Electron Spin Relaxation in x-Lithium Phthalocyanine

Abstract

Continuous-wave linewidths and spin susceptibilities, spin-spin relaxation rates (1/T2), and spin-lattice relaxation rates (1/T1) for two sources of x-LiPc were measured at 9.5 GHz between 15 and 298 K. Relaxation rates at 34 GHz were measured between 80 and 298 K. Room-temperature relaxation rates also were measured at 250 MHz, 1.9 GHz, and 2.76 GHz. The temperature dependences of linewidths and spin susceptibilities are characteristic of 1-D organic conductors. The ratio of populations of localized and delocalized electrons varies with sample preparation. For a single needle between 15 and about 200 K, 1/T2 is higher for the parallel orientation, but 1/T1 is higher for the perpendicular orientation, consistent with predictions based on dipolar interactions. Between about 60 and 150 K, which is the temperature regime in which spin susceptibility is changing rapidly with temperature, 1/T1 exhibits a non-monotonic dependence on temperature and is lower at 34 GHz than at 9.5 GHz. In other organic conductors, this dependence has been attributed to a bottleneck mechanism of relaxation. At higher temperatures, 1/T1 becomes less orientation-dependent. At room temperature, T1 increases rapidly between 250 MHz (3.0 micros) and 2.76 GHz (6.3 micros) and then shows less frequency dependence up to 34 GHz (9.8 micros). The relaxation rate near room temperature might have a substantial contribution from spin hopping perpendicular to the stacking axis of the molecules.

Digital EPR with an arbitrary waveform generator and direct detection at the carrier frequency

“…4) gave the absorption and dispersion components of the signal. The FWHM linewidth was 55 mG, which is consistent with measurements of CW lineshape and of T m by spin echo [32]. …”

Chirped ordered pulses for ultra-broadband ESR spectroscopy

“…x-LiPc is a microcrystalline powder of the P4mm space group in which electrons are delocalized over columnar lithium phthalocyanine stacks with a g-value of 2.002 26 ± 0.000 02. 64 At 294 K, the Fourier transform linewidth is 200 kHz, compared to the CW-ESR peak-to-peak linewidth of 4.5 μT. In relaxation, the T 1e was 4.5 μs and the phase memory time, Tm, was 2.3 μs, with a stretched exponential value x = 0.88.…”

Synthesis and Characterization of Lithium Hemiporphyrazines

“…For example, this method is very useful for the generation of the early transition metal ion porphyrins since these compounds often cannot be made by direct reaction of the free base in the presence of a source of the metal . In the phthalocyanines, lithiated macrocycles have been investigated as advanced materials for photosensitive and oximetric compounds …”