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Imidazole-based organic dyes for dye-sensitized solar cells: design, synthesis, and characterization Thompho Jason Rashamuse Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, South Africa E-mail: jasonr@mintek.co.za In this study, we designed and synthesized four novel imidazole-based organic molecules, Me3CM , OMe3CM , F3CM , and F4CM (1-3), for use in dye-sensitized solar cells through a five-step sequential reaction, as outlined in Scheme 1 (1-2). These molecules feature a carbazole core acting as an electron donor, with a carboxylic group attached to the 4-position of the imidazole unit, serving both as an electron acceptor and an anchoring group for binding to the TiO 2 surface. Each dye incorporates distinct substituents (a 3-methyl group, a 4-methoxy group, a 3-fluorine atom, and a 4-fluorine atom) at the 5-position of the imidazole’s phenyl ring, allowing for fine-tuning of the dyes’ optoelectronic properties. Additionally, two aromatic rings were introduced to link the central carbazole unit to the imidazole unit, enhancing the planarity of these organic dyes (3-4). Their structural properties were confirmed using a variety of analytical techniques, including 1D and 2D NMR, and FTIR. Following this, their photophysical and electrochemical properties were thoroughly investigated.
Cl
R
O
Cl
O
Cl
C
Cl
H 2 N
O
N
O
O
SOCl 2
O
2
N
5
Cl
N H
N
Cl
N
R
6
R
(i)
R
4
1
(ii)
(ii)
3
O
N
B
(iv)
O
7
R
R
O
O
R = 3-Me (Me3CM)
O
OH
3-OMe (OMe3CM) 3-F (F3CM) 4-F (F4CM)
N
N
N
N
N
N
(v)
8
Scheme 1: Reaction conditions: (i) Et 3 N, AcOEt, RT, 24 h; (ii) SOCl 2 , reflux, 16 h; (iii) ethyl isocyanoacetate, DBU, anhydrous THF, −78 0 C-RT, 48 h; (iv) XPhos Pd G3 (1%) K 2 CO 3 , anhydrous dioxane, H 2 O, 100 0 C; (v) NaOH, H 2 O, MeOH. Key words: Imidazole, dye-sensitized, Solar cells, carbazole unit, optoelectronic properties References 1. Rashamuse, Thompho J. et al. (2021). Molecules 26 (20), 6203.
2. Allen, J. D. W. et al. (2021). J. Mater. Chem. C, 9, 17419. 3. Pashaei, B., et al. (2016). Chem. Rev. 116(16), 9485. 4. Elsenety, M. M. (2024). Scientific Reports volume, 14, 26539
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© The Author(s), 2025
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