All reagents needed were used as purchased (Aldrich), without further purification. MWCNT were provided by Prof. Mazzocchia of Politecnico di Milano, Italy. Nuclear Magnetic Resonance (NMR) spectra were recorded on a Bruker AC-E Series 300 spectrometer. The UV-vis absorbance spectra were recorded with a Beckmann DU

650 spectrometer. IR spectra were recorded with a PerkinElmer mod. 297 spectrometer.

Fluorescence spectra were acquired with a JASCO FP-777W spectrofluorimeter; the slit widths were fixed at 3 and 5 nm for the excitation and the emission, respectively, the excitation wavelength was fixed at 337 nm and emission interval was fixed at 360 - 450 nm. SEM investigations were performed by using a Philips XL30 equipped with an Energy Dispersive X-ray device. Samples were supported on the stubs by carbon paint. The accelerating voltage ranged between 20 and 25 kV. Thermogravimetric analyses were performed by a Q5000 IR apparatus (TA Instruments) under a nitrogen flow of 25 cm³∙min⁻¹ for the sample and 10 cm³∙min⁻¹ for the balance. The weight of each sample was ca. 10 mg. The measurements were carried out by heating the sample from room temperature to 900˚C at a rate of 10˚C∙min⁻¹.

Micro-Raman spectra were carried out at room temperature by a Bruker-Senterra micro-Raman equipped with a 532 nm diode laser excitation with 20mW power. Measurements were carried out in the range 3500 - 1000 cm⁻¹ with spectral resolution from 9 to 15 cm⁻¹. The dispersions were analysed after removing of the solvent.

The proper alkyl alcohol (10 g) was dissolved in Et₂O (100 mL), under inert atmosphere (Ar), stirred for a few minutes in an ice bath, and a suitable amount of POCl₃ was added. After two days the crude compound was added dropwise, at 0˚C, to a solution of β-naphthol and NaH (molar ratio 1:1) in Et₂O (500 mL) under inert atmosphere (Ar). The mixture was stirred for 1 day, and subsequently extracted with water, then with NaOH (0.2 N) and finally with a saturated NaCl solution. The organic phase was dried on MgSO₄, filtered and evaporated in vacuum. The residue was purified by chromatography on silica gel (eluents: petroleum ether 100%, ethyl acetate 100%).

Compound 1a: red oil, yield 58%; ¹H NMR (300 MHz, CDCl₃, δ): 7.80 (m, 3H, Ar H), 7.68 (m, 1H, Ar H), 7.42 (m, 3H, Ar H), 4.16 (m, 4H, O-CH₂), 1.68 (m, CH₂, 4H), 1.27 (m, 20H, CH₂), 0.88 (t, J = 6.4 Hz, 6H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 148.87, 134.29, 131.26, 130.16, 128.07, 127.05, 125.79, 120.49, 116.79, 69.10, 32.12, 30.68, 29.53, 25.80, 23.00, 14.56 ppm. IR (oil): ν = 1286 (s, P=O), 1246 (w, P-O-Ar), 1022 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₂₆H₄₁O₄P: C, 69.62; H, 9.21; P, 6.90. Found: C, 69.66; H, 9.19; P, 6.93.

Compound 1b: red oil, yield 78%; ¹H NMR (300 MHz, CDCl₃, δ): 7.49 (m, 3H, Ar H), 7.44 (m, 1H, Ar H), 7.37 (m, 3H, Ar H), 4.17 (m, 4H, O-CH₂), 1.70 (quintet, J = 6.6 Hz, 4H, CH₂), 1.31 (m, 28H, CH₂), 0.88 (t, J = 6.6 Hz, 6H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 146.99, 132.41, 129.39, 128.30, 126.20, 125.19, 123.93, 118.62, 114.93, 67.25, 30.40, 28.82, 28.02, 27.82, 27.63, 23.94, 21.20, 12.64 ppm. IR (oil): ν = 1288 (s, P=O), 1245 (s, O-Ar), 1020 (s, P-O-CH₂) cm⁻¹. Anal calcd. for C₃₀H₄₉O₄P:C, 71.40; H, 9.79; P, 6.14. Found: C, 71.45; H, 9.81; P, 6.12.

Compound 1c: red oil, yield 74%; ¹H NMR (300 MHz, CDCl₃, δ): 7.81 (m, 3H, Ar H), 7.69 (m, 1H, Ar H), 7.38 (m, 3H, Ar H), 4.18 (m, 4H, O-CH₂), 1.70 (quintet, J = 6.7 Hz, 4H, CH₂), 1.25 (m, 36H, CH₂), 0.89 (t, J = 6.4 Hz, 6H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 151.18, 139.09, 133.86, 129.71, 127.63, 127.46, 126.61, 125.36, 120.06, 116.30, 68.68, 31.87, 30.26, 29.58, 29.30, 29.06, 25.37, 22.64, 14.06 ppm. IR (oil): ν = 1287 (s, P=O), 1246 (s, P-O-Ar) 1052 (s, P-O-CH₂) cm⁻¹. Anal. calcd.for C₃₄H₅₇O₄P:C, 72.82; H, 10.24; P, 5.42. Found: C, 72.79; H, 10.27; P, 5.41.

Compound 1d: red oil, yield 71%; ¹H NMR (300 MHz, CDCl₃, δ): 7.81 (m, 3H, Ar H), 7.69 (m, 1H, Ar H), 7.42 (m, 3 H, Ar H), 4.18 (m, 4H, O-CH₂), 1.65 (quintet, J = 6.8 Hz, 4H, CH₂), 1.29 (m, 44H, CH₂), 0.80 (t, J = 6.4 Hz, 6H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 152.30, 130.85, 129.75, 127.67, 127.50, 126.65, 125.40, 120.02, 116.41, 68.71, 31.91, 30.29, 30.19, 29.64, 29.53, 29.34, 29.09, 25.40, 22.66, 14.09 ppm. IR (oil): ν = 1281 (s, P=O), 1246 (s, P-O-Ar), 1019 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₃₈H₆₅O₄P: C, 73.98; H, 10.62; P, 5.02. Found: C, 73.95; H, 10.65; P, 5.00.

Compound 1e: red oil, yield 94%; ¹H NMR (300 MHz, CDCl₃, δ): 7.81 (m, 3H, ArH), 7.69 (m, 1H, ArH), 7.45 (m, 3H, ArH), 4.16 (m, 4H, O-CH₂), 1.70 (m, 4H, CH₂), 1.27 (m, 52H, CH₂), 0.89 (t, J = 5.41 Hz, 6H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 150.85, 130.86, 129.70, 127.62, 127.45, 126.60, 125.34, 119.97, 116.29, 68.66, 31.86, 30.25, 29.62, 29.50, 29.30, 29.05, 25.36, 22.63, 14.04 ppm. IR (oil): ν = 1280 (w, P=O), 1247 (s, P-O-Ar), 1016 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₄₂H₇₃O₄P:C, 74.96; H, 10.93; P, 4.60. Found: C, 74.99; H, 10.91; P, 4.62.

Compound 2a: red oil, yield 50%; ¹H NMR (300 MHz, CDCl₃, δ): 7.80 (m, 8H, Ar H), 7.42 (m, 6H, Ar H), 4.32 (m, 2H, O-CH₂), 1.72 (quintet, J = 6.9 Hz, 2H, CH₂), 1.29 (m, 10H, CH₂), 0.86 (t, J = 7.2 Hz, 3H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 148.25, 133.82, 131.02, 129.91, 127.68, 127.54, 126.75, 125.59, 119.97, 116.68, 69.72, 31.64, 30.23, 29.05, 25.32, 22.55, 14.14 ppm. IR

(oil): ν = 1293 (s, P=O), 1241 (s, P-O-Ar), 1039 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₂₈H₃₁O₄P: C, 72.71; H, 6.76; P, 6.70. Found: C, 72.68; H, 6.78; P, 6.72.

Compound 2b: red oil, yield 73%; ¹H NMR (300 MHz, CDCl₃, δ): 7.82 (m, 8H, Ar H), 7.46 (m, 6H, Ar H), 4.35 (m, 2H, O-CH₂), 1.74 (quintet, J = 6.9 Hz, 2H, CH₂), 1.25 (m, 14H, CH₂), 0.90 (t, J = 6.4 Hz, 3H, CH₃); ¹³C NMR (300 MHz, CDCl₃, δ): 148.23, 133.79, 130.99, 129.87, 127.64, 126.71, 125.54, 119.95, 116.64, 69.67, 31.78, 30.20, 29.37, 29.19, 28.96, 25.97, 22.60, 14.03; IR (oil): ν = 1293 (s, P=O), 1241 (s, P-O-Ar), 1020 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₃₀H₃₅O₄P. C, 73.45; H, 7.19; P, 6.31. Found: C, 73.42; H, 7.22; P, 6.33.

Compound 2c: red oil, yield 43%; ¹H NMR (300 MHz, CDCl_3, δ): 7.80 (m, 8H, Ar H), 7.46 (m, 6H, Ar H), 4.34 (m, 2H, O-CH₂), 1.73 (quintet, J = 6.9 Hz, 2H, CH₂), 1.26 (m, 18H, CH₂), 0.90 (t, J = 5.3 Hz, 3H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 148.21, 133.78, 130.98, 129.87, 127.64, 126.70, 126.20, 125.55, 119.93, 116.64, 69.68, 31.83, 30.19, 29.53, 29.42, 29.36, 29.26, 28.96, 25.29, 22.60, 14.03 ppm. IR (oil): ν = 1293 (s, P=O), 1241(s, P-O-Ar), 1020 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₃₂H₃₉O₄P:C, 74.11; H, 7.58; P, 5.97. Found: C, 74.14; H, 7.62; P, 5.95.

Compound 2d: red oil, yield 55%; ¹H NMR (300 MHz, CDCl₃, δ): 7.80 (m, 8H, Ar H), 7.45 (m, 6H, Ar H), 4.33 (m, 2H, O-CH₂), 1.73 (quintet, J = 6.8 Hz, 2H, CH₂), 1.26 (m, 22H, CH₂), 0.89 (t, J = 5.9 Hz, 3H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 148.20, 133.77, 130.98, 129.87, 129.36, 127.64, 126.70, 125.55, 119.92, 116.64, 69.69, 31.84, 30.19, 29.57, 29.42, 29.28, 28.96, 25.28, 22.61, 14.10 ppm. IR (oil): ν = 1280 (s, P=O), 1243 (s, P-O-Ar), 1036 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₃₄H₄₃O₄P: C, 74.70; H, 7.93; P, 5.67. Found: C, 74.73; H, 7.91; P, 5.68.

Compound 2e: red oil, yield 48%; ¹H NMR (300 MHz, CDCl₃), δ): 7.42 (m, 8H, Ar H), 7.30 (m, 6H, Ar H), 4.32 (m, 2H, O-CH₂), 1.71 (quintet, J = 7.2 Hz, 2H, CH₂), 1.25 (m, 26H, CH₂), 0.87 (t, J = 6.6 Hz, 3H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃, δ): 145.73, 131.31, 128.52, 127.42, 125.19, 124.26, 123.11, 117.48, 114.18, 67.24, 29.39, 28.39, 27.73, 27.16, 26.98, 26.83, 26.51, 22.83, 20.16, 11.59 ppm. IR (oil): ν = 1299 (w, P=O), 1243 (w, P-O-Ar), 1020 (s, P-O-CH₂) cm⁻¹. Anal. calcd. for C₃₆H₄₇O₄P: C, 75.23; H, 8.24; P, 5.39. Found: C, 75.20; H, 8.27; P, 5.41.

Varying weighted amounts of MWCNT (between 1 × 10⁻⁴ and 8 × 10⁻⁴ g) were dispersed, for 30 minutes, by sonication in ca. 20 mL of CHCl₃ at an ultrasound power of 200 W and a temperature of 25˚C. A CHCl₃ solution (100 μL) of phosphate ester additive (0.1 M) was added to the MWCNT dispersions and the resulting systems were again sonicated for further 30 minutes under the same condition previously reported. The final volume of the obtained dispersions was 100 mL and the concentration of additive was 1 × 10^{−4 M.}

The synthesis of phosphate esters, involved in the formation of hybrids was carried out in the first by reaction between the alcohols, with chain length variable, and a suitable amount of POCl₃ and then crude compounds were reacted with the aromatic β-naphthol to obtained the compounds 1,2 a-e (Figure 2). Phosphate esters obtained were used in the formation of hybrids in a concentration range lower than that of micellization [21]. The formation of hybrids was carried out by adding 1 × 10⁻⁴ M of phosphate ester to a “dispersion”, at increasing amount, of pristine MWCNTs in CHCl₃. Successful functionalization was immediately visible, resulting in the formation of dark dispersions, where the change of color intensity provides a qualitative indication of the amount of nanotube present (Figure 3(a)). By contrast, MWCNTs precipitated out almost completely, after the same sonication protocol, when the phosphate ester was not added (Figure 3(b)). Considering that the stability of a dispersion is the result of a delicate balance of attractive and repulsive forces, it seemed that the improved MWCNT dispersibility is due to the interaction between aryl groups and the CNT surface, [12] because chain phosphate esters, which do not include any conjugated

structure, were weakly adsorbed on the CNT surfaces and gave rise to a slight increase in the CNT dispersibility in chloroform. The dispersions were stable from one (2a-e) to at least three (1a-e) weeks. Dispersion stability was assessed by UV-vis analysis. Different dispersions, at varying amounts of MWCNTs (3 × 10⁻⁶, 5 × 10⁻⁶ and 8 × 10⁻⁶ g/mL respectively) and fixed concentration of 1 (1 × 10^{−4 M}) were monitored for three weeks. The change in absorbance, at 272 nm (see below) as a function of time was observed. Indeed, the values of absorbance of MWCNTs pristine and phosphate esters 1a-e were 0.12 and ca. 0.5, respectively, in contrast all hybrids showed absorbance values higher than 1.1 at time 0; this denotes that there was an interaction between phosphate esters and MWCNTs and so the hybrids formation. In Figure 4(a) is shown the plot of the absorbance as a function of time for dispersion with a MWCNT concentration of 5 × 10⁻⁶ g/mL. In this case we observed a curve that reach a plateau after ca. three weeks and the ab- sorbance values recorded were ca. 1.3. After three weeks, a slight precipitation of MWCNTs was, also, observed. The same considerations can be made for the dispersion with a MWCNT concentration of 3 × 10⁻⁶ g/mL. In

Figure 4(b) is shown the plot of the absorbance as a function of time for the dispersion with MWCNT concentration of 8 × 10⁻⁶ g/mL. In this case we observed a different behavior; in fact, the absorbance value (1.42) initially decreases in a linear manner until at a value of ca. 1.3 after 300 hours, successively, a slight precipitation was observed too. Experimental data collected, showed that dispersions of hybrids with phosphate esters 2a-e were less stable. The greater stability of the hybrids dispersions with phosphate esters 1a-e than with phosphate esters 2a-e can be explained admitting that compounds 1a-e, with two alkyl chains, wrap the MWCNT surface more efficiently than the stiff compounds 2a-e, in spit of their higher π surface. Probably, because the absorbance variations are similar for the two ester classes it is possible to deduce that only one aromatic ring interacts with MWCNT surface, so the different stability is determined by alkyl chains length.