR provides a complementary window into the underlying spin physics. TrESR is sensitive to paramagnetic states and can therefore probe the formation dynamics and coupling mechanisms of triplet excitons 37 , as highlighted by broad applications in studying triplet excitons in organic photovoltaics [38][39][40] , singlet fission [41][42][43][44] , photosensitizers 37,[45][46][47] , and molecular electronics 48,49 . Because trESR is not sensitive to singlet excitons (due to their diamagnetism) it can only explicitly probe forward ISC.…”

Screening Nanographene‐Mediated Inter(Porphyrin) Communication to Optimize Inter(Porphyrin–Fullerene) Forces

“…In particular, the nanosecond decay affords predominantly the evolution of the localized triplet excited state as the fourth species. [48][49][50][51][52] It takes hundreds of microseconds to deactivate the latter and to reinstate quantitatively the ground state.…”