title: Highly emissive luminogens based on imidazo[1,2-a]pyridine for electroluminescent applications.
abstract: A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2-a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A(3) coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2-a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2-a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3 =tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m(-2).
authors.affiliation: School of Chemistry, Bharathidasan University, Tiruchirappalli, 620 024, Tamil Nadu (India), Fax: (+91) 431-2407045.
authors.forename: Natarajan
authors.initials: N
authors.lastname: Nagarajan
authors.forename: Gunasekaran
authors.initials: G
authors.lastname: Velmurugan
authors.forename: Asit
authors.initials: A
authors.lastname: Prakash
authors.forename: Nanda
authors.initials: N
authors.lastname: Shakti
authors.forename: Monica
authors.initials: M
authors.lastname: Katiyar
authors.forename: Ponnambalam
authors.initials: P
authors.lastname: Venuvanalingam
authors.forename: Rajalingam
authors.initials: R
authors.lastname: Renganathan
mesh_terms: D055664:Electrochemical Techniques; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D008163:Luminescent Measurements; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D011725:Pyridines; C001439:imidazo(1,2-a)pyridine
keywords: density functional calculations; donor-acceptor systems; dyes/pigments; fluorescence; nitrogen heterocycles