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Site-specific intrastrand and interstrand cross-links of BBR3464. Bending, protein recognition and nucleotide excision repair

Site-specific intrastrand and interstrand cross-links of BBR3464. Bending, protein recognition and nucleotide excision repair

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enhancement on

stilbazole complexation occurs in (29), and of the tetrahedral ZnII complexes (30)–(32), only the

chloride and trifluoroacetate show increases over the free ligand.81 The CT values estimated

from SC studies for (29) and (30) differ greatly from the corresponding EFISHG 1340 values due

to noncoincidence of the dipole moment axes and the ILCT transition directions.81

Coe and co-workers have reported a number of studies on the NLO properties of ruthenium

ammine complex salts of pyridyl ligands, focusing on the establishment of SACs for values

derived via 1,064 nm HRS.82–91 Data for (33) and (34) show that 0 of the dye coumarin-510

(33 Â 10À30 esu from EFISHG in CHCl3) is largely unaffected by complexation, attributable to

weak coumarin-metal -electronic coupling arising from the 3-substitution at the pyridyl ring.82

Systematic studies with various salts trans-[RuII(NH3)4(LD)(LA)][PF6]n (LD ¼ an electron-rich

ligand; LA ¼ an electron-deficient ligand; n ¼ 2 or 3)83–89 yield the following conclusions: (i) such

O

n+ [PF6– ]n



O

H3N



N



N



H3N



Ru



n = 2 (33): λ max = 430 nm, β 0[HRS] = 35 × 10–30 esu (MeCN)



NH3



n = 3 (34): λ max = 438 nm, β 0[HRS] = 37 × 10–30 esu (MeCN)82



NH3



H3N



H 3N



NH3

O



Me2N



N



Ru



2+ [PF6– ]2



(35): λ max = 500 nm,



β 0[HRS] = 27 × 10 –30 esu (MeCN)83



N

OEt



H3 N



NH3



H3N



NH3

O



Me2N



C N



Ru



2+ [PF6– ]2



(36): λ max = 472 nm,



N



β 0[HRS] = 53 × 10 –30 esu (MeCN)83



Me

H3N



H3N



NH3



NH3

+



Me2N



N



Ru



N



O



3+ [PF6– ]3



N

Me



N

Me



N



Ru



H3N



β 0[HRS] = 410 × 10 –30 esu (MeCN)85



NH3



H3N



H3N



(37) : λ max = 688 nm,



NH3

N

NH3



+

N



3+ [PF6– ]3



(38) : λ max = 638 nm,

β 0[HRS] = 310 × 10–30 esu (MeCN)86



Nonlinear Optical Properties of Metal Complexes



631



complexes possess large 0 values which are associated with intense, low-energy RuII ! LA

MLCT excitations, (ii) the 0 responses of complexes containing three or more aryl rings

(e.g., (37) and (38)) are very pronounced and considerably larger than those of related species with

only 2 aryl rings (e.g., (35) and (36)), and (iii) the MLCT Emax and 0 values can be finely tuned by

ligand-based changes, in reasonable agreement with the TSM. Perhaps the most interesting result

to emerge from these studies is the observation that the MLCT absorptions and 0 responses of

certain complexes (e.g., (39)) can be reversibly and very effectively (10–20-fold) attenuated

by RuIII/II redox using chemical reagents.87–91 This first clear demonstration of redoxinduced switching of NLO responses provides a novel justification for including transition metal

centers in molecules with large

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