Ensembles of rings with a coumarin unit.

Abstract

We have investigated the luminescent spectral properties of 3- (2-R-thiazol-4-yl)coumarins (R = CH 3, CHeCN, Ar) and some isomeric 3-(4-R-thiazol-2-yl)coumarins (R = Ar) with substituents of different electronic types both in the coumarin and in the aryl moieties. We have obtained estimates of the rate constants for primary photophysical processes: emission of fluorescence and nonradiative degrtdation of the electronic excitation energy. We have calculated the matrix elements for the spin-orbit coupling operator, and based on these matrix elements we have calculated the intersystem crossing rate constants. We have shown that deterioration of the fluorescent properties of the studied thiazolyl derivatives of coumarin when 1r-conjugated moieties are introduced into the thiazole ring is determined by the enhancement of the spin-orbit interaction in a system of levels of the 7r, 7r-type.*For communication 1, see [1].

Nature of Linear Spectral Properties and Fast Relaxations in the Excited States and Two-Photon Absorption Efficiency of 3-Thiazolyl and 3-Phenyltiazolyl Coumarin Derivatives

“…The main spectral parameters and the corresponding values of photodecomposition quantum yields, Φ ph , are shown in Figures – and Table . The steady-state linear one-photon absorption (1PA) spectra of 1 and 2 (Figure , curves 1, 2) revealed relatively weak long wavelength absorption bands at ∼380–395 nm (maximum extinction coefficient, ε max ≈ (24–28) × 10 3 M –1 cm –1 ), with nearly structureless absorption contours and no substantial dependence on solvent polarity, which is typical for 3-thiazolylcoumarins in liquid medium at room temperature. ,, These 1PA bands can be attributed to a single π → π* electronic transition S 0 → S 1 in accordance with nearly constant values of excitation anisotropy r 0 (λ) (see Figure a,b, curves 1) over the spectral range λ ≥ 330–350 nm. These values of r 0 (λ) ≈ 0.3–0.35 are close to the theoretical limit and related to the comparatively small angle between the absorption and emission transition dipoles for S 0 → S 1 and S 1 → S 0 electronic transitions, respectively.…”

“…The development and investigation of different types of coumarin derivatives remain subjects of continuing interest for a number of important research areas, including organic electronics, , nonlinear optics, and lasing, − 3D microfabrication and optical data storage, − sensing technologies, − biomedical probes and reactants, − and one- and two-photon photodynamic therapy (PDT). , Coumarin derivatives exhibit a large variety of linear steady-state and time-resolved photophysical properties, − which depend on the specific substituents in different positions of the molecular architecture ,,,,, and solute–solvent interactions. ,,,,, These characteristics afford the ability to tune emission efficiency, , the values of Stokes shifts, binding abilities, , and photochemical stability along with harnessing the fast relaxation processes in the ground and excited electronic states of coumarins for a number of applications. − It should be mentioned that notable efforts were made for improving and making practical use of the two-photon absorption (2PA) properties of coumarin derivatives in the microfabrication, biomedicine, fluorescence microscopy, and PDT research fields.…”

“… 19 , 20 Coumarin derivatives exhibit a large variety of linear steady-state and time-resolved photophysical properties, 21 − 33 which depend on the specific substituents in different positions of the molecular architecture 18 , 24 , 25 , 27 , 34 , 35 and solute–solvent interactions. 2 , 21 , 22 , 26 , 36 , 37 These characteristics afford the ability to tune emission efficiency, 21 , 38 the values of Stokes shifts, 34 binding abilities, 23 , 39 and photochemical stability 40 along with harnessing the fast relaxation processes in the ground and excited electronic states of coumarins for a number of applications. 28 − 33 It should be mentioned that notable efforts were made for improving and making practical use of the two-photon absorption (2PA) properties of coumarin derivatives in the microfabrication, 41 biomedicine, 42 fluorescence microscopy, 43 and PDT 19 research fields.…”