Tuning the Direction of Intramolecular Charge Transfer and the Nature of the Fluorescent State in a T-Shaped Molecular Dyad

Abstract

Controlling photoinduced intramolecular charge transfer at the molecular scale is key to the development of molecular devices for nanooptoelectronics. Here, we describe the design, synthesis, electronic characterization, and photophysical properties of two electron donor-acceptor molecular systems that consist of tolane and BF2-containing curcuminoid chromophoric subunits connected in a T-shaped arrangement. The two π-conjugated segments intersect at the electron acceptor dioxaborine core. From steady-state electronic absorption and fluorescence emission, we find that the photophysics of the dialkylamino-substituted analogue is governed by the occurrence of two closely lying excited states. From DFT calculations, we show that excitation in either of these two states results in a distinct shift of the electron density, whether it occurs along the curcuminoid or tolane moiety. Femtosecond transient absorption spectroscopy confirmed these findings. As a consequence, the nature of the emitting state and the photophysical properties are strongly dependent on solvent polarity. Moreover, these characteristics can also be switched by protonation or complexation at the nitrogen atom of the amino group. These features set new approaches toward the construction of a three-terminal molecular system in which the lateral branch would transduce a change of electronic state and ultimately control charge transport in a molecular-scale device.

Influence of the electron donor groups on the optical and electrochemical properties of borondifluoride complexes of curcuminoid derivatives: a joint theoretical and experimental study

“…Our previous work has shown that the presence of a strong donor group at the meso position induced the occurrence of a low energy charge transfer transition. 36 In contrast, the meso phenyl group in 26 has a triing impact on the HOMO, the terminal methoxyphenyl groups determining the limits of the extension of this orbital. The same observation can be made for compound 29, bearing the ester-functionalized meso phenyl ring (Fig.…”

“…The data for 4, 9, 12, 13, 14, 17, 24, 25, 26, 27, 29 were reported previously by some of us. [32][33][34][35][36] Those for 6, 7, 8 were published by other groups. 27,28 For the sake of comparison, we recorded the spectra of the last three compounds under the same experimental conditions using DCM as solvent and the data we obtained are fully consistent with the published ones.…”

“…52 Previous studies have shown the solvatochromic dependence of absorption and emission properties of borondiuoride complexes of curcuminoids, which is consistent with the partial CT character of the transitions. [32][33][34][35][36] In the case of 1 and 2, containing electronwithdrawing groups, such CT behavior is not observed, their absorption and emission spectra being well-structured and lying at higher energies. As noticed elsewhere, the introduction of a meso aryl unit systematically shis the spectra to the red (ca.…”

Tailoring of spectral response and intramolecular charge transfer in β-enaminones through band gap tuning: synthesis, spectroscopy and quantum chemical studies

“…The study of the ICT process provides us with precious information about the mechanism of many chemical and biological processes involving long-range charge separation, like, photosynthesis and metabolism. [17][18][19] Excited state ICT oen occurs through a p-electron bridge. 6-23 A number of contributions reporting experimental ndings and theoretical calculations on ICT molecules, and more recently, experimental work coupled with quantum chemical calculations have been reported.…”

Recent progress on intramolecular charge-transfer compounds as photoelectric active materials

“…However, only a few researches studied the ICT state based on the other structural properties of molecular frameworks such as substitution position, coplanarity and flexibility [27,28]. In fact, the properties of ICT compounds are influenced by both the intrinsic nature of D/A components and the relative orientation of the components [29]. Through a rational choice of the D-A units and a flexible change of the molecular geometry structures, the electron redistribution, highest occupied molecular orbit (HOMO)-lowest unoccupied molecular orbit (LUMO) energy gap and absorption and emission properties [30,31] of the dipolar molecules could be finely controled.…”