Synthesis, Optoelectronic, and Transistor Properties of BODIPY- and Cyclopenta[c]thiophene-Containing π-Conjugated Copolymers

Abstract

Three new low-band-gap copolymers were synthesized by fusing dipyrromethene difluoroborane (BODIPY) as the acceptor (A) and thiophene-capped 5,5-bis­(hexyloxymethyl)-5,6-dihydro-4H-cyclopenta­[c]-thiophene (CPT) as the donor (D). The BODIPY unit was copolymerized through the ̀α′ positions (1 and 7 positions) in P1 and through the ̀β′ positions (2 and 6 positions) in P2 and P3. The additional acetylene unit between D and A in P3 enhanced the conjugation by minimizing the possible steric hindrance compared to that in P2, whereas P1 exhibited a more red-shifted absorption than P2 and P3 because of the more effective conjugaion through the ̀α′ positions of BODIPY. Importantly, the optical band gaps (E g opt) obtained from the onset of the absorption spectra are 1.28, 1.71, and 1.57 eV for P1, P2, and P3, respectively. P1 has the lowest band gap for any CPT-containing polymer. In the best transistor devices, a mobility improvement by 4 orders of magnitude from 3.22 × 10–6 cm2 V–1 s–1 for P2 to 0.01 cm2 V–1 s–1 for P1 was achieved. DFT calculations alongside measured charge-transport properties indicated that appreciable alterations in the optoelectronic properties of the polymers were achieved through minor changes in their structural features. The polymers were further characterized by thin-film X-ray diffraction, atomic force microscopy, and spectroelectrochemistry to investigate their material and electrochemical properties.

BODIPY‐Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin‐Film Transistors

“…Debnath et al synthesized three new low-band-gap copolymers P16-P18 ( Figure 16) by using BODIPY acceptor and thiophene-capped 5,5-bis(hexyloxymethyl)-5,6-dihydro-4H-cyclopenta[c]-thiophene (CPT) donor. [43] The CPT unit was connected through 3,5-positions and 2,6-positions of BODIPY in P16 and P17, respectively, whereas an additional acetylene spacer was used in P18. UV-vis-NIR region absorption spectra were recorded to examine the changes in the optical properties of the three polymers.…”

“…We should note that although fluorine is the typical substituent on the four-coordinate boron center (4,4-positions) and carbon is the typical atom at 8position, a number of different BODIPY building blocks have been realized in (opto)electronic applications with different substituents (e. g., cyano (À CN), acetylenyl (À C�CÀ ), and fluorene π-unit) at 4,4-positions and different atoms (e. g., nitrogen in aza-BODIPY) at 8-position. Although BODIPYs have very interesting structural/electronic characteristics with a great potential for further advancements in OPV and OTFT applications, a decade ago, they have rarely been studied and generally exhibited very low carrier mobilities (~10 À 5 -10 À 3 cm 2 V À 1 s À 1 ), [37][38][39][40][41][42][43][44][45] and poor photovoltaic performances (PCEs of only 1-2 %). [37,[46][47][48][49][50][51][52][53][54][55] Only very recent efforts in the past five years, including some work from our research groups, have advanced the performance of BODIPY-based materials in (opto) electronics reaching carrier mobilities of~0.01-0.2 cm 2 V À 1 s À 1 and PCEs of~6-9 %.…”

Selenium-Containing Fused Bicyclic Heterocycle Diselenolodiselenole: Field Effect Transistor Study and Structure–Property Relationship

“…Conjugated materials that experience considerable redox induced transformations in their absorptionproperties have verified utility in electrochromic devices 37,38. Spectroelectrochemistry of C4Se4 derivatives were studied to demonstrate their suitability as electrochromic materials by assessing their spectral variations in neutral and oxidized states 39,40.…”

Porphyrins and BODIPY as Building Blocks for Efficient Donor Materials in Bulk Heterojunction Solar Cells

“…Polymers with high hole mobilities for organic conjugated polymers have been described in the literature (Figure ). For example, polymers composed of BODIPY and thiophene units, Usta‐1 and Zade‐1, respectively exhibit hole mobilities of μ h = 0.17 cm 2 V −1 s −1 , and 0.01 cm 2 V −1 s −1 . Singh‐1 is a co‐polymer [BODIPY‐DPP], which exhibits ambipolar properties of hole ( μ h = 1.76 × 10 −2 cm 2 V −1 s −1 ) and electron mobility ( μ e = 1.12 × 10 −2 cm 2 V −1 s −1 ) …”