Intersystem Crossing, Photo-Induced Charge Separation and Regioisomer-Specific Excited State Dynamics in Fully Rigid Spiro Rhodammine-Naphthalene/Anthraquinone Electron Donor-Acceptor Dyads

We prepared a series fully rigid spiro electron donor-acceptor orthogonal dyads, with closed form of rhodamine (Rho) as electron donor and naphthalene (Np)/anthraquinone (AQ) as electron acceptor, to access the long-lived triplet charge separation (3CS) state, via the electron spin control method. We found strong dependency of the photophysical property of the dyads on the amino substitution positions of the Np chromophores in the dyads 1,8-DaNp-Rho and 2,3-DaNp-Rho. Nanosecond transient absorption (ns-TA) spectra show the population of the 3LE state (lifetime: 47 μs) for 2,3-DaNp-Rho, however, long-lived 3CS state was observed (τCS=0.62 μs) for AQ-Rho, with a CS quantum yield of ΦCS=58 %. Based on femtosecond transient absorption (fs-TA) spectra, spin orbit charge transfer ISC (SOCT-ISC) is proposed to be responsible for the formation of the triplet states. Time-resolved electron paramagnetic resonance (TREPR) spectra of AQ-Rho indicate the presence of two states, a 3LE state with zero field splitting (ZFS) D parameter of 1400 MHz and E parameter of -410 MHz, formed via radical pair ISC (RP-ISC) and SOCT-ISC mechanism; and a 3CS state with the electron spin-spin interaction in the regime of spin-correlated radical pair (SCRP).

Acetonitrile-induced structure fine-tuning of a trinuclear zinc complex showing multistimuli responsive luminescence

A trinuclear zinc complex (1) exhibits mechanochromic and acidochromic luminescence properties with five-color switching. The structure of complex 2 shows that the acetonitrile molecules induce fine-tuning of the structures compared with 1.

Metal ions-triggered photo-induced fluorescence change in rhodamine B-based photo-responsive complexes

Photo-responsive materials with tunable properties by multiple stimuli have been widely used as molecular machines, molecular logic gates, optical data storages, etc. In this work, we report a rhodamine B-based photo-responsive system, whose properties could be facilely modulated by metal ions (Zn(II), Ni(II) and Hg(II)). These metal ions endow the complexes (L-Zn, L-Ni and L-Hg) with similar photochromic property but distinctly different photo-induced fluorescence change. Upon UV light irradiation, the spirolactam ring in rhodamine B moiety turned from a close form to an open form, along with enlarged conjugated structure with intense absorbance. Interestingly, fluorescence "turn off", "no change" and "turn on" responses were induced by Zn(II), Ni(II) and Hg(II) respectively upon UV light irradiation. Taking advantage of the prominently different characteristics caused by metal ions, different logic gates were designed by simply varying the inputs of metal ions and UV light. This work provided a new strategy for developing multifunctional photo-responsive materials, which were further beneficial for constructing photo-controlled logic gates with tunable performance.

Aggregation-enhanced emissive mechanofluorochromic carbazole-halogen positional isomers: tunable fluorescence via conformational polymorphism and crystallization-induced fluorescence switching

The conformational twist of the carbazole-halogen positional isomers produced blue and green polymorphs with tunable solid-state fluorescence and demonstrated mechanofluorochromism.