Oscillatory polarons generation by near IR and spin induced chirality studies in optically nonlinear 1,3-dinitrobenzene crystal

Abstract

Paramagnetic species in the 1,3-dinitrobenzene (mDNB) crystal have been detected by EPR spectroscopy and the intervalence (conductivity) band at ∼10,400cm−1 along the polar c axis, and the band at ∼7400cm−1 along the a axis, of unknown origin, have been found in its polarized NIR spectra. The radical anions occurrence and supposed helical superstructure formed due to nitro groups interactions have induced the chirality of solid mDNB confirmed by the CD spectra record and ab initio quantum chemical calculations. The several times irradiation of mDNB crystal samples by the 980nm and 1550nm laser diode beams have revealed temporal fluctuations of radical anions concentration (EPR) and of NIR band intensities, as well as CD spectra changes. An autocatalytic reduction by NIR is supposed to be responsible for the observed fluctuations. The proposed conclusions were reinforced by the density functional (DFT) calculations of electronic properties (ionization energy, electron affinity, dipole moment, hyperpolarizability) of mDNB neutral and charged clusters formed along the hypothetical helix and by the calculation of crystal band structure. The UV–Vis–NIR absorption and CD spectra of mDNB molecular systems were computed at non-empirical all-electron level by DFT method within the correlation consistent 6-311G**(2d,2p) basis set and hybrid B3LYP density functional.