Conformational Control of Photoinduced Charge Separation within Phenothiazine−Pyrene Dyads

Abstract

Electron donor-acceptor systems, in which phenothiazine is tethered to pyrene by means of a phenyl bridge, exhibit a dual emission in moderately and very polar solvents. Employing steady-state and time-resolved fluorescence spectroscopy, we were able to provide evidence that the "blue" and "red" emission bands originate from different conformers. The ground-state geometry of the majority species is identical to that found in the crystalline state (the quasi-equatorial conformer). This conformation executes a fast electron-transfer process accompanied by significant structural relaxation. Consequently, its fluorescence exhibits a large solvatochromic shift typical for charge-transfer states. The photophysical properties of the minority species (the quasi-axial conformer) vary significantly with the substitution pattern of the bridging phenyl ring. In part, this difference is related to the orientational factor, κ, governing the rate of energy transfer between the pyrene and phenothiazine moieties. In the para-substituted derivative, fluorescence emission from both the excited phenylpyrene and the phenylphenothiazine subsystem can be observed. In the meta-substituted derivative, fluorescence originates mainly from the primarily absorbing phenylpyrene subsystem. In nonpolar solvent (cyclohexane), the nature of the fluorescing state differs for the para-and meta-substituted compounds. Whereas in the former, the fluorescence originates from the locally excited phenothiazine, it is governed by emission from a structurally modified CT state in the latter derivative. Semiempirical (AM1/CI) molecular orbital calculations with a continuum solvent treatment have been used to investigate the different states involved and provide explanations for the observed results. The calculations reveal the existence of an intermediately populated CT state in which the negative charge is partly localized in the bridge as well as in the pyrene acceptor.

Aggregation-induced delayed fluorescence from phenothiazine-containing donor–acceptor molecules for high-efficiency non-doped organic light-emitting diodes

“…A similar AIE behavior was also observed for PTZ-BP in THF/water mixtures (Figure 3b), whereas the only structural difference between the two compounds is that PTZ-XT contains an oxygen bridge, which Aggregation-induced delayed fluorescence N Aizawa et al restricts the internal rotations in the acceptor unit. Hence, the observed AIE behaviors of PTZ-XT and PTZ-BP are primarily attributed to aggregation-induced restriction of conformational changes in the phenothiazine donor unit [42][43][44] and the rotation around the single bond between the donor and acceptor units.…”

Photo-induced dynamics in a pyrene–isoalloxazine(flavin)–phenothiazine triad

“…1 for structural formula) [41,[64][65][66][67][68] and on the three subchromophores (BMF, PYM, PPT) of PYFPT [40,41,[61][62][63] allow an assignment on the energetic ordering of the frontier molecular orbitals (FMOs), namely highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), as follows: E LUMO (phenothiazine) > E LUMO (pyrene) > E LUMO (flavin) and E HOMO (phenothiazine) > E HOMO (pyrene) > E HOMO (flavin). A qualitative energetic evaluation of the inter-component pathways via photo-induced electron transfer is delineated on the basis of the HOMO/LUMO schemata given in Figs.…”

“…The photo-dynamics of pyrene-phenothiazine with photo-induced charge-separation and conformational relaxation was studied in [64][65][66][67][68]. The photo-dynamics of a pyrene-flavine dyad and of a phenothiazine-flavin dyad were analysed in [63,69] and [62,69], respectively.…”

A DFT and TDDFT investigation of interactions between 1-hydroxypyrene and aromatic amino acids

“…Many aromatic hydrocarbons may form charge transfer complexes in the excited states with amino acids which resemble aromatic amines upon excitation of their p-electronic systems [14][15][16][17][18][19]. Therefore, it is very important to know their interactions with biologically important molecules.…”

“…They are also used as oxygen sensors, DNA intercalators and solar cell components [37][38][39]. As mentioned earlier, functionalized Pyrene derivatives may have mechanical, optical or electrical properties that are different from those of Pyrene [17]. Our former studies on Pyrene and its derivatives have revealed that geometrical structures and molecular orbital energies are affected by the substituents and substitution positions in the Pyrene ring [21,40,41].…”