Organometallic complexes for nonlinear optics. 39. Syntheses and third-order nonlinear optical properties of first-generation peripherally metalated arylalkynyl dendrimers

Steric control of the extent of reaction has been developed to rapidly synthesize ligated metal-containing dendrons that have been employed in arylalkynyl complex dendrimer synthesis. Reaction of 1,3,5-triethynylbenzene with excess cis-[RuCl(2)(dppe)(2)] affords 1,3-{trans-[(dppe)(2)ClRuCC]}(2)-5-HCCC(6)H(3) (1). Reaction of 1 with 4-RC(6)H(4)CCH affords 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-HCCC(6)H(3) [R = H (2a), NO(2) (2b), NH(2) (2c)]. 2a-care coupled with 4-Me(3)SiCCC(6)H(4)I under Sonogashira conditions to give 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-(Me(3)SiCCC(6)H(4)-4-CC)C(6)H(3) [R = H (3a), NO(2) (3b), NH(2) (3c)], which can be desilylated to afford 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-(HCCC(6)H(4)-4-CC)C(6)H(3) [R = H (4a), NO(2) (4b), NH(2) (4c)]. Sonogashira coupling of 4a-c with 1,3,5-triiodobenzene gives the systematically varied peripherally metalated arylalkynyl dendrimers 1,3,5-(3,5-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)C(6)H(3)-1-CCC(6)H(4)-4-CC)(3)C(6)H(3) [R = H (5a), NO(2) (5b), NH(2) (5c)]. All complexes show two reversible oxidation processes by cyclic voltammetry. Cubic nonlinearities determined using the Z-scan technique and low-repetition femtosecond pulses at 660 and 800 nm increase on pi-system lengthening and progression from dendron to dendrimer. In contrast to all other complexes in this study, 5b is a saturable absorber at 800 nm. Dispersion of both the refractive and the absorptive nonlinearities of 5b has been determined, and the behavior has been modeled for the first time with an inorganic complex.