Structure-Property Relationships in an Iridium(111) Bis(Terpyridine) Complex with Extended Conjugated Side chains

Iridium(III)-bis-terpyridine complexes are known as excellent triplet emitters with emission lifetimes in the order of microseconds. We report the homoleptic complex [IrL2]3+ (L = 4’-(4-2,5-bis(octyloxy)-4-styrylphenyl)ethinyl)phenyl)-2,2’:6’,2’’-terpyridine) that shows no detectable phosphorescence at room temperature but fluoresces. Emission spectra of [IrL2]3+ depend on the excitation wavelength. The origin of this behavior is studied with the help of results from (TD-)DFT calculations and is attributed to the selective excitation of different rotamers and isomers. Femtosecond-transient absorption experiments give further support for this interpretation as the specific excited-state absorption features of Z- and E-stilbene motives can be identified.