Supporting Information Supramolecularly Assisted Modulation of Optical Properties of BODIPY-Benzimidazole Conjugates Shrikant S. Thakare a, Goutam Chakraborty b, Parvathi Krishnakumar c, Alok K. Ray b, Dilip K. Maity c, Haridas Pal* d, Nagayan Sekar* a a Institute of Chemical Technology, Mumbai-400019, b Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai-400085, c Homi Bhabha National Institute, Mumbai-400094, d Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai-400085. Contents Sr. No. Tittle Page No. S1 Synthesis of dyes (Scheme 1) S2 S2 Characterization ( 1 H NMR, 13 C NMR and HRMS spectra) S3-S5 S3 Absorption and Emission spectra of the dyes in their aqueous S6 solutions S4 Fluorescence lifetime and anisotropy decay curves of the dye 2 S6-S7 S5 General binding equation for the cases of 1:1 complex S7-S8 S6 General binding equation for 1:2 stoichiometric complex S8-S9 S7 Oscillator strength and its relation to refractive index and transition dipole S9-S10 S1
S1. Synthesis: Both the dyes were synthesized according to the reported synthetic procedure. 1 The reaction steps invovoled are conceptually presented in Scheme S1. Synthesis of dye 1(2-H,6-benzimidazole-4,4-difluoro-1,3,5,7-tetramethyl-8-phenyl-4-bora- 3a,4a-diaza-s-indecene): To a solution of 2-formyl-BDP (0.28 mmol) in DMF (8 ml) was added ortho-phenylenediamine 0.29mmol) and p-tsoh (0.05 mmol). The reaction mass was allowed to stir at 80 o C for 4 h. The reaction was then at 80 C for 4 h. Reaction was monitored by TLC. After cooling to room temperature, the reaction was quenched by the addition of aqueous solution of NaHCO 3 (10%) and extracted with chloroform (2 X 20 ml). The organic layer was washed with water (2 X 30 ml) and brine solution (2 X 30 ml). The organic layer was dried over sodium sulphate and concentrated in vacuo. The crude compound was further purified by column chromatography using Hexane:EtOAc (70:30) system to obtain orange-yellow solid (91 mg) yield: 72 %. m.p.: 298 o C. 1H NMR: δ 1.38 (s, 3H), 1.5 (s, 3H), 2.52 (s, 3H), 2.65 (s, 3H), 6.31 (s, 1H), 7.17 (d, J = 5 Hz, 2H), 7.43 (m, J = 10 Hz, 3H), 7.59 (m, J = 10Hz, 4H), 12.31 (br s, 1H). 13C NMR: δ 12.9, 13.8, 14.6, 14.9, 122.9, 123.1, 128.2, 129.8, 129.9, 130.2, 132.3, 134.3, 140.0, 143.3, 145.2, 146.5, 153.3, 158.3. HRMS: calcd for C 26 H 23 BF 2 N 4 [M +1]+: 441.2063; found: 441.2033. Synthesis of dye 2 (2,6-di-benzimidazole-4,4-difluoro-1,3,5,7-tetramethyl-8-phenyl-4-bora- 3a,4a-diaza-s-indecene): 2,6-diformyl-BDP (0.18 mmol), o-phenylenediamine (0.37mmol) and p- TsOH (0.1 mmol) were mixed in DMF (8 ml). The reaction was then at 80 C for 4 h. After cooling to room temperature, the reaction solution was quenched by the addition of aqueous solution of NaHCO 3 (10%) and extracted with chloroform (2 20 ml). The organic layer was washed with water (2 X 30 ml) and brine solution (2 X 30 ml). It was then dried over sodium sulphate and concentrated in vacuo. The crude compound was further purified by column chromatography over silica gel using CHCl 3 /MeOH (99:1) to obtain the red solid (52 mg) yield: 35%, m.p.: 329 o C. 1H NMR: δ 1.58 (s, 6H), 2.70 (s, 6H), 7.47 (d, J = 5 Hz, 2H), 7.59 (d, J = 5Hz, 2H), 7.61 (d, J = 5Hz, 2H),7.62 (m, J = 10Hz, 3H). 13C NMR: δ 13.3, 14.1, 29.4, 31.1, 124.1, 126.8, 127.0, 128.2, 128.4, 130.0, 130.2, 131.3, 134.2, 142.0, 144.5, 146.1, 156.08. HRMS: calcd for C 33 H 27 BF 2 N 6 [M +1]+: 557.2437; found: 557.2479. S2
Scheme S1. Important reaction steps invovoled in the synthesis of dye 1 and dye 2. S2. Characterization: Figure S1. 1 H NMR spectra of Dye 1 S3
Figure S2. 13 C NMR spectrum of Dye 1 Figure S3. HRMS spectrum of Dye 1 S4
Figure S4. 1 H NMR spectrum of Dye 2 S5
Figure S5. 13 C NMR spectra of Dye 2 Figure S6. HRMS spectrum of Dye 2 S6
S3. Absorption and Emission spectra of the dyes in their aqueous solutions Figure S7. (A) Absorption and (B) fluorescence (λ exc 480 nm) spectra of dye 1 in its 3% methanolic aqueous solution at different concentrations. Figure S8. Absorption (A) and fluorescence (λ exc = 490 nm) (B) spectra of dye 2 in its 3% methanolic aqueous solution at different concentrations. S4. Fluorescence lifetime and anisotropy decay curves of the dye 2 S7
Figure S9. Fluorescence decay curves of dye 2 at (A) ph 2 and (B) ph 7 in the absence (1) and in presence (2) of 300 and 1200 µm CB7 host at their respective ph conditions. Figure S10. Fluorescence anisotropy decay curves for dye 2 at (A) ph 2 and (B) ph 7 in the absence (1) and in presence (2) of 300 and 1200 µm CB7 at respective ph conditions. Anisotropy decay for dye 2 at ph 7 could not be observed with confidence in the absence of CB7 host. S5. General binding equation for the cases of 1:1 complex Let us consider that the reactants A and B interact with each other to form only 1:1 complex as AB. Then the formation of these complexes can be presented as, K eq A+ B AB (1) For this system, the observed photophysical changes can be expressed as, X k A k AB k A k A A (2) In this equation it is assumed that contributions towards X obs from the species A and AB are proportional to their concentrations, and, k A, k AB are the respective proportionality constants. In terms of the initial concentration [A] 0 and the would be photophysical parameter is X, if [A] 0 was converted to AB, the proportionality constants k A and k AB can be expressed as, Thus, eq. (2) can be rewritten as, k X and k A X A X X A X A A A X A X X A A S8
XX X X X X X X1 X X (3) In this equation [A] eq is a variable and can be expressed in terms of [A] 0, [B] 0 and K eq. and the required equation can be derived as follows. Following the equilibrium reaction (1) we can write, K AB A B A A A B AB A A A B A A K A B K A A K A A A K A K B K A 1A A 0 A A K A K B 1K B K A 12K A B 2K A 2K B 4K A 2K A K A K B 1K B K A 12K A B 2K A 2K B 4K A B 2K A K eq A 0 K eqb 0 1K eq A 0 K eq B 0 1 2 4K 2 2 eq A 0 B 1 0 (4) 2K eq Thus, eq. 4 can be used to calculate [A] eq and then eq. 3 can be used to fit the changes in any photophysical property ΔX as a function of the [B] 0 concentration following nonlinear regression analysis 2. S6. General binding equation for 1:2 stoichiometric complex Considering that a dye D binds to a host B with stoichiometry of 1:2, the overall complexation equilibrium can be written as, Therefore, the effective equilibrium constant would be given as, (5) S9
K (6) For this system, if [D] 0 is the total D concentration used and if it is assumed that [D] 0 & [C] eq <<[B], the total host concentration used at any stage, then [C] eq can be expressed as, C K D B K D C B Or, Or, C D K B K B C D (7) For any photophysical properties of the dye, we can write, X k D k C (8) where k D and k C are the respective proportionality constants. If X is the value for D and X is the final value of the observed property on complete conversion of the dye to C, one can write, Thus, eq. 9 can be rewritten as, X k D and X k C k D (9) X X D D X C X D C D D X C D Or, Or, X X X X C D X X X X 10 Substituting eq. 7 into eq. 10 we get the required titration equation as, X X X X Eq. 11 in its simplified form can be written as, (11) S10
X X (12) Eq. 12 can be used to fit the changes in the photophysical properties X as a function of the [B] concentration following nonlinear regression analysis 3. S7. Oscillator strength and its relation to refractive index and transition dipole Oscillator strength (f) for the electronic transition for an absorption process is expressed as, 4,5. (13) where n is the refractive index of the medium and ε is the molar absorption coefficient at the absorption frequency ν. Following Einstein s theory of transition probabilities, 4,5 the above equation can be expanded to correlate f with the transition dipole moment integral M as, 4.39 109 0 2 h 2303 0 83 2 3h 2 (14) Or, 4.39 109 0 h 2303 0 83 2 3h 2 (15) where, N 0 is the Avogadro s number, h is the Plank s contestant, ν max is the wavenumber for the absorption maximum and c 0 is the velocity of light in the vacuum. Therefore, f value for the absorption process is directly related to the refractive index n and square of the transition dipole moment M. Following eq. (15) and considering that M value does not change much, as might be the cases for the neutral forms of the studied dyes, the oscillator strengths for their absorption process are expected to decrease on their encapsulation into the CB7 cavities, as the refractive index inside the CB7 cavity is reported to be significantly lower than that in bulk water. 6,7 For the cationic forms of the studied dyes, the above consideration of the changing n value cannot justify the increase in the oscillator strengths for their absorption process for the dyes encapsulation into the CB7 cavity, the change in the refractive index from going to bulk water to CB7 cavity cannot justify the results. In these cases, possibly the changes in the conformational structures of the dyes leading to the better planarity of the chromophoric moieties and hence an increase in the M value is responsible for the observed increase in the oscillator strength. References S11
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