title: 2-amino-4-nitroaniline, a known compound with unexpected properties.
abstract: 2-amino-4-nitroaniline crystallizes in a noncentrosymmetric space group, which gives it significant potential for second-order nonlinear optical properties (NLO) in the bulk. Crystallographic and linear-polarized IR-spectrocopic data in the solid state unambiguously confirm a quinoide-like structure in the ground state in contrast to UV and theoretical data, which indicate an aromatic one for the excited state. UV-vis spectral elucidations in solutions with different polarities indicate a significant charge-transfer band with shifts of up to 100 nm, corresponding to a large value for the molecular first hyperpolarizability. Calculations of the UV- and IR-spectroscopic properties confirm the stabilization of the quinoide-like structure in the ground state, as well as the theoretically predicted NLO properties at the molecular level and provide a value of beta(tot), which is some 3.6 times higher than the analogous parameter for p-nitroaniline, a classical compound with experimentally confirmed NLO properties.
authors.affiliation: Institute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. build. 9, 1113 Sofia, Bulgaria. kolev@ orgchm.bas.bg
authors.forename: Tsonko
authors.initials: T
authors.lastname: Kolev
authors.forename: Bojidarka B
authors.initials: BB
authors.lastname: Koleva
authors.forename: Michael
authors.initials: M
authors.lastname: Spiteller
authors.forename: Heike
authors.initials: H
authors.lastname: Mayer-Figge
authors.forename: William S
authors.initials: WS
authors.lastname: Sheldrick