Environment-Sensitive Behavior of DCNP in Solvents with Different Viscosity, Polarity and Proticity

Dye Stabilization and Wavelength Tunability in Lasing Fibers Based on DNA

Lasers based on biological materials are attracting an increasing interest in view of their use in integrated and transient photonics. Deoxyribonucleic acid (DNA) as optical biopolymer in combination with highly emissive dyes has been reported to have excellent potential in this respect. However, achieving miniaturized lasing systems based on solid-state DNA shaped in different geometries to confine and enhance emission is still a challenge, and the physicochemical mechanisms originating fluorescence enhancement are not fully understood. Herein, a class of wavelength-tunable lasers based on DNA nanofibers is demonstrated, for which optical properties are highly controlled through the system morphology. A synergistic effect is highlighted at the basis of lasing action. Through a quantum chemical investigation, it is shown that the interaction of DNA with the encapsulated dye leads to hindered twisting and suppressed channels for the nonradiative decay. This is combined with effective waveguiding, optical gain, and tailored mode confinement to promote morphologically controlled lasing in DNA-based nanofibers. The results establish design rules for the development of bright and tunable nanolasers and optical networks based on DNA nanostructures.

Highly Polarized Coumarin Derivatives Revisited: Solvent-Controlled Competition Between Proton-Coupled Electron Transfer and Twisted Intramolecular Charge Transfer

Linking a polarized coumarin unit with an aromatic substituent via an amide bridge results in weak electronic coupling that affects the intramolecular electron-transfer (ET) process. As a result of this, interesting solvent-dependent photophysical properties can be observed. In polar solvents, electron transfer in coumarin derivatives of this type induces a mutual twist of the electron-donating and -accepting molecular units (TICT process) that facilitates radiationless decay processes (internal conversion). In the dyad with the strongest intramolecular hydrogen bond, the planar form is stabilized, such that twisting can only occur in highly polar solvents, whereas a fast proton-coupled electron-transfer (PCET process) occurs in nonpolar n-alkanes. The k_PCET rate constant decreases linearly with the energy of the fluorescence maximum in different solvents. This observation can be explained in terms of competition between electron- and proton-transfer from a highly polarized (ca. 15 D) and fluorescent locally excited (¹ LE) state to a much less polarized (ca. 4 D) charge-transfer (¹ CT) state, a unique occurrence. Photophysical measurements performed for a family of related coumarin dyads, together with results of quantum-chemical computations, give insight into the mechanism of the ET process, which is followed by either a TICT or a PCET process. Our results reveal that dielectric solvation of the excited state slows down the PCET process, even in nonpolar solvents.

Tracking mitochondrial viscosity in living systems based on a two-photon and near red probe

A two-photon fluorescence probe, Mito-V, with near-red emission to measure the viscosity changes of mitochondria in living cells and in vivo.

Low-Molecular Push-Pull Pyrazoline Derivatives: Solvatochromic Effect and Theoretical Insights into Dye-based Molecular Engineering

Intermolecular interactions between dyes and solvents are essential in understanding a number of phenomena. In this contribution, we focused on similarities and differences between two molecules belonging to the same pyrazoline derivatives group: the small and rigid- 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1 H-pyrazole (DCNP) molecule and the quite long and flexible one of (4-(2-(1-phenyl-4,5-dihydro-1 H-pyrazol-3-yl)vinyl)benzylidene) malononitrile (PY-PhdiCN). We experimentally show and use theoretical calculations to prove that extension of π-connector significantly changes the electrostatic potential distribution, which results in delocalization of negative charge along the whole donor group and increases potential surface of interaction with solvent molecules giving large spectral shifts. We also show that pyrazoline derivatives are very effective and sensitive solvent indicators with long-time stability.

Enlargement of the organic solid-state DFB laser wavelength tuning range by the use of two complementary luminescent dyes doped into the host matrix

Broad range tunable DFB lasing was achieved by the utilization of two dyes forming molecular aggregates within the polymeric matrix.