Development of Visible-Light Driven Cu(I) Complex Photosensitizers for Photocatalytic CO2 Reduction
Development of Visible-Light Driven Cu(I) Complex Photosensitizers for Photocatalytic CO2 Reduction
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DOI：
10.3389/fchem.2019.00418
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发表时间：
2019-06
影响因子：
5.5
通讯作者：
Hiroyuki Takeda;Yuki Monma;Haruki Sugiyama;H. Uekusa;O. Ishitani
中科院分区：
文献类型：
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作者：
Hiroyuki Takeda;Yuki Monma;Haruki Sugiyama;H. Uekusa;O. Ishitani
在异构型CuI(DMP)(DPEphos)+型络合物(DPEphos=[2-(二苯基膦)苯基]醚)中，通过在2，9-二甲基-1，10-菲咯啉(DMP)配体的4，7位引入不同的芳香取代基，合成了可见光响应型铜(I)络合物光敏剂。与含苯(Ph-)的类似物(ε=5,700Mε=5,700M−1 cm−1，λmax=388 nm)相比，在dmP配体上引入联苯基(BP-)提高了金属-配体电荷转移带在可见光区的摩尔消光系数(ε=7,500M−1 cm−1)。然而，引入4-R-Ph-基团(R=吸电子基团Nc-或NO2-)导致了带的红移，分别为λmax=390,400和401 nm。单晶X射线分析表明，由于Ph-基团的2，6-质子与DMP配体的5，6-质子之间的空间排斥作用，Ph-基团发生了扭曲。结果表明，4-R-Ph-基团的π共轭效应很弱，使得π*轨道的能量降低很小。然而，当4-R-ph-被5元杂环取代时，有较大的红移，导致MLCT吸收带的ε值增加。因此，取代2-苯并呋喃基团后，由于取代的ε配体上的−共轭扩展，在420 nm附近有一个肩峰(−=12,300Mπ1 cm DMP1)，并在可见光范围内产生了最大的可见光吸收。以Fe(Dmp)2(Ncs)2为催化剂，1，3-dimethyl-2-phenyl-2，3-dihydro-1H-benzo[d]imidazole为牺牲性还原剂，以所合成的CuI络合物为光敏剂，考察了其光催化还原CO的反应，结果表明，CuI络合物的CO生成量有所提高。
The visible-light responsive Cu(I)-complex photosensitizers were developed by introducing various aromatic substituents at the 4,7-positions of a 2,9-dimethyl-1,10-phenanthroline (dmp) ligand in a heteroleptic CuI(dmp)(DPEphos)+-type complexes (DPEphos = [2-(diphenylphosphino)phenyl]ether) for photocatalytic CO2 reduction. Introducing biphenyl groups (Bp-) on the dmp ligand enhanced the molar extinction coefficient (ε) of the metal-to-ligand charge transfer (MLCT) band in the visible region (ε = 7,500 M−1cm−1) compared to that of the phenyl (Ph-)-containing analog (ε = 5,700 M−1cm−1 at λmax = 388 nm). However, introducing 4-R-Ph- groups (R = the electron-withdrawing groups NC-, or NO2-) led to a red shift in the band to λmax = 390, 400, and 401 nm, respectively. Single-crystal X-ray analysis showed the Ph- groups were twisted because of the steric repulsion between the 2,6-protons of the Ph- groups and 5,6-protons of the dmp ligand. The result strongly indicated that the π-conjugation effect of the 4-R-Ph- groups is so weak that the lowering of the energy of the dmp π* orbitals is small. However, when 4-R-ph- was substituted by a 5-membered heterorings, there was a larger red shift, leading to an increase in the ε value of the MLCT absorption band. Thus, the substitution to 2-benzofuranyl- groups resulted in visible-light absorption up to 500 nm and a shoulder peak at around 420 nm (ε = 12,300 M−1cm−1) due to the expansion of π-conjugation over the substituted dmp ligand. The photocatalytic reaction for CO2 reduction was tested using the obtained CuI complexes as photosensitizers in the presence of a Fe(dmp)2(NCS)2 catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as a sacrificial reductant, which showed improved CO generation.