## 2 Materials and Methods
### Chemistry
Vis \(\lambda_{\max}\) (DXN): 729 nm, log \(\varepsilon\) = 5.15. Vis \(\lambda_{\max}\) (EtOH): 701 nm, log \(\varepsilon\) = 5.22. Vis \(\lambda_{\max}\) (MeOH): 695 nm, log \(\varepsilon\) = 4.45. Vis \(\lambda_{\max}\) (THF): 733 nm, log \(\varepsilon\) = 5.06. IR \(\upsilon_{\max}\) (KBr): 3052, 2912, 2853, 1729, 1549, 1450, 1304, 1253, 1177, 1087, 975 cm\({}^{-1}\); \({}^{1}\)H-NMR (600 MHz, CDCl\({}_{3}\)) \(\delta\): 9.28 (1H, d, \(J\) = 7.8 Hz, ArH), 7.77 (1H, s, ArH), 7.72 (1H, d, \(J\) = 8.4 Hz, ArH), 7.54 (1H, d, \(J\) = 7.8 Hz, ArH), 7.37 (1H, t, \(J\) = 7.5 Hz, ArH), 7.28 (1H, br s, ArH), 7.20 (1H, t, \(J\) = 7.5 Hz, ArH), 7.13 (1H, d, \(J\) = 8.4 Hz, ArH), 7.02 (1H, d, \(J\) = 9.0 Hz, ArH), 5.89 (1H, s, C=CH), 5.73 (1H, s, C=CH), 4.10-4.06 (4H, m, NCH\({}_{2}\)(CH\({}_{2}\))\({}_{4}\)CH\({}_{3}\)), 1.81 (4H, qt, NCH\({}_{2}\)CH\({}_{2}\)(CH\({}_{2}\))\({}_{3}\)H\({}_{3}\)), 1.53 (2H, qt, N(CH\({}_{2}\))\({}_{2}\)CH\({}_{2}\)(CH\({}_{2}\))\({}_{2}\)CH\({}_{3}\)), 1.45 (2H, qt, N(CH\({}_{2}\))\({}_{2}\)CH\({}_{2}\)(CH\({}_{2}\))\({}_{2}\)CH\({}_{3}\)), 1.42-1.32 (8H, m, N(CH\({}_{2}\))\({}_{3}\)(CH\({}_{2}\))\({}_{2}\)CH\({}_{3}\)), 0.94 (3H, \(t\) = 6.9 Hz, N(CH\({}_{2}\))\({}_{3}\)CH\({}_{3}\)), 0.91 (3H, \(t\) = 6.9 Hz, N(CH\({}_{2}\))\({}_{3}\)CH\({}_{3}\)) ppm; \({}^{13}\)C-NMR (150.91 MHz, CDCl\({}_{3}\)) \(\delta\): 175.52, 159.20, 149.78, 141.02, 139.19 (ArCH), 139.05, 136.67 (ArCH), 131.01 (ArCH), 128.53, 127.73 (ArCH), 126.98, 126.95 (ArCH), 123.83 (ArCH), 122.04 (ArCH), 116.06 (ArCH), 111.26 (ArCH), 93.13 (C=CH), 86.86, 85.41 (C=CH), 47.98 (NCH\({}_{2}\)), 46.17 (NCH\({}_{2}\)), 31.36 (CH\({}_{2}\)), 27.22 (CH\({}_{2}\)), 26.48 (CH\({}_{2}\)), 26.40 (CH\({}_{2}\)), 26.37 (CH\({}_{2}\)), 22.55 (CH\({}_{2}\)), 22.44 (CH\({}_{2}\)), 13.92 (CH\({}_{3}\)) ppm; HRESI-TOFMS _m/z_: 664.16035 [M]\({}^{+}\) (C\({}_{34}\)H\({}_{37}\)IN\({}_{2}\)O\({}_{2}\)S\({}^{+}\), calc. 664.16149). 1.2 Synthesis of 3-hexyl-2[(3-[(1-hexyl-6-iodoquinolin-2(1\(H\))-ylidene)methyl]-2-methoxy-4-oxocyclobut-2-en-1-ylidene)methyl]benzothazol-3-ium trifluoromethaneesulfonate (**11**)  
To a solution of squaraine cyanine dye **10** (0.800 g, 1.20 mmol) in anhydrous CH\({}_{2}\)Cl\({}_{2}\), stirred under N\({}_{2}\) atmosphere at r.t., was added an excess of CF\({}_{3}\)SO\({}_{3}\)CH\({}_{3}\) (0.395 mL, 3.60 mmol). After 28 h, the mixture was quenched with cold 5% aqueous NaHCO\({}_{3}\). The organic layer, after separation by decantation, was dried over anhydrous Na\({}_{2}\)SO\({}_{4}\) and the solvent removed under reduced pressure. Yield: 73%. Bright green crystals. M.p. 215-218 \({}^{\circ}\)C. Vis \(\lambda_{\max}\) (DMSO): 677 nm, log \(\varepsilon\) = 5.25. Vis \(\lambda_{\max}\) (ACN): 665 nm, log \(\varepsilon\) = 5.28. Vis \(\lambda_{\max}\) (ACT): 668 nm, log \(\varepsilon\) = 5.24. Vis \(\lambda_{\max}\) (DCM): 672 nm, log \(\varepsilon\) = 5.33. Vis \(\lambda_{\max}\) (DMF): 675 nm, log \(\varepsilon\) = 5.23. Vis \(\lambda_{\max}\) (DXN): 680 nm, log \(\varepsilon\) = 5.11. Vis \(\lambda_{\max}\) (EtOH): 668 nm, log \(\varepsilon\) = 5.27. Vis \(\lambda_{\max}\) (MeOH): 665 nm, log \(\varepsilon\) = 4.60. Vis \(\lambda_{\max}\) (THF): 671 nm, log \(\varepsilon\) = 5.26.