A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent‐Induced Increase of the Enantiomerization Barrier in 1‐Aza‐[5]helicene

Caronna, Tullio; Famulari, Antonino; Mendola, Daniele; Fontana, Francesca; Juza, Markus; Kamuf, Matthias; Zawatzky, Kerstin; Trapp, Oliver

doi:10.1002/chem.201502288

Cited by 27 publications

(39 citation statements)

References 75 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Subjecting 4 b and 4 c to HPLC on a chiral column afforded well‐resolved chromatograms, i. e., each peak was attributable to their P ‐ and M ‐isomers, respectively (Figure ‐(b): [b‐1] for 4 b and [b‐2] for 4 c ) . Bulk optical resolution of stable 2,3‐isomer 4 b was achieved by preparative HPLC .…”

Section: Resultsmentioning

confidence: 99%

Thiophene‐Fused Dinaphthopentaphenes: Versatile Applications of 1,2‐Bis(pyren‐2‐yl)aromatics in the Synthesis of π‐Expanded Molecules

et al. 2017

View full text Add to dashboard Cite

Thiophene‐fused dinaphtho[8,1,2‐opq:2′,1′,8′‐uva]pentaphenes (DNPPs) were synthesized and characterized by using our previously reported strategy. The Suzuki‐Miyaura coupling of the boronic acid ester of pyrene with dibromothiophenes, 2,3‐dibromo‐ and 3,4‐dibromothiophenes, afforded the corresponding bis(pyren‐2‐yl)thiophenes. The subsequent oxidation reaction afforded the desired π‐expanded molecules. Reflecting the DNPP moieties, the obtained molecules show properties characteristic of π‐expanded molecules, such as amphoteric multiredox behaviors and light absorption in the visible region. The oxidized product of 3,4‐bis(pyren‐2‐yl)thiophene, which contains an ortho‐quinoidal structure, i. e., benzo[c]thiophene, was isolated and spectroscopically characterized. Because these molecules possess the [5]helicene structure, optical resolution of enantiomers has been carried out using high‐performance liquid chromatography.

show abstract

Section: Resultsmentioning

confidence: 99%

Thiophene‐Fused Dinaphthopentaphenes: Versatile Applications of 1,2‐Bis(pyren‐2‐yl)aromatics in the Synthesis of π‐Expanded Molecules

et al. 2017

View full text Add to dashboard Cite

show abstract

“…91 Table 4. Activation parameters of the enantiomerization of aza [5]helicenes 35a 1-7 , carbo [5]helicene 36, and carbo [6]helicene 3 obtained by DHPLC 90 together with calculated enantiomerization barriers. Halflife times of racemization of 35a 1 , 35a 3-6 obtained by ECD spectroscopy.…”

Section: Oxidative Photocyclizationmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

View full text Add to dashboard Cite

In this review, we discuss the rich chemistry of helicenes and helicenoids containing maingroup elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, emission, together with other photochemical properties and applications. OUTLINE 14 The absorption spectrum of 19c recorded in CH 2 Cl 2 solutions exhibited a maximum at 376 nm which is significantly red shifted compared with that of double [5]helicene 19a (310 nm) due to the more extended π-conjugation in 19c. According to TD-DFT calculations, the low-energy absorption band from 400 to 500 nm is assignable to the HOMO→LUMO transition corresponding to a π−π* transition of the fully conjugated bis-helical system. DFT calculations revealed a very high theoretical isomerization barrier of 45.1 kcal/mol for the (P,P)/(M,M)-19c stereoisomer, i.e. 4.4 kcal/mol higher than the (P,M) stereoisomer (not observed experimentally). The high configurational stability of 19c enabled to obtain the pure (P,P)and (M,M)-19c by chiral HPLC (Daicel Chiralcel IE column; EtOAc/MeOH = 9:1 as eluent) and to study their chiroptical properties. The ECD spectrum of (P,P)-19c in CH 2 Cl 2 displayed two strong positive bands at 275 and 320 nm, a strong negative one at 375 nm and a broad and less intense one between 425-475 nm. 52 Note that the isomerization barrier of the OBO-fused double [7]helicene is much higher than for oxabora[6]helicene 9 (vide supra) and higher than carbo[7]helicene (42.0 kcal/ mol), indicating the advantage of double helicenes over monohelicenes in terms of conformational stability. Indeed no racemization was observed upon heating enantiomer (P,P) and (M,M)-19c for 24 h up to 200 °C. 52 Note that in 2017 a longer double OBO-helicene analogue was deposited on a Au(111) under UHV conditions and its surface-assisted cyclodehydrogenation into a planar OBO-perihexacene was observed by STM. 54 Similarly to 6 and 9, the strong bond alternation found in the BOC4 rings of 19a 51 may account for the small NICS value of 1.3 while the surrounding C6 rings, including the distorted central benzene ring, show large negative NICS values (Scheme 3c). For comparison, in the all-carbon analogue tetrabenzo-[a,f,j,o]perylene shown in Scheme 3c, the central C6 ring shows a positive NICS value, indicating substantial antiaromatic character. Notably, molecular orbital calculations of 19a indicate that the HOMO and LUMO are spread over the C6 rings rather than on the boron and oxygen atoms, accounting for the substantial stability of 19a (Scheme 3c). Borahelicenes are efficient blue fluorophores. Indeed, azabora[6]helicene 6 displays blue fluorescence at 447 nm (Table 2), while smaller achiral [4]helicenic systems were successfully used as host materials in phosphorescent OLEDs with efficiencies better than the classical 4,4'...

show abstract

“…9 The wait, however, was worth it, since access to the entire series has provided compelling evidence that judicious placement of the nitrogen atom within the helical framework can be used to selectively modulate a wide-range of physicochemical properties of these valuable molecules. 10 Building on this exceptional body of work, we recently embedded viologen functionality into [5]helicene. 11 (Figure 1) Addition of the viologen functional group simultaneously generates a redox addressable helicene, [12][13][14] a fluorescent organic salt, 15,16 and a potent photoacid, [17][18][19] which are properties of current interest for device construction.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, computational, and photophysical characterization of diaza-embedded [4]helicenes and pseudo[4]helicenes and their pyridinium and viologen homologues

et al. 2017

View full text Add to dashboard Cite

Synthesis of three [4]heli-viologens and their helical precursors, and two "pseudo-[4]helicenes" and their alkylated derivatives, which have potential device and catalysis applications, are reported. Their structures and racemization barriers have been explored with the B3LYP/6-311+G(2d,p), M06-2X/6-311+G(2d,p), and M11/6-311+G(2d,p) computational models. The photophysical properties of the helicenes and pseudo-helicenes and their alkylated derivatives have been measured. Unusual singlet-triplet energy gaps, EST, were measured and discussed for the charged alkylation products.

show abstract

A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent‐Induced Increase of the Enantiomerization Barrier in 1‐Aza‐[5]helicene

Cited by 27 publications

References 75 publications

Thiophene‐Fused Dinaphthopentaphenes: Versatile Applications of 1,2‐Bis(pyren‐2‐yl)aromatics in the Synthesis of π‐Expanded Molecules

Thiophene‐Fused Dinaphthopentaphenes: Versatile Applications of 1,2‐Bis(pyren‐2‐yl)aromatics in the Synthesis of π‐Expanded Molecules

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Synthesis, computational, and photophysical characterization of diaza-embedded [4]helicenes and pseudo[4]helicenes and their pyridinium and viologen homologues

Contact Info

Product

Resources

About