A Deep Understanding on the Effective Generation of Twisted Intramolecular Charge Transfer by Protonation in Thiazolo[5,4-d]thiazole Derivatives

Abstract

The exploration of the intrinsic relationship between the phototautomerization and photoelectric properties is of great significance for the application of the emerging novel organic materials, such as the (bi)heterocyclic thiazolo [5,4d]thiazole derivatives (TzTz). Here, by introducing the chemicalcontrolling protonation, a barrierless spontaneous rotation movement of the designed TzTz derivative (2,5-diyl-amino-thiazolo[5,4d]thiazole, DA-TzTz) was ensured through the facilitation of the excited-state intramolecular proton transfer (ESIPT) triggered twisted intramolecular charge transfer (TICT) process by the enhancement of the intramolecular hydrogen bonds, steric hindrance effect, and conjugative effect. It is further verified that the hetero S atoms could mostly effect the proton accepting ability of −N� through comparing with the influences to the intramolecular H-bond between the protonated/nonprotonated amino groups and the −N� atoms brought by the replacement of them with N or O atoms. As a result, the dissociation and rearrangement of the π conjugation in DA-TzTz accompanying with the variation of the optoelectronic characteristics was benefited from the establishment of the preferential charge-transfer and separation. We expect this tentative study could establish a new concept of designing an efficient charge-transfer and separation method, paving the way for the development of the TzTz derivatives and other optoelectronic organic materials.

Dual emission of ESIPT-capable 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)pyrimidines: interplay of fluorescence and phosphorescence

“…According to previous research on ESIPT-capable compounds, the proton transfer process can lead to a radiationless deactivation via a conical intersection (CI) of non-planar nature (in other words, through a so-called twisted intramolecular charge transfer (TICT) state). 134–144 We noticed that the geometries of the S 1 state with an O–H distance constraint greater than 1.8 Å cannot be optimized due to oscillations around a C Ph –C Pym bond connecting the hydroxyphenyl and pyrimidine moieties. Unconstrained geometry optimization of the S 1 state with l (O–H) > 1.8 Å directly leads to a non-planar geometry (near-CI geometry in Fig.…”

Solvation effect enabled visualized discrimination of multiple metal ions

“…26 Furthermore, due to the energy/ charge transfer between the excited state of the solute molecule and the solvent molecule, the polarity dominantly induced alterations in the uorescence emission wavelength, 27 lifetime, and quantum yield (known as solvatouorochromism) also attract special attention. A recent study shows that ICT character at an excited state for asymmetric thiazolo [5,4-d]thiazole (TTz) [28][29][30] derivatives was strengthened by the solvating effect of a polar solvent, reecting as a decreased quantum yield, an increased lifetime and a bathochromic-shi. As mentioned above, the solvation effect can be studied in depth and promising to be applied to modulate the optical sensing response from either reaction progress or optical properties.…”

Amination and Protonation Facilitated Novel Isoxazole Derivative for Highly Efficient Electron and Hole Separation

“…31−33 Typically, the TICT process is triggered by ESIPT through both the lowering of the torsion barrier by the intramolecular hydrogen bonding and the change in the conjugated system brought by the proton transfer process itself. 34,35 Thus, the synergy of these two processes could not only make the torsional configuration more stable but also ensure an efficient electron−hole separation. Accordingly, the unique properties of the ESIPTtriggered TICT process have been widely used in various functional organic materials.…”

“…The deep understanding of intrinsic logical relations between the configurational variation and photochemical properties of the organic sensitizers has attracted considerable research interest, particularly in areas such as fluorescent dyes, fluorescent sensors, and organic luminescence devices. − As one of the most fundamental and significant configurational variations caused by the excitation-strengthened hydrogen bonds, the excited-state intramolecular proton transfer (ESIPT) shows various photochemical properties involving the intramolecular charge transfer (ICT) process. − The twisted intramolecular charge transfer (TICT) is a unique form of ICT that typically leads to the dissociation of the π-conjugated systems and significant changes in electron density distributions throughout the molecule. − The twisting process, which involves the decoupling of the π-systems between the acceptor and the donor units, could lead to a minimal transition dipole strength between the excited and the ground states, resulting in the formation of a stable TICT state . It has been found that the strategy of utilizing the ESIPT-triggered TICT effectively maintains the torsional advantage between the countering fragments by lowering the molecular energy, which is accompanied by the destruction of the π-conjugation systems and the efficient charge transfer, ensuring a complete charge transfer and separation. − Typically, the TICT process is triggered by ESIPT through both the lowering of the torsion barrier by the intramolecular hydrogen bonding and the change in the conjugated system brought by the proton transfer process itself. , Thus, the synergy of these two processes could not only make the torsional configuration more stable but also ensure an efficient electron–hole separation. Accordingly, the unique properties of the ESIPT-triggered TICT process have been widely used in various functional organic materials. − However, it remains a challenge to extend this strategy to simple and versatile π-conjugated structures consisting of proton donors and acceptors, which is essential to gain insight into the exploration of structural change-related novel sensitizers.…”