Large Stokes Shifted Far‐Red to NIR‐Emitting D‐π‐A Coumarins: Combined Synthesis, Experimental, and Computational Investigation of Spectroscopic and Non‐Linear Optical Properties

Abstract

Coumarin based push‐pull fluorophores (COM‐1 to COM‐5) bearing thiophene π‐spacer were synthesized having a donor at 7‐position and acceptor at 3‐position. Increasing the π‐conjugation length shifts their fluorescence maxima to the longer wavelength (600–756 nm). All fluorophores exhibit positive emission solvatochromism, fluorescence lifetime is in the range of 1.31 to 2.18 ns, and are high thermal stability. The nonlinear optical behavior was investigated by calculating the first/second‐order hyperpolarizability using a spectroscopic and computational method wherein, COM‐3 shows higher optical nonlinearity (μβCT=987 x 10−48 e.s.u and μβ0=9758 x 10−48 e.s.u.) in DMF. Third‐order nonlinear optical parameters measured using the Z‐scan method in each closed and open aperture curves. The fluorophores possess the self‐focusing effect and show negative nonlinear absorption coefficient (β) and positive nonlinear refractive index (n). Among all fluorophores, COM‐5 shows better real part of third‐order susceptibility χ(3) in DMSO (8.58 x 10−13 e.s.u.). Bond length alternation (BLA), natural bond orbital analysis (NBO), and generalized Mulliken‐Hush (GMH) analysis were studied to give theoretical evidence to the effective charge transfer (CT). Quadratic optical nonlinearity and Z‐scan results show that these coumarin‐based fluorophores can be considered as promising candidates for organic NLOphores in material for nonlinear optics.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

“…Instead of merely extending π-conjugation, the approach for coumarin derivatives includes expanding the π-conjugation, which involves side-chain modifications or the secondary introduction of auxiliary side chains, coupled with increased electronic delocalization to achieve a red-shifted emission wavelength [ 210 ]. However, this NIR emission often necessitates stronger interferometric contrast transfer (ICT) and a robust electron acceptor group [ 211 ]. 3).…”

Strategies to convert organic fluorophores into red/near-infrared emitting analogues and their utilization in bioimaging probes

“…Instead of the ring fusion to extend the electron delocalization as shown with benzocoumarins, we can also extend pi-conjugation simply by inserting vinyl groups between the C-3 substituent and the coumarin ring, although such an approach does not guarantee that the vinyl-containing acceptors have sufficient stability to certain reactive biological species (reactive oxygen and nitrogen species) and also to photochemical reactions. 85 Not only the vinyl group 86 but also other groups are possible for the pi-extension, such as alkynyl, 87 thiazole, 88 thiophene, 89 benzothiadiazole, 90 or a combination of them. 91 For example, when a coumarin was subjected to the vinyl extension strategy with a pyridinium acceptor, its emission maximum was red-shifted from 450 nm to 650 nm.…”

Coumarin and Hydroxyl Decorated Viscosity Sensitive Triphenylamine Derivatives: Synthesis, Photophysical Properties, Viscosity Sensitivity, TD‐DFT, and NLO Properties

“…and they have applications in optoelectronics and also inbiological research, data storage, telecommunication . Nowadays there is a great deal of interest in the designing chromophores with strong nonlinear optical properties in the red region . Due to its high photostability, very high quantum yield and high solubility in organic solvents, a large number of coumarin derivatives are studied as fluorescent probes, fluorescent sensors, in cell imaging, as well as in the field of nanotechnology, and optoelectronics, Simultaneously they have wide uses in the arena of “Organic Light Emitting Diodes” (OLEDs), “Dye Sensitized Solar Cells” (DSSCs), dye lasers, optical brighteners, non‐linear optical (NLO) materials, and in biological labeling, Photophysical properties of coumarins can be tuned to red emission by the attachment of electron donating group at 7 positions, electron accepting group at 3 and 4 positions, as well as rigidification ofthe donor or acceptor, and increasing the length of conjugation .…”

“…Organic push pull NLOphores with low refractive index, dielectric constant, rapid response time with electrooptic effect, noncentrosymmetric, asymmetric polarization are synthesized recently, NLOphores having different functionalities show response to different stimuli like mechanochromism FMR and AIEE. and they have applications in optoelectronics and also in biological research, data storage, telecommunication, Nowadays there is a great deal of interest in the designing chromophores with strong nonlinear optical properties in the red region . Due to its high photostability, very high quantum yield and high solubility in organic solvents, a large number of coumarin derivatives are studied as fluorescent probes, fluorescent sensors, in cell imaging, as well as in the field of nanotechnology, and optoelectronics .…”

“…Photophysical properties of coumarins can be tuned to red emission by the attachment of electron donating group at 7 positions, electron accepting group at 3 and 4 positions, as well as rigidification of the donor or acceptor and increasing the length of conjugation . Recently, CN‐substitution effect on coumarin core and their NLO properties have been carried out by experimental and theoretical calculations Coumarin based NLO push‐pull system possessing donor at 7 positions and acceptor at 3 positions with thiophene unit as π‐spacer were prepared and their NLO characteristics were examined by z scan experiment as well as computational method . Triphenylamine is a widely used strong electron donor and widely employed in the design of organic sensitizers in the DSSCs, OLEDs, as fluorescent sensors and in bioimaging .…”