Synthesis of a 5-Carboxy Indole-Based Spiropyran Fluorophore: Thermal, Electrochemical, Photophysical and Bovine Serum Albumin Interaction Investigations

Optimizing cyanine dye properties for enhanced dyeing and inkjet printing on diverse Substrates: Photophysical and colorimetric investigations

Cyanine-based cationic dyes with different substituents in the donor unit were easily synthesized using readily available starting materials. The prepared dye molecules were spectroscopically characterized by NMR, FT-IR, and HR-Mass, and their thermal stability was measured by TGA, DSC, and XRD. Based on the TGA and DSC measurements, it was concluded that all the dyes are thermally stable up to 200 °C. Also, powder XRD was studied for all dyes to identify the explicit crystallinity and morphological nature of the dyes. A dye dispersion solution was prepared for the proper dyeing of modacrylic fabric and the dyed fabric showed good color strength K/S for dyes R1, R2, and R6 and fragile color strength for R3, R4,and R5. These dyes are also used for printing on substrates like paper and fabric using ink-jet printing. These dyes were also used for transferability printing applications on various fabrics.

Is this how bromine spiropyran salt is converted to merocyanine under UV irradiation? A look through the prism of quantum chemical calculations

The stability of merocyanine forms formed under UV irradiation of a solution of a spiropyran salt, in which an organic part acts as a cation and a compact bromide ion as an anion, their photophysical properties, and the formation mechanism are studied in this work using time-dependent density functional theory. Theoretical calculations show that TTC and CTT are the most stable open forms (the difference in stability energies is 10.5 and 12.0 kcal mol-1 relative to the formation energy of spiropyran, respectively). The simulated absorption bands in the UV spectrum of the merocyanine forms are observed both in the UV region at 308-366 nm and in the visible region at 544-757 nm due to n → π* and π → π* type transitions. We found that the isomerisation mechanism of spiropyran into merocyanine forms includes two key stages: the ring opening to form cisoid merocyanine forms (except unstable TCC) through conical intersection and their subsequent isomerisation to form stable transoid isomers. The length of the Cspiro-O bond is 1.97 Å and the C1'-C2'-C3'-C4' angle is 70° in the structure close to conical intersection. The stage that determines the rate of this process is the isomerisation between transoid forms, as in the case of transformation of open merocyanine forms into spiropyran.

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

This joint experimental-theoretical work focuses on molecular and photophysical properties of the spiropyran-containing amphiphilic molecule in organic and aqueous solutions. Being dissolved in tested organic solvents, the system demonstrates positive photochromism, i.e., upon UV stimulus the colorless spiropyran form is transformed into colorful merocyanine isomer. However, the aqueous solution of the amphiphile possesses a negative photochromism: the orange-red merocyanine form becomes thermodynamically more stable in water, and both UV and vis stimuli lead to the partial or complete photobleaching of the solution. The explanation of this phenomenon is given on the basis of density functional theory calculations and classical modeling including thermodynamic integration. The simulations reveal that stabilization of merocyanine in water proceeds with the energy of ca. 70 kJ mol−1, and that the Helmholtz free energy of hydration of merocyanine form is 100 kJ mol−1 lower as compared to the behavior of SP isomer in water. The explanation of such a difference lies in the molecular properties of the merocyanine: after ring-opening reaction this molecule transforms into a zwitterionic form, as evidenced by the electrostatic potential plotted around the opened form. The presence of three charged groups on the periphery of a flat conjugated backbone stimulates the self-assembly of merocyanine molecules in water, ending up with the formation of elongated associates with stack-like building blocks, as shown in molecular dynamics simulations of the aqueous solution with the concentration above critical micelle concentration. Our quantitative evaluation of the hydrophilicity switching in spiropyran/merocyanine containing surfactants may prompt the search for new systems, including colloidal and polymeric ones, aiming at remote tuning of their morphology, which could give new promising shapes and patterns for the needs of modern nanotechnology.