Alexander Konkin

In this study, two low-concentration solutions of 1,4,5,8-Naphthalene tetracarboxylic dianhydride (NTCDA) in two imidazolium-based ionic liquids (IL), EMIM-DCA and EMIM-Ac, at room temperature were mixed; after around ten days of storage, the formation of two variants of electron-withdrawing molecules of Naphthalene tetracarboxylic diimide NTCDI-R derivatives were detected. Their radical anions (RA) were registered by EPR via irradiating the resulting mixture of both solutions with visible or UV light. Chemical shift recording and precise concentration control of NTCDA in ionic liquid solutions were accomplished using 500 MHz and 700 MHz ¹H NMR. The formation of the NTCDA^•− upon light illumination was also confirmed by NMR, which showed paramagnetic broadening of the ¹H line due to the electron chemical exchange between NTCDA and NTCDA^•− after light-on and light-off modes. The time-dependent line broadening is in quantitative agreement with the corresponding EPR data for the light-on-/light-off-dependent concentration of NTCDA^•−. The putative structure of R in NTCDI-R was calculated by DFT. The possibility of using NTCDI-R^•− as a spin probe for studying molecular diffusion in high viscous ionic liquid is assessed.

Magnetic resonance, relaxation, and dynamic parameters of spin charge carriers photoinitiated in dual polymer composites formed by narrow-bandgap poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(bithiophene)] (F8T2), poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT), poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) copolymers modified with [6,6]-phenyl-C61-butanoic acid methyl ester (PC61BM) as photovoltaic spin subsystem and polyaniline salt doped with para-toluenesulfonic acid (PANI:TSA) as guest spin subsystem were comparatively studied by the direct Light-Induced Electron Paramagnetic Resonance (LEPR) spectroscopy in a wide photon energy and temperature range. Irradiation of dual polymer composite by the photons leads to the formation in its photovoltaic subsystem of polarons and methanofullerene radical anions whose concentration and dynamics are determined by the density and energy of the initiating light photons. A part of such polarons first filled high-energetic spin traps formed in the matrix due to its disordering. A crucial role of exchange interaction between different spin ensembles in the charge excitation, relaxation and transport in multispin narrow-bandgap composites was demonstrated. These processes were interpreted within the framework of hopping of polarons along copolymer chains of photovoltaic subsystems and their exchange interaction with neighboring spin ensembles. Such interaction was shown to facilitate the transfer of charges and inhibits their recombination in multispin dual polymer composites. The distribution of spin density over polymer chains in the dual polymer composites with the π-π-stacked architecture was analyzed in framework of the density functional theory (DFT). It confirmed the transfer of electron spin density between neighboring polymer chains that provokes formation more likely radical pairs in triplet state than singlet one and inhibits their fast geminate recombination. Spin interactions eliminate the selectivity of these systems to the photon energy, extends the range of optical photons they are absorbed and, therefore, increases their efficiency to converse the light energy. Handling electronic properties via intra- and inter-subsystem spin interactions in such multispin composites allows to create on their base a more efficient and functional electronic and spintronic elements.