Accurate Analysis of Spectrophotometric Data to Quantify the Photoswitching Performance of a Biomimetic / Light-Induced Molecular Switch.

Photoswitches are widely investigated molecules because upon exposure to selected light irradiation, they are able to undergo structural, and hence optical, changes. To fully exploit their responsiveness to irradiation, the quantum efficiency of the forward and back reactions is a fundamental parameter, whose accurate determination is critical. In this work, the spectral evolution of a biomimetic switch, which undergoes / photoinduced isomerization, is spectrophotometrically examined.

Unlocking the Potential of Push-Pull Pyridinic Photobases: Aggregation-Induced Excited-State Proton Transfer.

The pH effect on the photophysics of three push-pull compounds bearing dimethoxytriphenylamine (TPA-OMe) as electron donor and pyridine as electron acceptor, with different ortho-functionalization (-H, -Br, and -TPA-OMe), is assessed through steady-state and time-resolved spectroscopic techniques in DMSO/water mixed solutions and in water dispersions over a wide pH range. The enhanced intramolecular charge transfer upon protonation of the pyridinic ring leads to the acidochromic (from colorless to yellow) and acido(fluoro)chromic (from cyan to pink) behaviours of the investigated compounds. In dilute DMSO/buffer mixtures these molecules exhibited low pK values (≤3.

Intramolecular Singlet Fission Coupled with Intermolecular Triplet Separation as a Strategy to Achieve High Triplet Yields in Fluorene-Based Small Molecules.

In this work, detailed experimental proof and in-depth analysis of the singlet fission (SF) mechanism, operative in fluorene-based small molecules, are carried out by employing advanced time-resolved spectroscopies with nanosecond and femtosecond resolution. The investigation of the effect of solution concentration and solvent viscosity together with temperature and excitation wavelength demonstrates INTRAmolecular formation of the correlated triplet pair followed by INTERmolecular independent triplet separation via a "super-diffusional" triplet-triplet transfer process. This unconventional INTRA- to INTERmolecular SF may be considered an "ideal" mechanism.

Unveiling the double triplet nature of the 2Ag state in conjugated stilbenoid compounds to achieve efficient singlet fission.

In this investigation, the excited-state evolution in a series of all-trans stilbenoid compounds, displaying a low-lying dark singlet state of 2Ag-like symmetry nearly degenerate with the bright 1Bu state, was unveiled by employing advanced ultrafast spectroscopies while probing the effect of solvent polarizability. Together with the dual emission, femtosecond transient absorption and broadband fluorescence up-conversion disclosed the double nature of the 2Ag-like state showing both singlet features, a lifetime typical of a singlet and the ability to emit, and a triplet character, exhibiting a triplet-like absorption spectrum. The ultrafast formation (in hundreds of femtoseconds) from the non-relaxed upper singlet state led to the identification of 2Ag as the correlated triplet pair of singlet fission.