Bi-diketopyrrolopyrrole (Bi-DPP) as a novel electron accepting compound in low band gap π-conjugated donor–acceptor copolymers/oligomers

Figures & data

Figure 1. Synthetic route of P1–P4. Reagents and conditions: (i) In case of the Suzuki cross coupling reaction: Pd(PPh₃)₄/potassium carbonate/Aliquat 336©/water/toluene/120 °C; in case of the Stille cross coupling reaction: Pd(PPh₃)₄/toluene/100 °C.

Figure 2. Normalized absorption spectra of the prepared copolymers P1–P4 and small molecule SM-Bi-DPP (a) in chloroform and (b) as thin film.

Figure 3. Cyclic voltammograms of the prepared copolymers and the small molecule: (a) Reduction and (b) oxidation.

Figure 4. Illustration of the energy level diagrams of the prepared copolymers as well as of the small molecule.

Scheme 1. Schematic representation of the synthesis of Bi-DPP. Reagents and conditions: (i) Ethyl acetate/lithium diisopropylamide/tetrahydrofuran/−78 °C; (ii) pyridinium chlorochromate/celite/dichloromethane/25 °C; (iii) ethyl 2-chloroacetate/potassium carbonate/sodium iodide/acetone/55 °C; (iv) ammonium acetate/acetic acid/120 °C; (v) thiophene-2-carbonitrile/Na-t-OC₅H₁₂/80 °C; (vi) 2-ethylhexyl iodide/potassium carbonate/dimethyl sulfoxide/100 °C; and (vii) bromine/chloroform/25 °C.

Table 1. Summarized molar mass and Ð values of the prepared copolymers.

Polymer	Mn (g/mol)	Mw (g/mol)	Ð
P1	9000	19,200	2.1
P2	10,800	33,700	3.1
P3	15,500	64,300	4.2
P4	31,400	138,500	4.4

Scheme 2. Schematic representation of the synthesis of SM-Bi-DPP. Reagents and conditions: (i) Benzofuran-2-ylboronic acid/potassium carbonate/Pd₂(dba)₃/((t-butyl)₃PH)BF₄/tetrahydrofuran/water/25 °C.

Table 2. Summarized optical and electrochemical properties of the prepared copolymers and the small molecule.

Polymer	λmax (nm) solution	λmax (nm) film	λedge (nm) film	Eg,opt. (eV)	HOMOel. (eV)	LUMOel. (eV)	Eg,el. (eV)
P1	585, 379	600, 382	693	1.79	−5.34	−3.58	1.76
P2	590, 366	600, 372	691	1.79	−5.34	−3.59	1.75
P3	594, 368	603, 368	691	1.79	−5.28	−3.55	1.73
P4	639, 414	632, 404	742	1.67	−5.07	−3.55	1.52
SM-Bi-DPP	605	616	690	1.79	−5.30	−3.49	1.81