Electropolymerization on ITO-Coated Glass Slides of a Series of π-Extended BODIPY Dyes with Redox-Active Meso-Substituents

Abstract

A series of meso-carbazole and meso-pyrene boron dipyrromethene(BDP) dyes have been synthesized using a two-step method. This simplified synthetic method did not require catalysts or oxidizing agents. Solution spectroscopic and electrochemical studies indicate that the HOMO and LUMO energies are dependent on the extent of π-conjugation associated with the pyrroles. Solution electrochemistry of the dyes in chloroform reveal film formation onto glassy carbon electrodes. Electrolysis of chloroform solutions of the dyes using indium tin oxide (ITO) glass slides as the working electrode show, using UV/vis spectroscopy, the formation of films. For two of the dyes, the BODIPY structure stays in tact upon electrolysis, exhibiting sharp absorption peaks on the ITO slides similar to that observed for the same dyes in solution.

Keywords: BODIPY; ITO; carbazole; electropolymerization.

Scheme 1

Electron collection at the anode of a DSSC.

Figure 1

Proposed structures of BDP1, BDP2, and BDP3.

Scheme 2

Synthesis of BDP1.

Scheme 3

Synthetic scheme for BDP2 and BDP3.

Figure 2

(A) Electronic spectra of BDP1 (red), BDP2 (blue), and BDP3 (violet) at room temperature in chloroform. (B) Emission spectra BDP1 (red), BDP2 (blue), and BDP3 (violet) excited at their respective absorption maxima in chloroform.

Figure 3

Cyclic voltammograms of mM chloroform solutions of BDP1 (A), BDP2 (B), and BDP3 (C) containing 0.1 M TBAPF₆ as supporting electrolyte. Glassy carbon working electrode, a platinum wire auxiliary, and non-aqueous Ag/Ag⁺ reference electrode. Scan rates of 100 mV/s. (D) overlay of cathodic region of (A–C) with blue (BDP1), red (BDP2), and green (BDP3).

Figure 4

Cyclic voltammetry of glassy carbon electrodes with adsorbed BDP1 (A), BDP2 (B), and BDP3 (C) in 0.1 M TBAPF₆ chloroform solutions, with a platinum wire auxiliary electrode and a nonaqueous Ag/Ag⁺ reference electrode. Fc/Fc⁺ redox couple measured in under the same conditions is overlayed. Scan rates of 100 mV/s.

Figure 5

Qualitative Jablonski diagram of the HOMO/LUMO energies determined from cyclic voltammograms of the adsorbed BDP dyes from Figure 3.

Scheme 4

Proposed structure of electropolymerized BDP1 on ITO glass slides.

Figure 6

(top) Cyclic voltammetry of mM chloroform solutions of BDP dyes with 0.1 M TBAPF₆ as supporting electrolyte, a square ITO glass slide as working electrode, platinum flag auxiliary electrode, and non-aqueous Ag/Ag⁺ reference electrode. (bottom) UV/vis spectra of ITO slides after electrolysis of the BDP dye solutions for 100 s at 1.5 V.

Figure 7

UV/vis spectra of ITO slides after electrolysis of chloroform solution of N-(4-formylphenyl) carbazole for 100 s at 2.0 V.

Figure 8

Structure of BDP4. (A) Cyclic voltammogram of a mM solution of BDP4 in 0.1 M TBAPF₆ in chloroform with a glassy carbon working electrode and a nonaqueous Ag/Ag⁺ reference electrode. (B) Cyclic voltammogram of coated glassy carbon electrode in 0.1 M TBAPF₆ with a nonaqueous Ag/Ag⁺ reference electrode overlayed with Fc/Fc⁺ redox couple.

Figure 9

Electronic spectrum of an ITO glass slide electro-coated with BDP4, blue line and the spectrum of BDP4 in chloroform solution, red line.

Figure 10

Overlayed normalized spectra of BDP1 (blue) and BDP4 (red) electropolymerized on ITO glass slides.