Date Published: April 25, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Yameng Ren, Jiao Liu, Aibin Zheng, Xiandui Dong, Peng Wang.
Continuous studies on the use of a polycyclic aromatic hydrocarbon as the central block of an organic photosensitizer have brought forth a new opportunity toward efficiency enhancement of dye‐sensitized solar cells (DSCs). In this paper, a nonacyclic aromatic hydrocarbon 9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacene, tethered with four 4‐hexylphenyl solubilizing groups is reported. The novel chromophore 9,9‐19‐19‐tetrakis(4‐hexylphenyl)‐9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacene is further functionalized with diarylamines and 4‐(7‐ethynylbenzo[c][1,2,5]thiadiazol‐4‐yl)benzoic acid to produce two donor–acceptor (D–A) organic photosensitizers, achieving good power conversion efficiencies up to 10.2% in DSCs.
Organic small molecules with polycyclic aromatic hydrocarbons (PAH) as the kernel segments are in general characteristic of high molar absorption coefficient, large luminescence yield, and excellent carrier mobility, triggering their extensive utilizations as light‐emitters, pigments, and optoelectronic materials.1 In recent studies, we and other groups have selected the highly emissive N‐annulated perylene (NP)2 to construct organic D–A dyes with desirable anti‐aggregation capacity,3, 4 achieving high power conversion efficiencies (PCEs) up of 13.0% without use of any coadsorbate.[[qv: 3h]] However, it should be perceived that NP is synthesized from 1‐nitroperylene, which can only be obtained from the nitration reaction of perylene at an 30% yield due to the remarkable formation of 3‐nitroperylene.[[qv: 2a,b]]
The synthetic routes to R1 and R2 are outlined in Scheme1. First, the key intermediate diethyl 2,5‐di(anthracen‐9‐yl)terephthalate (3) was prepared in good yield via the Suzuki‐Miyaura cross‐coupling of 2‐(anthracen‐9‐yl)‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (1) with diethyl 2,5‐dibromoterephthalate (2), by use of the highly active phosphine ligand 2‐(2′,6′‐dimethoxybiphenyl)dicyclohexylphosphine (Sphos).9 Thereafter, we implemented a carbonyl addition reaction of 3 using (4‐hexylphenyl)magnesium bromide to acquire a bis‐tertiary alcohol intermediate, which underwent intramolecular Friedel‐Crafts cyclization with the aid of solid acid catalyst Amberlyst 15 to afford 9,9‐19‐19‐tetrakis(4‐hexylphenyl)‐9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacene (4, THPDNP). Our DNP synthesis adopted the synthetic strategy for fluorene first proposed by Holmes and co‐workers10 Then, we performed bromination of 4 at room temperature to get a bromide, which was further cross‐coupled with bis(4‐(hexyloxy)phenyl)amine (DPA, 5)[[qv: 3a]] or bis(2′,4′‐bis(hexyloxy)‐[1,1′‐biphenyl]‐4‐yl)amine (DBPA, 6)11 via the Buchwald‐Hartwig cross‐coupling reaction to afford N,N‐bis(4‐(hexyloxy)phenyl)‐9,9,19,19‐tetrakis(4‐hexylphenyl)‐9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacen‐5‐amine (DPA‐THPDNP, 7) or N,N‐bis(2′,4′‐bis(hexyloxy)‐[1,1′‐biphenyl]‐4‐yl)‐9,9,19,19‐tetrakis(4‐hexylphenyl)‐9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacen‐5‐amine (DBPA‐THPDNP, 8). Subsequently, we performed mono‐bromination of 7 or 8 at room temperature to obtain a bromide, which was further cross‐coupled with butyl 4‐(7‐ethynylbenzo[c][1,2,5]thiadiazol‐4‐yl)benzoate[[qv: 3d]] using the Sonogashira reaction to produce an esterified dye precursor. Eventually, the esters were hydrolyzed with KOH as the catalyst, and the hydrolyzate were thoroughly acidified with diluted phosphoric acid aqueous solution to afford the desired dyes R1 and R2.
In summary, we have synthesized two metal‐free organic dyes characteristic of a PAH, 2H‐dinaphthopentacene. Dye R2 with a bulky auxiliary diarylamine electron‐donor has reached an excellent PCE of 10.2% under the AM1.5G full sunlight, owing to the effectively attenuated interfacial charge recombination and a significantly improved photovoltage. Our work should encourage further molecular engineering of anthracene‐based dyes and stimulate active explorations of polycyclic optoelectronic materials with anthracene as the basic building block in other fields.
Materials: LiTFSI, EMITFSI, DMFc, Fc, TBP, tris(dibenzylideneacetone)dipalladium (Pd2(dba)3), [1,1′‐bis(diphenylphosphino)ferrocene]dichloropalladium(II) (Pd(dppf)Cl2), palladium(II) acetate (Pd(OAc)2), 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (Sphos), tris(1,1‐dimethylethyl)phosphine (P(t‐Bu)3), N‐bromosuccinimide (NBS), (triisopropylsilyl)acetylene, sodium tert‐butoxide (NaOt‐Bu), potassium hydroxide (KOH), potassium phosphate (K3PO4), diethyl 2,5‐dibromoterephthalate, 4,4,4′,4′,5,5,5′,5′‐octamethyl‐2,2′‐bi(1,3,2‐dioxaborolane), and cesium carbonate (Cs2CO3) were purchased from Sigma‐Aldrich and used without further purification. Toluene, THF, dioxane, diisopropylamine, acetonitrile, ethanol, and chloroform were dried and distilled before use. (4‐Hexylphenyl)magnesium bromide19 was synthesized according to the literature procedure. Other chemicals were purchased and used without further purification. The synthetic routes to R1 and R2 are illustrated in Scheme 1 and preparation details are described as follows.
The authors declare no conflict of interest.