A 4-dimethylaminobenzoate-functionalized Ti₆-oxo cluster with a narrow band gap and enhanced photoelectrochemical activity: a combined experimental and computational study

Abstract

Organic donor-π-bridge-acceptor (D-π-A) dyes with arylamines as an electron donor have been widely used as photosensitizers for dye-sensitized solar cells (DSSCs). However, titanium-oxo clusters (TOCs) functionalized with this kind of D-π-A structured dye-molecule have rarely been explored. In the present study, the 4-dimethylaminobenzoate-functionalized titanium-oxo cluster [Ti(μ-O)(OiPr)(DMABA)]·2CHCH (DMABA = 4-dimethylaminobenzoate) was synthesized and structurally characterized by single-crystal X-ray diffraction. For comparison, two other Ti-oxo clusters, namely [Ti(μ-O)(OiPr)(AD)] (AD = 1-adamantanecarboxylate) and [Ti(μ-O)(μ-O)(μ-OiPr)(OiPr)(DMM)] (DMM = dimethylmalonate), were also studied. The DMABA-functionalized cluster exhibits a remarkably reduced band gap of ∼2.5 eV and much enhanced photocurrent response in comparison with the other two clusters. The electronic structures and electronic transitions of the clusters were studied by DFT and TDDFT calculations. The computational results suggest that the low-energy transitions of the DMABA-functionalized cluster have a substantial charge-transfer character arising from the DMABA → {Ti} cluster core ligand-to-core charge transfer (LCCT), along with the DMABA-based intra-ligand charge transfer (ILCT). These low-energy charge transfer transitions provide efficient electron injection pathways for photon-to-electron conversion.

Titanium‐Oxo Clusters with Bi‐ and Tridentate Organic Ligands: Gradual Evolution of the Structures from Small to Big

“…In most Ti 6 O 3 clusters, the COO groups are part of dicarboxylato ligands, viz. Ti 6 O 3 (O i Pr) 14 (O 2 C−X−CO 2 ) 2 (X= o ‐C 6 H 4 , [51] dimethylthio‐tetrathiofulvalene, [52] CH 2 , CH 2 CH 2 , [53] CMe 2 , [54] C=CHC 6 H 4 NR 2 [R=Ph, Et], [55] CH=CH, [56] C 6 H 4 −C 6 H 4 ; [57] Figure 5). The COO groups of the dicarboxylato ligands occupy the same positions as the monocarboxylato ligands in the type 1 Ti 3 O(OR) 8 (O 2 CR’) 2 clusters.…”

“… R=Et: R’=C 6 H 4 OPh [84] R= i Pr: R’=H, [29] Me, [85,86] Et, [87] Bu, [31] i Bu, [88] t Bu, [89] CHCl 2 , [24] cyclohex‐3‐enyl, [64] CH 2 Ph, [90] CH 2 ‐naphthyl, naphthyl, [91] C 6 H 4 Ph, C 6 H 4 t Bu, [92] anthracenyl, [62] adamantyl, [54] C 6 H 4 COO i Pr, [14b] C 6 H 4 NH 2 , [93] C 6 H 3 (X)NHMe (X=H, F, Cl), [93b] C 6 H 4 NMe 2 , [54] C 5 H 4 N, [25] C 5 H 3 N−CO 2 i Pr, [94] ferrocenyl [88,91] R=Bu: R’= t Bu [95] R= i Bu: R’= t Bu, [95] CMe 2 Et [83] R= t Bu: R’=Et, [31] CMe 2 Et, CH 2 t Bu [44] R=CH 2 t Bu: R’= i Pr, [14a] Ph [73] R=SiMe 3 : R’= t Bu, [95] CH 2 t Bu, CMe 2 Et [95a] …”

“…R= i Pr: R’=H, [29] Me, [85,86] Et, [87] Bu, [31] i Bu, [88] t Bu, [89] CHCl 2 , [24] cyclohex‐3‐enyl, [64] CH 2 Ph, [90] CH 2 ‐naphthyl, naphthyl, [91] C 6 H 4 Ph, C 6 H 4 t Bu, [92] anthracenyl, [62] adamantyl, [54] C 6 H 4 COO i Pr, [14b] C 6 H 4 NH 2 , [93] C 6 H 3 (X)NHMe (X=H, F, Cl), [93b] C 6 H 4 NMe 2 , [54] C 5 H 4 N, [25] C 5 H 3 N−CO 2 i Pr, [94] ferrocenyl [88,91] …”

Acid‐Controlled Synthesis of Carboxylate‐Stabilized Ti44‐Oxo Clusters: Scaling up Preparation, Exchangeable Protecting Ligands, and Photophysical Properties

“…[13,17] To date,a number of solution-based synthetica pproaches have been successfully developed for the preparation of various PTCs with different structures and interesting photochemicalproperties. [24][25][26][27][28][29][30][31][32][33] Generally,t he surface of manyl arge PTCs,i ncluding the well-known Ti 28 , [9] Ti 34 , [23] and Ti 42 , [27] are surrounded by alkoxide or mixed alkoxide and carboxylate ligands, and thereby suffer from poor air or hydrolytic stability.M oreover,m any of the reported PTCs are preparedb yu sing sophisticated protocols, [27,28,35] and therefore scale-up of thesep rotocols could easily cause morphological changes or structural damage of the target complex. In this context,i ti se ssential to develop a simple, easily scaled-up, and cost-effective synthetic approach for the large-scale productiono fh igh-nuclearity PTCs with attractive properties and potential commercial applications.…”

“…The geometrical and electronic structures of PTCs are highly tunable by simply varying the experimental conditions (e.g., stoichiometric ratio of reactants, solvents, reaction time/temperature, coordinating ligands) . To date, a number of solution‐based synthetic approaches have been successfully developed for the preparation of various PTCs with different structures and interesting photochemical properties . Generally, the surface of many large PTCs, including the well‐known Ti 28 , Ti 34 , and Ti 42 , are surrounded by alkoxide or mixed alkoxide and carboxylate ligands, and thereby suffer from poor air or hydrolytic stability.…”