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

Paramagnetic species in the 1,3-dinitrobenzene (mDNB) crystal have been detected by EPR spectroscopy and the intervalence (conductivity) band at ∼10,400 cm−1 along the polar c axis, and the band at ∼7400 cm−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 980 nm and 1550 nm 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.

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► Unexpectedly, the circular dichroism spectra of 1,3-dinitrobenzene were recorded.
► NIR irradiations caused temporal fluctuations of EPR signals.
► Quantum chemical calculations confirmed the chirality of mDNB radical anion.
► Polarons concentration fluctuations suggests mDNB autocatalytic reduction by NIR.
► Polarons and helical packing seem to contribute to mDNB optical nonlinearity.