Abstract
Molecules with photoswitchable nonlinear optical (NLO) properties on the nanosecond time scale are attracting considerable attention as potential solid-state components of photonic devices, downsizeable at will, for ultrafast information encoding. In this context, we present here the study of an electron-rich Fe(II) 4-nitrophenylalkynyl complex which possesses a high hyperpolarizability in its singlet ground state and a negative (and presumably much decreased) NLO activity in its first excited MLCT state(s). On the basis of an ensemble of spectroscopic and time-resolved measurements we investigate the ultrafast dynamics for deactivation of the initially populated MLCT singlet state(s) of this particular organometallic complex, which are shown to decay into a metastable triplet state. The purported mechanism is rationalized with DFT calculations. We show that this triplet state, which should also exhibit a strongly diminished hyperpolarizability, is fully formed with a very high quantum yield within 15 ps.