## 3 Experimental Sections  
Synthetic procedure: The synthesis of radical **4** was published previously [10].  
Instrumental analyses: Cyclic voltammetry (CV) measurements were performed on a Princeton Applied Research Potentiostat/Galvanostat 263A apparatus (Oak Ridge, TN, USA). The concentration of the benzotriazinyl radical **4** used was 1 mM in CH\({}_{2}\)Cl\({}_{2}\). A 0.1 M CH\({}_{2}\)Cl\({}_{2}\) solution of tetra-butylammonium tetrafluoroborate (\(n\)-Bu\({}_{4}\)BF\({}_{4}\)) was used as electrolyte. The electrolyte was dried for four days in the vacuum oven at 100 \({}^{\circ}\)C prior to the use. The reference electrode was Ag/AgCl and the scan rate was 50 mV/s. Ferrocene was used as an internal reference; the E\({}_{1/2}\)(ox) of ferrocene in this system was 0.352 V [26]. EPR spectra were recorded on a Bruker EMXplus X-band EPR spectrometer (Bruker, Billerica, MA, USA) at room temperature in dilute solution of CH\({}_{2}\)Cl\({}_{2}\). For the EPR spectrum, the microwave power was in the region 5-70 mW with modulation frequencies of 50 or 100 kHz and modulation amplitudes of 0.5-1.0 G\({}_{\text{pp}}\). Simulations of the solution spectrum was made using Winsim software [27]. X-ray data of **4** (CCDC 1474192) [28] were collected on an Oxford-Diffraction Supernova diffractometer, equipped with a CCD area detector utilizing Mo-K\(\alpha\) radiation (\(\lambda\) = 0.71073 A). A suitable crystal was attached to glass fibers using paratone-N oil and transferred to a goniostat where they were cooled for data collection. Unit cell dimensions were determined and refined by using 4562 (\(3.85\leq\theta\leq 27.68^{\circ}\)) reflections. Empirical absorption corrections (multi-scan based on symmetry-related measurements) were applied using CrysAlis RED software [29]. The structures were solved by direct method and refined on \(F^{2}\) using full-matrix least squares using SHELXJ97 [30; 31]. Software packages used: CrysAlis CCD [29] for data collection, CrysAlis RED [29] for cell refinement and data reduction, WINGX for geometric calculations [32] and Mercury 3.1 (CCDC, Cambridge, UK) [33]. The non-H atoms were treated anisotropically. The hydrogen atoms were placed in calculated, ideal positions and refined as riding on their respective carbon atoms. Magnetic properties were studied by using a Quantum Design SQUID MPMS\({}_{2}\) field-shielded magnetometer (Quantum Design Inc., San Diego, CA, USA). The DC (direct current) magnetic moment was measured for 43 mg sample of radical **4**, placed in gelatin capsules held by polyethylene straw. The magnetic susceptibilities were measured in the temperature range of 5-300 K in an applied field of 0.4 T. Data were collected in both warming and cooling modes with no significant differences in sample susceptibility.  
Crystal refinement data (4): C\({}_{23}\)H\({}_{24}\)N\({}_{3}\), \(M\) = 342.45, Orthorhombic, space group _Pna21_, \(a\) = 18.5886(10) A, \(b\) = 19.3115(9) A, \(c\) = 9.9148(6) A, \(\alpha\) = 90\({}^{\circ}\), \(\beta\) = 90\({}^{\circ}\), \(\gamma\) = 90\({}^{\circ}\), \(V\) = 35.59(2) A\({}^{3}\), \(Z\) = 8, T = 100(2) K, \(\rho_{\text{calcd}}\) = 1.278 g\(\cdot\)cm\({}^{-3}\), 2\(b_{\text{max}}\) = 25. Refinement of 470 parameters on 5357 independent reflections out of 12978 measured reflections (\(R_{\text{int}}\) = 0.0438) led to \(R_{1}\) = 0.04761 [I \(>\) 2\(\sigma\)(I)], \(wR_{2}\) = 0.1154 (all data), and \(S\) = 1.050 with the largest difference peak and hole of 0.227 and \(-\)0.176 \(\times\) 10\({}^{-3}\), respectively.