Bridgehead Imine Substituted Cyclopentadithiophene Derivatives: An Effective Strategy for Band Gap Control in Donor–Acceptor Polymers

Abstract

Bridgehead imine substituted cyclopentadithiophene structural units offer the opportunity to modify the electronic properties, in particular, the HOMO–LUMO energy levels of donor–acceptor polymers with unprecedented precision. Utilizing a common synthetic pathway, copolymers with high average molecular weights, a variety of functionality, and properties suitable for solar cell incorporation can be generated. The fabrication of organic photovoltaic devices with these new materials is demonstrated.

Low band-gap polymers incorporating benzotriazole and 5,6-dialkoxy-benzothiadiazole as solution processable electrochromic materials

“…In the HOMO profile, the two carbons linking the thiophene and the acceptor unit is in the opposite phase while in the LUMO profile, these two carbons are in the same phase. Such patterns have been routinely observed in many D-A type conjugated systems [52][53][54][55], and this suggests that both the donor and the acceptor play an essential role in determining the energy levels. The energy levels of the HOMO and LUMO orbitals were computed for the monomer, dimer and oligomers, and the band gaps are plotted as a function of the inverse of the number of repeating monomer units [56,57].…”

Solution‐Processable Donor–Acceptor Polymers with Modular Electronic Properties and Very Narrow Bandgaps

“…of hexamethylditin (SnMe 3 ) 2 using Pd(PPh 3 ) 4 (10 mol%) in toluene at 80 °C affords the corresponding stannane ( 3 ) in 71% yield. The overall procedure is similar to that previously reported and full synthetic details can be found in the Supporting Information …”

“…We recently demonstrated that bridgehead imine‐substituted CPDT structural units can be used to systematically modify the highest occupied/lowest unoccupied molecular orbital (HOMO–LUMO) positions of DA copolymers by virtue of competing electronic effects between the cross‐conjugated imine aryl functionality and the polymer backbone (Figure , P1 ) . Here, we demonstrate that this structural motif, in combination with strong acceptors with progressively delocalized π‐systems, results in the capability to fine‐tune structural and electronic features, and overcome conjugation saturation behavior so as to achieve very narrow optical bandgaps ( E g opt < 0.5 eV).…”

Molecular weight and end capping effects on the optoelectronic properties of structurally related ‘heavy atom’ donor–acceptor polymers

“…[1][2][3][4][5][6][7][8] In addition to solid state structure, it is well known that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are critical for device performance. [9][10][11][12][13] Extensive monomer modication has been undertaken in order to tune energy levels and solid state structures, including: extending the conjugation of the polymer repeat unit, 14,15 single atom substitution in one or both of the donor and acceptor monomers, [16][17][18][19][20][21][22] and monomer side chain substitution. 23,24 Recently, single atom substitution has gained increasing attention because polymer properties may be predictably tuned through modular chemistry.…”