## 2 Materials and Methods
### General Procedure for Synthesis of Compounds (**6**-**9**)  
To a solution of the selected diazaphenothiazazine **(1**-**4**) (0.201 mg, 1 mmol) in dry DMF (10 mL), NaH (0.028 g, 1.2 mmol, 60% NaH in mineral oil was washed out with hexane) was added. The reaction mixture was stirred at room temperature for 1 h and then the linker \(\alpha\),\(\alpha^{\prime}\)-dichloro-\(m\)-xylene (0.5 mmol) was added, and the stirring was continued for 24 h. The progress of the reaction was monitored using TLC. The mixture was poured into water (15 mL), extracted with CHCl\({}_{3}\) (3 \(\times\) 10 mL), and dried using Na\({}_{2}\)SO\({}_{4}\). The obtained product was purified by column chromatography (aluminum oxide, CHCl\({}_{3}\)-Ethanol 10:1) to give the following:  
Figure 1: Structure of the investigated dimers with the \(m\)-xylene linker **(6**–**9**) and ludidine moiety **(6a**–**9a**). 1,3-bis((10\(H\)-dipyridylo [2,3-\(b\):\(J\):\(2^{\prime}\),3\({}^{\prime}\)-e][1,4]thiazin-10-yl)methyl)benzene (6) (214 mg, 85%), mp = 268-270 \({}^{\circ}\)C  
\({}^{1}\)H NMR (DMSO\({}_{\rm 46}\)) \(\delta\): 5.16 (s, 4H, 2 CH\({}_{\rm 2}\)), 6.69 (dd, \(J\) = 8.4 Hz, \(J\) = 1.2 Hz, 2H), 6.78 (dd, \(J\) = 7.2 Hz, \(J\) = 4.8 Hz, 2H), 6.84 (dd, \(J\) = 8.4 Hz, \(J\) = 4.8 Hz, 2H), 6.93 (s, 1H, H\({}_{\rm d\)-m-xylem), 7.18 (d, \(J\) = 7.2 Hz, 2H, H\({}_{\rm b\)-m-xylem), 7.31 (t, \(J\) = 7.2 Hz, 1H, H\({}_{\rm c\)-m-xylem), 7.37 (dd, \(J\) = 7.2 Hz, \(J\) = 1.2 Hz, 2H), 7.68 (dd, \(J\) = 4.8 Hz, \(J\) = 1.2 Hz, 2H), and 7.82 (dd, \(J\) = 4.8 Hz, \(J\) = 1.2 Hz, 2H). \({}^{13}\)C NMR: 47.58, 115.14, 119.10, 121.95, 122.56, 124.59, 125.45, 129.28, 135.11, 137.16, 137.92, 142.85, 143.17, 145.41, and 151.89. HR MS (EI) \(m/z\) for [C\({}_{\rm 28}\)H\({}_{\rm 21}\)N\({}_{\rm 6}\)S\({}_{\rm 2}\) + H], calc. 505.1264; found: 505.1283 (100%). 1,3-bis((10\(H\)-dipyridylo [3,2-\(b\):\(3^{\prime}\),4\({}^{\prime}\)-e][1,4]thiazin-10-yl)methyl)benzene (7) (209 mg, 83%), mp = 262-264 \({}^{\circ}\)C  
\({}^{1}\)H NMR (CDCl\({}_{3}\)) \(\delta\): 5.42 (s, 4H, 2 CH\({}_{2}\)), 6.90 (m, 2H), 7.17 (d, \(J\) = 6.0 Hz, 2H), 7.18 (d, \(J\) = 7.8 Hz, 2 H\({}_{\rm b\)-m-xylem), 7.21 (m, 2H), 7.27 (m, 1H, H\({}_{\rm c\)-m-xylem), 7.70 (s, 1H, H\({}_{\rm d\)-m-xylem), 8.05 (m, 2H), 8.14 (d, \(J\) = 6.0 Hz, 2H), and 8.19 (s, 2H). \({}^{13}\)C NMR: 48.02, 111.95, 120.20, 121.59, 125.52, 126.67, 128.23, 130.03, 134.95, 135.05, 140.91, 143.84, 147.14, 151.13, and 152.90. HR MS (EI) \(m/z\) for [C\({}_{\rm 28}\)H\({}_{\rm 21}\)N\({}_{\rm 6}\)S\({}_{\rm 2}\) + H], calc. 505.1264; found: 505.1283 (100%). 1,3-bis((10\(H\)-dipyridylo [3,4-\(b\):\(3^{\prime}\),4\({}^{\prime}\)-e][1,4]thiazin-10-yl)methyl)benzene (8) (216 mg, 86%), mp = 256-257 \({}^{\circ}\)C  
\({}^{1}\)H NMR (CDCl\({}_{3}\)) \(\delta\): 5.06 (s, 4H, 2 CH\({}_{2}\)), 6.35 (d, \(J\) = 5.7 Hz, 2H, 2 H\({}_{\rm b}\)\({}_{\rm 2}\) H\({}_{\rm 9}\)), 6.94 (s, 1H, H\({}_{\rm d\)-m-xylem), 6.97 (d, \(J\) = 4.8 Hz, 2H, 2 H\({}_{\rm 4}\)), 7.25 (d, \(J\) = 7.2 Hz, 2H, 2 H\({}_{\rm b\)-m-xylem), 7.45 (t, \(J\) = 7.2 Hz, 1H, H\({}_{\rm c\)-m-xylem), 7.70 (s, 2H, 2 H\({}_{\rm 1}\)), 7.76 (d, \(J\) = 5.7 Hz, 2H, 2 H\({}_{\rm 8}\)), 8.01 (s, 2H, 2 H\({}_{\rm 6}\)), and 8.10 (d, \(J\) = 4.8 Hz, 2H, 2 H\({}_{\rm 3}\)). \({}^{13}\)C NMR: 51.08 C\({}_{\rm 2}\), 109.41 C\({}_{\rm 9}\), 117.19 C\({}_{\rm 9a}\), 121.56 C\({}_{\rm 12}\), 123.48 C\({}_{\rm 1}\), 126. 06 C\({}_{\rm b}\), 130.79 C\({}_{\rm c}\), 133.35 C\({}_{\rm 10a}\), 134.46 C\({}_{\rm 13}\), 135.56 C\({}_{\rm 1}\), 137.22 C\({}_{\rm 4a}\), 143.44 C\({}_{\rm 15}\), 145.70 C\({}_{\rm 3}\), 147.14 C\({}_{\rm 8}\), and 151.47 C\({}_{\rm 5a}\). HR MS (EI) \(m/z\) for [C\({}_{\rm 28}\)H\({}_{\rm 21}\)N\({}_{\rm 6}\)S\({}_{\rm 2}\) + H], calc. 505.1264; found: 505.1229 (100%).