An Insight of Molecular Twisting of Coumarin Dyes

Abstract

This article highlights the recent understanding of twisted intramolecular charge transfer state (TICT) of coumarin dyes on TiO 2 and Au NP surface. The natural origin of coumarin dye in several plants makes it attractive to solar cell and fluorescence sensing applications. Two different classes of D-π-A coumarin dyes, having cyano-acrylic acid as acceptor and 7-amino moiety as a donor, have been chosen: one of them, having 7-amino moiety in the ring, shows only intramolecular charge transfer (ICT) states in the excited state. While due to twisting of the free 7-amino moiety, the second class of coumarin shows both ICT and TICT states in their photo-excited states in the polar environment, in the form of a strong dual-fluorescence. On TiO 2 surface such coumarin dyes found to couple with carboxylic moiety, however on Au NP surface they bind with amino moiety. As a result, on TiO 2 surface, the 7-amino moiety is free to rotate, thus exhibiting TICT state which is a charge-separated state and leads to higher electron injection yield for the second class of coumarins. The applicability of such twisted conformers of coumarin molecules in the solar cell has been demonstrated. Furthermore, due to molecular coupling with the 7-amino moiety on Au NP surface, a restriction imposed on the molecular twisting of the free 7-amino group. This constrains the formation of the TICT state for the second class of coumarins on the Au NP surface. Such ICT-TICT fluorescence modulation character of the coumarin dyes may lead them to use for fluorescence sensing application, which is also demonstrated to detect specific ions and biomolecules. Thus the present review acmes very fundamental photophysical properties of coumarin dyes based on their molecular twisting on different solvents, semiconductors, and metal nanoparticles which have great consequences of real life applications.

Aza-BODIPY-based polymeric nanoparticles for photothermal cancer therapy in a chicken egg tumor model

“…In the excited state, AZB-CF 3 demonstrated obvious electron cloud migration from the dimethylaminophenyl moiety in the HOMO to the aza-BODIPY backbone in the LUMO, while their planes were arranged perpendicular to each other, indicating the TICT state. 47 The low energy gap of 1.20 eV obtained from this calculated method agrees well with that acquired from the experimental method (0.93 eV).…”

Inactivation of Competitive Decay Channels Leads to Enhanced Coumarin Photochemistry

“…In coumarin fluorophores substituted like the one shown in Figure 2b, it is known that the molecule can adopt an intramolecular charge transfer (ICT) state. [30][31][32] After excitation, a rotation around the CÀ N bond at the donor moiety can occur. Thereby, repulsive interactions are minimized and charge separation is stabilized.…”

Mitochondria-Targeting Multifunctional Fluorescent Probe toward Polarity, Viscosity, and ONOO– and Cell Imaging

“…In the low-viscosity system, the single bond between the coumarin part and the pyridine part of DPB rotates freely. This rotation causes the two parts to be not in the same plane and accompanied by charge separation. , At this time, the probe mainly occurs to nonradiative transition leading to energy loss, and its fluorescence intensity is weak . Under high viscosity conditions, inhibiting TICT formations via limited rotation of the single bond recovers the charge transfer, resulting in enhanced fluorescence. , The signals of viscosity and ONOO – changed at the same emission wavelength of 658 nm, but the difference was that the fluorescence intensity increased with the increase of viscosity and decreased with the increase of ONOO – , and the completely opposite signal changes avoided false positive signals of viscosity and ONOO – .…”