Supplementary Information

Cavity Size Effect on ICT-Dual Emission of p- (N,N-Dimethylamino)-2-styrylquinoline: Complexation with Cyclodextrin Derivatives

SUBRAMANIAN ANNALAKSHMI and KASI PITCHUMANI*

School of Chemistry, Madurai Kamaraj University, Madurai-625 021, India

Details of experimental methods:

Synthesis of p- (N,N-Dimethylamino)-2-styrylquinoline

A solution of quinaldine (4.2 g, 0.029 mol), benzaldehyde (3.5 g, 0.033 mol) and acetic anhydride (2.0 g, 0.015 mol) was heated at 160C for 16 h in a 100 mL round bottomed flask fitted with a reflux condenser. The hot solution was poured into 20 mL of 10% sodium hydroxide solution. After the oil congealed, the solid was removed by filtration, washed with water then with 3 mL of ice cold ethanol and dried at 60C. The yield of crude 2-styrylquinoline was 4.2 g (0.018 mol) (m. pt. 98-99C). Recrystallization from a mixture of benzene (8 mL) and ligroin (10 mL) gave 3.5g (0.015mol) of the product. m. pt. 129-130C, 165-166C (lit.24 130, 170C) for 4-methyl and 4-N,N-dimethyl substituted styryl- quinolines respectively.

1H-NMR of p- (N,N-Dimethylamino)-2-styrylquinoline ( in ppm, CDCl3, 300 MHz): 7.15-7.68 (m, 6H), 6.67-6.81 (dd , 2H), 6.58-6.62 (m, 4H), 2.90 (s, 6H).

Preparation of stock solution for emission studies

Stock solution of 4-substituted 2-SQ (1 x 10-3 M) was prepared by dissolving a known amount of the compound in acetonitrile and then by sonication. Aliquot (0.1 mL) of the stock solution was transferred into 10 mL volumetric flask and then the various cyclodextrin concentration were added from the CD (1x 10-3 M) stock solution in water-freshly prepared and diuted to 10 mL with water then stirred for 6 h. Absorption and emission spectra were recorded. The slit width for the excitation and emission monochromators were 5 nm with a scan speed of 240 nm/min.

Calculation of equilibrium constants22

By absorption method, the equilibrium constants (1:1 host-guest complexation) were also calculated for 2-StQ-NMe2in presence of all the cyclodextrins using the following equation 1.

---1

The fluorescence enhancement F/F0 measured as a function of host concentration can be used to obtain the association constant for the host-guest inclusion process. In the case of 1:1, host:guest inclusion, a single equilibrium is involved, with association constant K:

S = Substrate

In this case, the dependence of F/F0 on added host concentration, [CD]0, is given by the following equation 2.

---2

Where F/F0 is the maximum enhancement, when all guests are complexed within a host. If only 1:1 complexes are formed, then the double-reciprocal plot of 1/(F/F0-1) verses 1/[CD]0 will be linear; a non-linear double reciprocal plot indicates the presence of higher-order inclusion complexes.

Considering the 1:2 complexation of substrate with two molecules of cyclodextrin, the binding constant was calculated by the following stepwise mechanism.

These two equilibria are described by the equilibrium constants K1 and K2:

with the overall equilibrium constant for 2:1 complexation equal to the product K1 and K2. The dependence of F/F0 on [CD]0 for this complexation mechanism is given by the following eqn.3

---3

Table 3. Binding Constant for p- (N, N-dimethylamino-2-styrylquinoline in presence of various cyclodextrins

Medium / Binding Constant (UV) K (M-1) / Binding Constant
(emission) K (M-1)
at 543 nm (LE band) / Binding Constant
(emission) K (M-1)
at 587 nm (ICT band)
-CD / 1119 / 1913 / 6737
-CD / 1089 / 1897 / 2014
-CD / 5272 / 2717 / 7033
HP--CD / 2924 / 2707 / 1057
HP--CD / 3151 / 4527 / 3755
HP--CD / 3207 / 6584 / 3202
DM--CD / 3639 / 7325 / 5147
Trimethyl--CD / 5272 / 3508 / 4736

Molecular modeling studies:

Molecular mechanics calculations23 were carried out using Insight II/ Discover program for all the complexes of CD/2-StQ-NMe2 in IRIX system. Calculations are done in a vacuum and structures are minimized using a CVFF force filed and the RMS derivative 0.0001 is achieved in each case.

Figure 4a. Mode of inclusion of 2-StQ-NMe2 in presence of -cyclodextrin

Figure 4b. Mode of inclusion of 2-StQ-NMe2 in presence of - -cyclodextrin

Figure 4c. Mode of inclusion of 2-StQ-NMe2 in presence of -cyclodextrin

Figure 5. Job’s plot of 2-StQ-NMe2 in presence of ,  and -cyclodextrins.