Computer‐Aided Design of Fluorinated Flavin Derivatives by Modulation of Intersystem Crossing and Fluorescence

Abstract

This study aims at finding fluorinated flavin derivatives with modified intersystem crossing (ISC) and fluorescence properties. In total, photophysical properties of 8 derivatives were investigated computationally using combined density functional theory and multireference configuration interaction methods. On top of a screening procedure, the excited‐state decay mechanisms of selected chromophores were investigated in detail. Kinetic schemes including fluorescence, ISC as well as internal conversion (IC) channels were set up to unravel the complex excited‐state decay kinetics. We find two chromophores that exhibit promising properties with respect to fluorescence microscopy. Distinctive stabilization of the bright S1 ππ* state results in absorption in the green wavelength region and emission of (infra‐)red light. The 1(πHπL)⤳3(πH–1πL) ISC channel of the flavin chromophore was found to be deactivated upon both modifications, but nonradiative deactivation of the fluorescence by IC appears to be a problem. Alternative modifications of the pteridine dione moiety were found to result in a marked stabilization of nπ* states along with activation of El‐Sayed allowed ISC channels. For the latter two compounds, we predict fluorescence to be quenched by ISC followed by efficient population of the long‐lived T1 state via IC.

A Thermally Activated Delayed Fluorescence Emitter Investigated by Time‐Resolved Near‐Infrared Spectroscopy

“…rISC and ISC transitions in TADF emitters can be mediated by vibronic mixing with higher excited singlet (S n>1 ) and triplet (T n>1 ) states into lower‐energy excited states (S 1 and T 1 ). According to perturbation theory, the energy gaps between the lower‐energy excited states and higher ones ought to affect this mixing [8] . Here, it has been shown that, for a prototypical TADF emitter, the respective gaps are accessible experimentally by time‐resolved NIR spectroscopy.…”

“…According to perturbation theory, the energy gaps between the lower-energy excited states and higher ones ought to affect this mixing. [8] Here, it has been shown that, for a prototypical TADF emitter, the respective gaps are accessible experimentally by time-resolved NIR spectroscopy. The respective transition energies and oscillator strengths were well reproduced by quantum chemical computations.…”

“…These expressions reveal an explicit and implicit (see, e. g., discussion in ref. [8] ) influence of the energetic separation of CT and locally excited (LE) states (Figure 1 ) on these rate constants. Thus, it seems worthwhile to address the respective energies experimentally.…”

Enhanced Solid-State Fluorescence of Flavin Derivatives by Incorporation in the Metal-Organic Frameworks MIL-53(Al) and MOF-5

“…The absorption spectra typically show four bands with high molar absorptivities (>10 4 L −1 mol cm −1 ) which are attributed to π → π * excitations [ 12 , 13 , 14 ]. The exact position of the absorption maxima, the absorptivity and the photoluminescence quantum yield depend significantly on the chemical structure of the flavin derivative and the chemical-physical environment, including solvatochromic effects [ 11 , 12 , 15 , 16 ].…”

Enhanced Solid-State Fluorescence of Flavin Derivatives by In-Corporation in the Metal-Organic Frameworks MIL-53(Al) and MOF-5

“…The absorption spectra typically show four bands with high molar absorptivities (> 10 4 L -1 mol cm -1 ) which arise from π→π* transitions [12,13,14]. The exact position of the absorption maxima, the absorptivity and the photoluminescence quantum yield depend significantly on the chemical structure of the flavin derivative and the chemical-physical environment, including solvatochromic effects [11,12,15,16]. In their neat solid state, the photoluminescence of dye molecules is often quenched by nonradiative processes.…”