Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

Abstract

propanol at room temperature and at 77 K. The fluorescence quantum yield Φ fl of the laser dye DCM increases linearly as the polarity of the binary solvent mixture (toluene+DMSO) increases, from 0.08 in toluene to 0.80 in DMSO. The dependence of Φ fl on the polarity of the mixture toluene+DMSO for DCMF3 and DCMF7 reaches a maximum for a small amount (~2 vol.%) of added polar DMSO; and with further increase in the DMSO concentration (≥50 vol.%), the fluorescence of the fluoro derivatives of DCM is practically completely quenched. The quantum yield for intersystem crossing Φ ST for DCM, DCMF3, and DCMF7 is no greater than 0.01 in solutions of different polarities. We discuss the mechanisms for nonradiative deactivation of the electronic excitation energy for the fluoro derivatives compared with DCM.Key words: laser dye, charge transfer, fluorescence quantum yield, solvent polarity.Introduction. The photophysical properties of organic compounds with electron-donor and electron-acceptor substituents have been widely studied recently [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. They are of interest in connection with their possible application as organic light-emitting diodes in color graphical displays [6], fluorescent labels and visualizing agents in biological systems [7,8], and also owing to their nonlinear optical properties [9, 10] (high quadratic polarizability β). Electron donor/acceptor compounds with effective intramolecular charge transfer are characterized by a large dipole moment in the ground state (µ g ), which generally increases during transition of the molecule to the S 1 state (µ e ), and consequently their photophysical and photochemical properties are determined to a significant extent by the solvent polarity [11].Deactivation of the energy of the excited states of stilbene dyes depends considerably on the polarity and viscosity (stiffness) of the medium. In nonpolar alkane solvents, the absorption and fluorescence spectra of electron donor/acceptor stilbene derivatives have vibronic structure, pronounced mirror symmetry, and a small Stokes shift [12]. The geometry of the molecules in the ground state and the excited state is planar in this case, and emission occurs from a high-lying, locally excited state [13]. Compounds in which rotation of molecular moieties about single and double bonds is possible in nonpolar solvents generally have low fluorescence quantum yield Φ fl [14], and quenching is due to adiabatic transitions to a low-lying non-fluorescent "phantom" state "twisted" about the double bond [13,14]. For model compounds in which internal rotation about the double bond is chemically ruled out [14,15] and for "rigid" coumarin dyes [16-18], a high fluorescence quantum yield has been observed (Φ fl ≥ 0.5) in nonpolar solvents. Φ fl also markedly increases as the viscosity of the nonpolar medium increases, as a result of hindrance of the internal

Using fluorescence dyes as a tool for analyzing the MALDI process

“…Electronic energy trapped in FTraps can be released by fluorescence, internal conversion (IC), photodissociation or intersystem crossing (ISC). Deactivation by means of ISC has only a very low probability, e.g., no greater than 0.01 for DCM [23]. DCM molecules undergo limited photoionization, as indicated by the lack of radical cation signals below amounts of ϳ100 fmol.…”

Protomer-Specific Photochemistry Investigated Using Ion Mobility Mass Spectrometry

“…S 1 ← S 0 orbital excitations for trans-DCM, P1-trans-DCMH + , and P3-trans-DCMH + . The three transitions are HOMO−LUMO in character.The solution absorption spectrum of trans-DCM peaks at 461 nm in toluene (nonpolar solvent) and 466 nm in methanol (polar solvent) 47.…”

Optical Determination of Young’s Modulus of Nanoscale Organic Semiconductor Thin Films for Flexible Devices

“…Because we used XeF 2 gas-phase etching to release the suspended SiO 2 microbeams, we considered the effect of fluorination on the spectral emission properties of an Alq 3 –DCM guest–host system. The photophysical properties of the laser dye DCM are strongly governed by electron transfer between the electron-donating dimethylamino group and electron-accepting pyrene ring. , The addition of fluorine atoms to the electronegative pyrene ring could form fluorinated DCM derivatives that produce bathochromatic shifts in the absorption and fluorescence spectra . We also observed a slight reduction in the fluorescence quantum yield after XeF 2 etching.…”

“…54,55 The addition of fluorine atoms to the electronegative pyrene ring could form fluorinated DCM derivatives that produce bathochromatic shifts in the absorption and fluorescence spectra. 56 We also observed a slight reduction in the fluorescence quantum yield after XeF 2 etching. To avoid any photophysical changes, we evaporated a 50 nm 2,2′,2″-(1,3,5-benzinetriyl)tris(1-phenyl-1H-benzimidazole) (TPBi) thin film as an encapsulation layer, as illustrated in Figure 1b.…”