Experimental evidence of TICT state in 4-piperidinyl-1,8-naphthalimide – a kinetic and mechanistic study

Abstract

The excited state processes in N-propyl-4-piperidinyl-1,8-naphthalimide have been studied by measuring its fluorescence spectra and decay curves in solvents of different polarity and viscosity and also in a frozen solvent glass. The results unanimously proved the formation of a dark twisted intramolecular charge transfer (TICT) state from the emissive charge transfer (CT) species, the direct product of excitation. The rate coefficients of the TICT process and the deactivations of the CT and TICT species were determined, using a reversible two-state kinetic model. The temperature dependence of the kinetic data was consistent with a kinetic barrier consisting of three terms, the inherent barrier of the reaction, and the contributions of the solute-solvent interactions related to the solvent viscosity and polarity. The potential energy surfaces were calculated in the S0 and the S1 states along the coordinate of turning motion which was conclusive concerning the direction of the twisting and indicated a possible conformational change of the piperidinyl unit. The theoretical calculations confirmed that the TICT species is dark and has a stronger charge transfer character compared to the CT state.

Strong ion pair charge transfer interaction of 1,8-naphthalimide–bipyridinium conjugates with basic anions – towards the development of a new type of turn-on fluorescent anion sensors

“…The photophysics of NI and PiNI was investigated in detail in a previous study. 26 Here we only underline that the longest wavelength absorption band as well as the fluorescence band of NI show a substantial redshift in the spectra of PiNI: the absorption band from 331 nm to 405 nm and the fluorescence band from 375 to 535 nm. The absorption spectra of the dyads, NIV and PiNIV are almost the linear combinations of the spectra of MV and the respective naphthalimide reference compounds, NI and PiNI, which indicates only a weak coupling between the electronic structures of the donor and acceptor moieties of the conjugates.…”

“…33 The decay of PiNI is consistent with the conversion of the directly excited emissive molecule into a dark TICT species. 26 The decays of the naphthalimide-viologen dyads, NIV and PiNIV, are triexponential, with two time constants close to the values of the time constants of the respective naphthalimides and an additional fast component (8 ps for NIV, at the limit of the temporal resolution of the TCSPC system, 55 ps for PiNIV) which are associated with the reversible formation of the biradical species from the singlet species. As these time constants are one and two orders of magnitude shorter than the other two time constants of the respective dyads, their reciprocals can be taken as the estimated values of the rate coefficients of the intramolecular electron transfer processes.…”

“…The reference compounds NI and PiNI show biexponential decays in MeCN. 26 Presumably, the deactivation of NI involves an efficient S 1 -T 2 intersystem crossing. 33 The decay of PiNI is consistent with the conversion of the directly excited emissive molecule into a dark TICT species.…”

Solvent Polarity Dependent Excited State Dynamics of 2′-Hydroxychalcone Derivatives

“…Previous comprehensive theoretical studies proposed that excited state relaxation involving intramolecular twist in the excited enol and keto state is responsible for ultrafast deactivation of DEAHC , the torsional angle around hydroxyphenhyl ring located an excited minimum at ∼40°, ,, where the initial conformations in the ground state and FC state are near planar as mentioned above. The intramolecular structural torsion of excited DEAHC can be evidenced by the temperature-dependent fluorescence spectra in ethylene glycol, where the ethylene glycol at higher temperature is reported to have lower viscosities. , As can be seen in Figure S10, the fluorescence intensity becomes weaker at higher temperature, but the shape of spectra did not change, suggesting a deactivation channel via a dark structural twisting species, where the twist of hydroxyphenhyl ring is favored at low viscosities. , Anyway, in DEAHC with the presence of IMHBs, the molecular conformational inflexibility may also lead to efficient ESIPT reaction. To see how structural twist and ESIPT of DEAHC occur during the excited state relaxation, three solvents with different polarities (CHX, THF, and ACN) are also employed for resolving excited state dynamic of DEAHC by using femtosecond transient absorption spectroscopy.…”

Lighting Up the Invisible Twisted Intramolecular Charge Transfer State by High Pressure

“…TICT state is an emission state in some molecules like p - N , N -dimethylaminobenzonitrile (DMABN), which was proposed by Grabowski to explain the anomalous emission . Especially, the TICT state also exhibits nonfluorescent and low-fluorescence phenomena. − For the nonfluorescent TICT molecules, effectively lighting up the invisible TICT state is crucial for developing a variety of promising applications, such as fluorescing probes, optical sensors, and solar energy harvesting devices. − Previous works on visualizing the TICT state have involved molecular structure modifications, such as altering the substituted position or rigidifying the torsional group. , However, on the basis of the intrinsic molecular configuration, the ability to tune the TICT state from invisible to visible has yet to be realized. Understanding the mechanism for how to achieve in situ regulation of TICT fluorescence can further provide a critical step toward promising optoelectronic and biomedical applications.…”