Regioisomeric Effects on the Electronic Features of Indenothiophene‐Bridged D–π‐A′–A DSSC Sensitizers

Abstract

Two D-π-A'-A regioisomers (A-IDT-D and D-IDT-A) featuring 4,4'-di-p-tolyl-4 H-indeno[1,2-b]-thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine-cyanoacrylic acid acceptor (A'-A) have been successfully synthesized and characterized as efficient sensitizers for the dye-sensitized solar cells (DSSCs). The different arrangements of the D and A'-A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A-IDT-D) or opposite (D-IDT-A) to the direction of intramolecular (donor-to-acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade-off between the molar extinction coefficient (ε) and the S0 →S1 transition energy. As a result, a superior ε value was observed for D-IDT-A, whereas a bathochromic shift in the absorption occurred in A-IDT-D. The larger ε value of D-IDT-A together with its more favorable energy level relative to TiO2 led to a higher power conversion efficiency of 7.41 % for the D-IDT-A-based DSSC, retaining approximately 95 % of the N719-based DSSC efficiency. This work manifests the clear structure-property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers.

Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics

“…MIDTP exhibits nearly coplanar conformations (Figure S5in SI). This structural feature is in line with previous observations that pyrimidine ring can relax the ortho-ortho steric interactions 23,30. As shown inFigure 3a, two MIDTP molecules align in a coplanar antiparallel fashion with respective molecular π-system parallel to the (1 3 -2) crystal plane.…”

“…The molecular design concept basically follows previous observations on D-π-A-A type dipolar molecules. 30 While the electron-donating di-p-tolylamine group (D) and electron-withdrawing pyrimidine-dicyanovinylene (A-A) attached to the phenylene ring 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 8 and C2 of an asymmetric IDT π-bridge, respectively, give molecules with relatively low-lying highest occupied molecular orbital (HOMO) energy levels that can contribute to a higher V oc . Buchwald-Hartwig aminations of di-p-tolylamine and IDT derivatives 1a-b (their syntheses are given in Scheme S1 in Supporting Information) afforded the donor-functionalized intermediates 2a-b, which were then subjected to selective Stille coupling reactions with 5-bromo-2-iodopyrimidine to yield their corresponding bromo The UV/Vis spectra of MIDTP and TIDTP in solution (CH 2 Cl 2 ) and vacuum-deposited thin films are shown in Figure 1a and the data are summarized in Table 1.…”

Novel Organic Dyes Featuring Spiro[dibenzo[3,4:6,7]cyclohepta[1,2-b]quinoxaline-10,9′-fluorene] (SDBQX) as a Rigid Moiety for Dye-Sensitized Solar Cells

“…The intense absorption bands in the near UV region could be assigned to the π−π* transition. 25 In the visible region, the absorption peaks corresponding to the intramolecular charge transfer (ICT) from the electron donor to the electron acceptor were observed at 484, 485, and 443 nm for FHD4, FHD5, and FHD6, respectively. Broader spectral coverages were observed for FHD4 and FHD5 containing electron-rich aromatic moieties, the furan and thiophene rings.…”

“…In solution absorption spectra, all of the three dyes exhibited two prominent peaks at around 440–490 and 350–400 nm. The intense absorption bands in the near UV region could be assigned to the π–π* transition . In the visible region, the absorption peaks corresponding to the intramolecular charge transfer (ICT) from the electron donor to the electron acceptor were observed at 484, 485, and 443 nm for FHD4 , FHD5 , and FHD6 , respectively.…”

Picolinic acid as an efficient tridentate anchoring group adsorbing at Lewis acid sites and Brønsted acid sites of the TiO2 surface in dye-sensitized solar cells

“…[7][8][9][10][11][12] Recently, Grätzel and coworkers prepared porphyrin dye SM315, which showed the highest PCE of 13% with a cobalt-based redox electrolyte. 13 In general, both the metal-complex sensitizers and organic sensitizers were oen designed as a typical donor-p-acceptor (D-p-A) framework, [14][15][16] due to their efficient intra-molecular charge transfer (ICT) properties. Researchers have developed many kinds of outstanding donors, such as triarylamine, diphenylamine, tetrahydroquinoline, phenothiazine, indoline and coumarin.…”