title: Photophysical properties of β-substituted free-base corroles.
abstract: Corroles are an emergent class of fluorophores that are finding an application and reaction chemistry to rival their porphyrin analogues. Despite a growing interest in the synthesis, reactivity, and functionalization of these macrocycles, their excited-state chemistry remains undeveloped. A systematic study of the photophysical properties of β-substituted corroles was performed on a series of free-base β-brominated derivatives as well as a β-linked corrole dimer. The singlet and triplet electronic states of these compounds were examined with steady-state and time-resolved spectroscopic methods, which are complemented with density functional theory (DFT) and time-dependent DFT calculations to gain insight into the nature of the electronic structure. Selective bromination of a single molecular edge manifests in a splitting of the Soret band into x and y polarizations, which is a consequence of asymmetry of the molecular axes. A pronounced heavy atom effect is the primary determinant of the photophysical properties of these free-base corroles; bromination decreases the fluorescence quantum yield (from 15% to 0.47%) and lifetime (from 4 ns to 80 ps) by promoting enhanced intersystem crossing, as evidenced by a dramatic increase in knr with bromine substitution. The nonbrominated dimer exhibits absorption and emission features comparable to those of the tetrabrominated derivative, suggesting that oligomerization provides a means of red-shifting the spectral properties akin to bromination but without decreasing the fluorescence quantum yield.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Lemon
authors.forename: Robert L
authors.initials: RL
authors.lastname: Halbach
authors.forename: Michael
authors.initials: M
authors.lastname: Huynh
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D065966:Absorption, Physicochemical; D018360:Crystallography, X-Ray; D019281:Dimerization; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000737:chemistry*; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
chemical_list: D011166:Porphyrins; C431863:corrole