Arjun Paudel

Pyrene-cored blue-light emitting [4]helicenes: synthesis, crystal structures, and photophysical properties.

The synthesis, crystal structures and photophysical properties of two types of pyrene-cored blue-light emitting [4]helicenes (7 and 9) are reported. The chemical structures of all synthesized compounds were fully confirmed by 1H and 13C NMR spectra, mass spectroscopy as well as elemental analysis. Single-crystal X-ray analysis of these [4]helicenes revealed that there are two types of laterally naphthalene annulated helical architectures, which are clearly influenced by different R substituents. The photophysical properties of the [4]helicenes (7 and 9) were fully investigated in both solutions and films, along with the pre-cyclization products, 4,9- and 4,10-bis(phenylethenyl)pyrenes (6 and 8). Notable optical features were obtained in these compounds, which make them promising candidates for several important applications in modern electronic and optoelectronic devices, such as blue emitters in organic light-emitting devices (OLEDs), or as models for further exploring the development of a new generation of organic materials based on pyrene.

Synthesis and structural properties of novel polycyclic aromatic compounds using photo-induced cyclisation of 2,7-di- tert -butyl-4-(phenylethenyl)pyrenes

Wittig reaction of 2,7-di-tert-butylpyrene-4-carbaldehyde with benzyltriphenylphosphonium salts in the presense of n-BuLi gave 2,7-di-tert-butyl-4-(phenylethenyl)pyrenes, from which naphthalene condensed aromatic compounds, 2,7-di-tert-butyl-dibenzo[ij, no]tetraphenes, were obtained by photo-induced cyclisation in the presense of iodine.

Synthesis and structures of [2.n]metacyclophane-1,2-diones

McMurry cyclisation of 1,n-bis(5-formyl-2-methoxyphenyl)alkanes afforded dimethoxy[2.n]metacyclophan-1-enes and dimethoxy[2.n]metacyclophane-1,2-diols, in which latter one was converted to dimethoxy[2.n]metacyclophane-1,2-diones by Albright–Goldman oxidation.

Synthesis and spectral properties of 2,7-di-tert-butyl-4,9-bis(arylethynyl)-and 4,10-bis(arylethynyl)pyrenes

Formylation of 2,7-di-tert-butylpyrene with dichloromethyl methyl ether in the presense of AlCl3 afforded a mixture of 2,7-di-tert-butylpyrene-4,9-biscarbaldehyde and 4,10-biscarbaldehyde in the ratio of 75:25, from which the corresponding bis(arylethynyl)pyrenes were obtained by the Wittig reaction with aryl methyl phosphonium ylides followed by bromination and dehydrobromination.

Electrophilic aromatic substitution of 7-t-butyl-1,3-dimethylpyrene : preparation of 5-mono-and 5,9-di-substituted 7-t-butyl-1,3-dimethylpyrenes

Formylation and acetylation of 7-t-butyl-1,3-dimethylpyrene selectively afforded the 5-mono- and 5,9-di-substitution products depending on the Lewis acid catalyst used, while bromination and nitration afforded the 6-substitution product.

Synthesis and photoreactions of polymethyl substituted [2.2]metacyclophanes

Photo-oxygenation of 4,5,6,8,12,13,14,16-octamethyl[2.2]metacyclophane using a high-pressure mercury lamp produced a mixture of mono- and bis-endoperoxides in quantitative yield, while irradiation with sunlight in chloroform afforded 1,2,3,6,7,8-hexamethyl-trans-10b,10c-dimethyl-10b,10c-dihydropyrene in 20% yield.

Synthesis of polymethyl substituted [2.2]metaparacyclophanes and their Lewis-acid induced isomerisation to [2.2]metacyclophanes

The preparation of polymethyl substituted [2.2]metaparacyclophanes using sulfur method and the X-ray structure determination of 4,5,6,8,12,13,15,16-octamethyl[2.2]metaparacyclophane are described. AlCl3-MeNO2-catalysed trans-tert-butylation of 5-tert-butyl-8,12,13,15,16-pentamethyl[2.2]metaparacyclophane in benzene led to isomerisation reaction to afford the strainless 8,12,13,14,16-pentamethyl[2.2]metacyclophane in 85% yield along with tert-butylbenzene.

ipso -Acylation of 5,13-di- tert -butyl-8,16-dimethyl[2.2]metacyclophane with acid anhydrides: through-space electronic interaction among the two benzene rings

Acylation of 5,13-di-tert-butyl-8,16-dimethyl[2.2]metacyclophane with acid anhydrides led to mono-ipso-acylation at the tert-butyl group to give 5-acyl-13-tert-butyl-8,16-dimethyl[2.2]metacyclophanes, from which the second electrophilic substitition with acid anhydrides can be strongly suppressed because of deactivation of the second aromatic ring by acyl group introduced by the through-space electronic interaction.

Synthesis and structures of 8-(tolylmethyl)[2.2]metacyclophanes and 8,8'-(ethane-1,2-diyl)bis(16-methoxy[2.2]metacyclophane)

A convenient preparation of 8-(tolylmethyl)[2.2]metacyclophanes and 8,8′-(ethane-1,2-diyl)bis(16-methoxy[2.2]meta-cyclophane) using a cross-coupling reaction of 8-bromomethyl[2.2]metacyclophanes with tolylmagnesium bromides is described. The structures of these novel [2.2]metacyclophanes in solution are also discussed.

Synthesis and conformational studies of 2,11-dithia[3]metacyclo[3](1,3)pyrenophanes: the ring current interactions derived from pyrene ring

A series of 2,11-dithia[3]metacyclo[3](1,3)pyrenophanes are obtained by the coupling reaction of the corresponding 1,3-bis(bromomethyl)pyrene and bis(sulfanylmethyl)benzenes in ethanol under the high dilution conditions. The conformational studies of dithia[3]metacyclo[3](1,3)pyrenophanes as well as the ring current interactions derived from pyrene ring are described.