Solvent effects on the photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one

Abstract

The photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one was studied in different solvents and in SDS micelles. This compound presents characteristics which include an S(0)---> S(1) ( pi,pi*) transition with a (1)(n,pi*) perturbative component, due to the electronic coupling between the diethylamino group and the coumarin ring, considerable solvatochromism, dual fluorescence and high fluorescence quantum yields in almost all solvents studied. The electronic structure of the S(1) and S(2) excited states permits vibronic coupling between them, making configurational changes of the S(2) excited state possible, leading to the formation of an S(2)(TICT) state. Analysis of the TCSPC data indicates an equilibrium between the S(2)(TICT) and S(1)(LE) states in favour of the former. In protic solvents, the hydrogen bonding between the solvent and the diethylamino moiety results in the formation of an S(2)(HICT) state, making internal conversion an important deactivation process. Quantum mechanical calculations for the isolated molecule show that the diethylamino group in the S(2)(TICT) state is twisted at least 56 degree from the plane of the coumarin ring, with partial electronic decoupling between -NEt(2) and the coumarin ring. This twisting angle must be positively influenced by solute-solvent interactions. [capital Phi](ST) is found to be small, but not negligible. However, Phi (delta) can be considered negligible, an indication that T(1) is a short-lived state. Based on the experimental data and theoretical calculations, the most probable sequence for the first excited states, including the TICT state, is T(1)(n, pi*) < S(2)(TICT) < S(1)(pi,pi*) approximate S(2) (n,pi*).

Theoretical and NMR structural characterisation of a polymorphic azo dye

“…The electronic coupling between N(24) and the aromatic ring implies in the participation of the non-bonding p-orbital of nitrogen in the π system of the aromatic ring, and gives to the nitrogen a partial sp 2 character. This characterizes an intramolecular charge-transfer state [13]. Table 2).…”

“…In order to confirm the NMR data of both A and B conformers of compound (1) in solution, a solid state 13 C NMR spectrum of this sample was acquired. The analysis of the CP-MAS NMR spectrum confirms the presence of two conformers and the carbon resonances obtained in this spectrum fits quite well with those of the solution spectrum ( Table 3).…”

“…Chemical shifts (δ) are reported in ppm, coupling constants (J) are in hertz and the internal standard was TMS. 13 C Assignments were made with the aid of 2D gHSQC and gHMBC (delays for one bond and long-range J C/H couplings were optimised for 145 and 7 Hz, respectively) experiments.…”

“…HSQC spectra give 1 J C/H correlations while HMBC spectra allowed the establishment of connectivities between coupled proton and carbons two to three bonds a way from each other. 13 C CP-MAS NMR spectra were recorded at 100.62 MHz on a Bruker Avance 400 spectrometer with the following conditions: 5 s of recycle delay, 1.5 ms of time contact, 90º pulse of 5 µs and AQ of 33.8 ms. In the dipolar dephasing experiment a contact time of 50 µs was used.…”

An enolato-bridged dinuclear Cu(ii) complex with a coumarin-assisted precursor: a spectral, magnetic and biological study

“…They show that H 2 L fluoresces strongly when it's pp* transition band is excited, whereas complex 1 is a weak emitter (Fig. The Stokes shift parameter indicates the difference in properties and structure between the ground state S 0 and the first exited state S1, 56 and has been estimated according to the following equation: 57 Du 0 = u abs 0 À u em 0 = (1/l abs À 1/l em ) Â 10 7 cm À1 For H 2 L, a strong emission band appears at 498 nm upon excitation at 314, 347 or 383 nm (which are pp* bands).…”