Fluorescence of the helicenes

Dibenzo[7]helicenes were synthesized with up to 99 % ee by rhodium(I)/binap-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2-phenylnaphthalene-linked triynes. Additionally, [2+1+2+1] cycloaddition products, that is, twisted anthracenes, were also synthesized by using difluorphos as ligand. Although these compounds are not configurationally stable at elevated temperature, their Scholl reactions afforded configurationally stable double dibenzo[6]helicenes. The thus-obtained dibenzo[7]helicene exhibited good circularly polarized luminescence property and the double dibenzo[6]helicene showed high fluorescence quantum yield.

Section: Resultsmentioning

confidence: 72%

Synthesis of Single and Double Dibenzohelicenes by Rhodium‐Catalyzed Intramolecular [2+2+2] and [2+1+2+1] Cycloaddition

Yamano

Shibata

Tanaka

2018

“…Helicene quinones 3 and 6 showed relatively weak luminescence (Figure S8 in the Supporting Information), compared to the intact [6]helicene, with fluorescence quantum yields ϕ F =0.02 and 0.008, respectively. The luminescence of helicenes 3 and 6 was strongly quenched by atmospheric oxygen (Figure S9 in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…The spectrum of (P)-(+ +)-3 is almost identical to the one of (P)-(+ +)-6 with only slight differences of the Cotton effect in the UV region.A sa nticipated, the phenyl substituent has only am inor influence on the chiroptical properties of (P)-(+ +)-6. [5g] Helicene quinones 3 and 6 showed relatively weak luminescence ( Figure S8 in the Supporting Information), comparedt o the intact [6]helicene, [20] with fluorescenceq uantum yields f F = 0.02 and 0.008, respectively.T he luminescence of helicenes 3 and 6 was strongly quenched by atmospherico xygen (Figure S9 in the Supporting Information). This behavior is in line with an efficacious intersystem crossing to the triplet excited state, which is observed for [4]-[9]helicenes (f T = 0.91).…”

Section: Electrochemistrychiroptical Properties and (Td-)dft Calculmentioning

confidence: 99%

Electronic Structures and Chiroptical Properties of Post‐functionalized Helicene Quinones

Schweinfurth

Mazzolini

Neshchadin

et al. 2016

The synthesis of redox-active p- and o-quinones 2-phenylamino-4-phenylimino[6]helicene-1-one 1, 2-phenylamino[6]-helicene-1,4-dione 2, and 4-phenyl[6]helicene-1,2-dione 3 in their enantiopure forms by post-functionalization of (P)- and (M)-1,2-dimethoxy[6]helicene is presented. Structural characterization in solution and in the solid state was accomplished by 2D NMR spectroscopy methods and X-ray diffraction analysis, respectively. Interpretation of electrochemical redox data was accompanied by a detailed orbital picture, derived from DFT calculations. The electronic structures of compounds 1-3 were investigated by UV/Vis and electronic circular dichroism (ECD) spectroscopy, complemented by TD-DFT calculations. Quinones 1-3 were chemically reduced to study the EPR signatures of their respective radical anions. DFT methods were used for the atom assignment of the hyperfine coupling constants. The results are discussed within the context of electrochromic chiral switches and molecular recognition.

“…324 and 390 nm for [6]‐ and [9]helicenes, respectively) . To make matters worse, fluorescence quantum yields Φ FL of [ n ]carbohelicenes significantly decrease on increasing the size n ( Φ FL ≤0.02 for n ≥7), and this discourages the utilization of simple helicenes for CPL in the far‐red region . In contrast, improved chiroptical properties of dipyrromethene chromophores have been recently reported, and the supramolecular dimer was shown to be more promising .…”

Section: Introductionmentioning

confidence: 99%

Significant Enhancement of Absorption and Luminescence Dissymmetry Factors in the Far‐Red Region: A Zinc(II) Homoleptic Helicate Formed by a Pair of Achiral Dipyrromethene Ligands

Ito

Sakai

Okayasu

et al. 2018

A homoleptic zinc(II) helicate organized by a pair of achiral dipyrromethene ligands through zinc(II) coordination was synthesized to evaluate the chiroptical properties. This zinc complex showed strong exciton-coupled chiroptical responses from the helical configuration with a large absorption dissymmetry factor |g | (up to 0.20). More importantly, intense polarized luminescence in the far-red region (700-850 nm) with a fluorescence quantum yield Φ of 0.23 was observed for this helicate with a dissymmetry factor |g | of 0.022, the largest value among rare-earth- and precious-metal-free small molecules. These unprecedentedly large g values were supported by theoretical calculations.