Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis.

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me 2 N-pbt), mononuclear [Pt(pbt)(R' 2 -pzH) 2 ]PF 6 (R' 2 -pzH = pzH 1a , 3,5-Me 2 pzH 1b , 3,5- i Pr 2 pzH 1c ) and diplatinum (Pt II -Pt II ) [Pt(pbt)(μ-R' 2 pz)] 2 (R' 2 -pz = pz 2a , 3,5-Me 2 pz 2b , 3,5- i Pr 2 pz 2c ) and [Pt(Me 2 N-pbt)(μ-pz)] 2 ( 3a ) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl 3 solution, to form the Pt III -Pt III complexes [Pt(R-pbt)(μ-pz)Cl] 2 (R = H 4a , NMe 2 5a ). Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a - c and 2a , b , which exhibit a typical 3 IL/ 3 MLCT emission, whereas in 2c the emission has some 3 MMLCT contribution. 3a displays unusual dual, fluorescence ( 1 ILCT or 1 MLCT/ 1 LC), and phosphorescence ( 3 ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3 O 2 and formation of 1 O 2 , whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a , the lowest electronic transitions (S 1 -S 3 ) have mixed characters (LMMCT/LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a ) and they are weakly emissive in rigid media. The 1 O 2 generation property of complex 3a is successfully used for the photooxidation of p -bromothioanisol showing its potential application toward photocatalysis.