ORGANOMETALLIC TERTHIOPHENE DERIVATIVES - MODULATION OF THE TERTHIOPHENE CORE OF 5,5''-DIPHENYL-2,2' 5'2''-TERTHIOPHENE VIA [CPRU](+) AND [CP-ASTERISK-RU](+) SUBSTITUENTS/
Dd. Graf et Kr. Mann, ORGANOMETALLIC TERTHIOPHENE DERIVATIVES - MODULATION OF THE TERTHIOPHENE CORE OF 5,5''-DIPHENYL-2,2' 5'2''-TERTHIOPHENE VIA [CPRU](+) AND [CP-ASTERISK-RU](+) SUBSTITUENTS/, Inorganic chemistry, 36(2), 1997, pp. 141-149
We have utilized electrochemical, UV-vis absorption/emission spectrosc
opy, and UV-vis spectroelectrochemistry to investigate the electronic
structure of 5,5 ''-diphenyl-2,2':5'2 ''-terthiophene (Ph(2)Tth) and t
he complexes [Cp/CpRu(eta(6)-Ph(2)Tth)]PF6 and [(Cp/Cp*Ru)(2)(eta(6),
eta(6)-Ph(2)Tth)](PF6)(2) (Cp=cyclopentadienyl; Cp=pentamethylcyclope
ntadienyl). Uncomplexed Ph(2)Tth behaves as if the 2,2':5'2 ''-terthio
phene (Tth) core has two weakly conjugated, sterically blocking phenyl
group substituents. The nature of the phenyl substituents are altered
by complexation with ''Cp/CpRu+'' to create [Cp/Cp*Ru(phenyl)](+) su
bstituents. Electrochemical studies show that Ph(2)Tth exhibits two re
versible oxidation processes that produce the radical cation and dicat
ion forms of the Tth core. The complexes of Ph(2)Tth also exhibit loca
lized Tth core oxidations that have E degrees s shifted to more positi
ve potentials by about 150 mV per metal center. This shift is attribut
ed to the positive charge of a [Cp/CpRu-(phenyl)](+) substituent. The
electronic absorption and emission spectra of the complexes are also
indicative of the Tth chromophore. The lambda(max) of the pi-pi trans
ition for the Tth core is sensitive to the nature of the substituent a
nd is red shifted by metal complexation. The complexes exhibit room te
mperature emission that is quenched by intramolecular processes involv
ing the metal center and additionally by acetonitrile. For the Cp comp
lexes in acetonitrile, quenching leads to decomplexation of Ph(2)Tth;
fur the Cp complexes, no decomplexation is observed. Spectroelectroch
emical studies show that the radical cations of Ph(2)Tth and the monor
uthenated complexes exhibit a small degree of pi-dimerization at room
temperature; the diruthenated complexes show no evidence of pi-dimeriz
ation. Studies of the complexes with [Cp/CpRu(phenyl)](+) substituent
s indicate that the properties of the Tth core can be modulated by the
transition metal substituent(s).