Intensified electrochemiluminescence and photoluminescence via supramolecular anion recognition interactions

Herein, intensified electrochemiluminescence (ECL) and photoluminescence (PL) via supramolecular anion recognition interactions are demonstrated. A bisindolylpyrrole derivative with a structure containing two indole groups and 2-hexyl-pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione, BIPPD, was designed and synthesized de novo to induce the enhanced ECL and PL emission based on hydrogen bonding interactions with the dihydrogen phosphate anion. Remarkably, the ECL quantum efficiency and PL quantum yield were discovered to increase up to 5.5-fold and 1.5-fold, respectively, via this anion coordination. Dopant PF6− was found not to form hydrogen bonds, while HSO4− doping does slightly with the receptor molecule. There was no enhancement in either ECL or PL in both scenarios, revealing great recognition selectivity of the synthesized BIPPD. Mechanistic studies via1H NMR, ECL, and PL spectra illustrated that the ECL processes varied in the presence and absence of H2PO4− doping, thus leading to the understanding of enhanced efficiency. The bisindolylpyrrole derivative will find applications in supramolecular and analytical chemistry via controlled hydrogen bonding interactions.


2-hexylpyrrole [3, 4-c]pyrrole-1,3-(2H,5H)-dione (2)
: To a suspension of compound 1 (2.75g, 17.7mmol) dissolved in 20 ml tetrahydrofuran (THF), was added a solution of N, N-dicyclohexylcarbodiimine (4.4 g, 21.3mmol) in 30 ml anhydrous THF at nitrogen atmosphere.After stirred and refluxed for 2 hours with a precipitate formed, the mixture was cooled to room temperature and filtered to remove the N, N'-dicyclohexylurea, which could be washed with more THF.The resulting THF solution was concentrated to 15 mL in vacuum, and hexylamine (1 g, 10 mmol) was added via a syringe at N 2 atmosphere.The mixture was subsequently stirred overnight at room temperature.The solvent was removed under vacuum to give a gummy material, and titration with dilute HCl gave a thick paste.An NaOH solution was added and stirred to neutralize the acid and then the solution was filtered to remove excess urea.The filtrate was neutralized with dilute HCl to give a white precipitate, which was filtered and dried giving 1 g 4-(hexylcarbamyl)pyrrole-3-carboxylic acid of white solid (42% yield).

ECL Efficiency Calculations
ECL quantum efficiency (Φ x ) was calculated relative to 1mM Ru(bpy) 3 (PF 6 ) 2 in MeCN in the annihilation pathway whose ECL efficiency was taken as 100%.This was done by taking the sum of the integration of both the ECL intensity and current values (versus time) for the compound against the standard, as described in the following equation S1:

Figure S9.
A small time window of a 300 s pulsing experiment using 1 mM BIPPD doped with 7 equivalents H 2 PO 4 -in anhydrous acetonitrile with 0.1 M TBAPF 6 as the supporting electrolyte with the applied potential being pulsed between -1.43 and 1.47 V vs. SCE at a frequency of 5 Hz.Table S1.The summary of the photophysical and ECL properties of BIPPD and BIPPD/H 2 PO 4 -system.
(S1)where x represented studied sample.Equation S1 is based on the principle of generated photos per electron.

Figure S8 .
Figure S8.The corresponding ECL-voltage curves of 1mM BIPPD doped with various equivalents of H 2 PO 4 -in anhydrous acetonitrile with 0.1 M TBAPF 6 as the supporting electrolyte at a scan rate of 0.1 V/s.Inset indicates the relative enhancement result of doping different equivalents of H 2 PO 4 -.

Figure S11 .
Figure S11.PL spectra of BIPPD in chlorobenzene at a concentration of 1 x10-5 mol/L (black) added with various equivalents of H 2 PO 4 -.The excited wavelength was at 390 nm.

Figure S12 .
Figure S12.UV-visible spectra of BIPPD (gray, dash line) film and its film added with 3 equivalents of H 2 PO 4 -(blue, dash line).

Figure S13 .
Figure S13.Side views of one conformer of BIPPD found within a unit cell of the determined crystal structure.

Figure S14 .
Figure S14.The X-ray crystal structure of BIPPD within the packing system in diferent views.

Figure S15 .
Figure S15.UV-visible binding studies of BIPPD in addition of TBA-H 2 PO 4 in chlorobenzene collected at 298 K. Experiments were performed with the same concentration of complex BIPPD.

Table S2 .
Crystal data and structure refinement for BIPPD.

Table S3 .
Atomic coordinates ( x 10^4) and equivalent isotropic displacement parameters (A^2 x 10^3) for BIPPD.U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.