title: Synthesis and photophysics of extended π-conjugated systems of substituted 10-aryl-pyrenoimidazoles.
abstract: The synthesis of π-extended 10-aryl-pyrenoimidazoles having different substituents was realised via Ru(ii)-catalyzed oxidative annulation of 10-aryl-pyrenoimidazole with diphenylacetylene. The single crystal X-ray structure of trifluoromethyl and carboxylate substituted annulated-10-aryl-pyrenoimidazoles confirms the near coplanarity of the pyrene and imidazole moieties and the presence of twisted conformation resulting in intermolecular C-Hπ interactions. The lowest energy absorption maximum becomes red-shifted characteristic to the nature of the substituent owing to the extended π-conjugation, and specifically the nitro substituent shows intense absorption in the visible region with the maximum at 440 nm. All the molecules were found to show intense fluorescence both in solution and solid states. Strikingly, 170 nm red-shifted fluorescence with a large Stokes shift ca. 7000 cm-1for the nitro derivative, a value nearly two-fold higher than the parent compound despite its rigid polyaromatic skeleton was observed. The combination of electron rich π-conjugated aromatic systems with electron deficient substituents induces the intramolecular charge transfer interactions, which has been corroborated with the theoretical calculations.
authors.affiliation: Department of Chemistry, School of Advanced Sciences, VIT University, Vellore, Tamil Nadu 632014, India. velan.g@vit.ac.in.
authors.forename: Shanmugam
authors.initials: S
authors.lastname: Karthik
authors.affiliation: Inorganic & Physical Chemistry Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India. moorthi@clri.res.in.
authors.forename: Joseph
authors.initials: J
authors.lastname: Ajantha
authors.affiliation: Department of Chemistry, Indian Institute of Technology Ropar, Punjab 140001, India.
authors.forename: C M
authors.initials: CM
authors.lastname: Nagaraja
authors.affiliation: Inorganic & Physical Chemistry Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India. moorthi@clri.res.in.
authors.forename: Shanmugam
authors.initials: S
authors.lastname: Easwaramoorthi
authors.affiliation: Department of Chemistry, School of Advanced Sciences, VIT University, Vellore, Tamil Nadu 632014, India. velan.g@vit.ac.in.
authors.forename: Thirumanavelan
authors.initials: T
authors.lastname: Gandhi