Photoinduced Charge Transfer and Bimetallic Bond Dissociation of a Bi-W Complex in Solution

Elucidating Inner Workings of Naturally Sourced Organic Optoelectronic Materials with Ultrafast Spectroscopy

Recent advances in sustainable optoelectronics including photovoltaics, light-emitting diodes, transistors, and semiconductors have been enabled by π-conjugated organic molecules. A fundamental understanding of light-matter interactions involving these materials can be realized by time-resolved electronic and vibrational spectroscopies. In this Minireview, the photoinduced mechanisms including charge/energy transfer, electronic (de)localization, and excited-state proton transfer are correlated with functional properties encompassing optical absorption, fluorescence quantum yield, conductivity, and photostability. Four naturally derived molecules (xylindein, dimethylxylindein, alizarin, indigo) with ultrafast spectral insights showcase efficient energy dissipation involving H-bonding networks and proton motions, which yield high photostability. Rational design principles derived from such investigations could increase the efficiency for light harvesting, triplet formation, and photosensitivity for improved and versatile optoelectronic performance.

Excited-State Dynamics of a meta-Dimethylamino Locked GFP Chromophore as a Fluorescence Turn-on Water Sensor†

Strategic incorporation of a meta-dimethylamino (-NMe₂ ) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m-NMe₂ -LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ˜200-fold decrease in fluorescence quantum yield of m-NMe₂ -LpHBDI in alcohols (e.g., MeOH, EtOH and 2-PrOH) supports this GFP-derived compound as a fluorescence turn-on water sensor, with large fluorescence intensity differences between H₂ O and ROH emissions in various H₂ O/ROH binary mixtures. A combination of steady-state electronic spectroscopy, femtosecond transient absorption, ground-state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen-bonding chain between a solvent -OH group and the chromophore phenolic ring -NMe₂ and -OH functional groups, wherein fluorescence differences arise from an extended hydrogen-bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge-transfer state. The absence of a meta-NMe₂ group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without the meta-NMe₂ group or with both meta-NMe₂ and para-OH groups locked in a six-membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors.

Segmented Ag-Au-Ag Heterojunction Nanorods: Pressure-Assisted Aqueous-Phase Synthesis and Engineered Femtosecond-to-Nanosecond Dynamics

Segmented metal-metal heterostructure nanorods/nanowires are very promising for development in photoelectric devices, wearable electronics, biomedicine, and energy storage due to unique surface and interface and adjustable electronic and optical properties. Regretfully, most of the segmented heterojunctions are presently synthesized in organic solvent, and its electronic dynamics is still rarely studied and poorly understood. Here, we reported a pressure-assisted one-step aqueous-phase strategy to successfully synthesize segmented Ag-Au-Ag heterojunction nanorods (HJNRs), the aspect ratios and heterojunction contents of which can be well controlled by varying pressure value. The heterojunction-induced femtosecond-to-nanosecond dynamics in 1D direction of the Ag-Au-Ag HJNRs were for the first time acquired and presented a unique regularity tendency (e.g., electron-phonon scattering time). The unprecedented aqueous-phase strategy opens up horizons of synthesis of other segmented metal-metal HJNRs, and the fascinating Ag-Au-Ag HJNRs are hopeful for the development of a new class devices in photothermal and photoelectronic fields.