Controlling photophysics of styrylnaphthalimides through TICT, fluorescence and E,Z-photoisomerization interplay

Abstract

The photophysical properties of naphthalimide dyes NI1-3 with electron releasing 4-methoxy- (NI1), 3,4-dimethoxystyryl- (NI2) and dimethylaminostyryl (NI3) groups are examined in a variety of protic and aprotic solvents. All compounds demonstrate positive solvatochromism in the steady-state absorption and fluorescence spectra. The analysis of the dependence of the Stokes shift on the polarity of the solvent using the Lippert-Mataga equation allowed us to determine the change in the dipole moment upon excitation. The obtained data correspond to the formation of highly polar charge transfer states. Based on the transient absorption spectra and time-resolved fluorescence measurements, the presence of two different emissive states was definitely proved. The primarily formed planar Local Excited (LE) state dominates in non-polar solvents like cyclohexane and toluene where it relaxes mostly through fluorescence and E,Z-isomerisation pathways. In polar solvents, an alternative relaxation channel emerges that consists of twisting around single bond between styryl and naphthalimide fragments, which leads to the formation of a Twisted Intramolecular Charge Transfer (TICT) state. The factors affecting the fluorescence of TICT states are discussed. The observed spectral effects are rationalized using quantum-chemical calculations, X-ray data and NMR spectroscopy.

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

“…Therefore, the temperature dependence of this term was neglected and the Arrhenius equation was written in the The Arrhenius plot of k 1 , the rate coefficient of the CT -TICT process in EG. The squares denote the experimentally determined k 1 values, the red line represents a least square fitting to eqn (19). form, where R is the gas constant and b (in J (cP mol) À1 ) depends on the shape of the turning unit and also on the angle and angular velocity of the rotation.…”

“…Examples for this are NIs with a styrene or phenoxy unit inserted between an electron donor group and their 4-position. 19,20 More frequently, however, the TICT state is dark, leading only to the weakening of the emission from the CT excited state. 21 The TICT of pushpull NIs is of significance in several potential applications, like when these molecules act as polarity 8,9 and viscosity probes, 22 the inhibition of TICT in solid state leads to aggregation induced emission, [23][24][25][26] TICT and E/Z isomerization may occur as simultaneous reactions.…”

“…21 The TICT of pushpull NIs is of significance in several potential applications, like when these molecules act as polarity 8,9 and viscosity probes, 22 the inhibition of TICT in solid state leads to aggregation induced emission, [23][24][25][26] TICT and E/Z isomerization may occur as simultaneous reactions. 19 Despite the fluorescence properties of several NIs have been interpreted in terms of two (a CT and a TICT) interconverting S 1 excited states, a comprehensive photophysical study had lacked on a more simple push-pull derivative to give experimental proof of the formation of TICT state. This motivated us to provide a detailed description of the excited state processes in N-propyl-4-piperidinyl-1,8-naphthalimide (2, see Fig.…”

Visible light-triggered NO generation from Naphthalimide-based probe for photoreceptor-mediated plant root growth regulation

“…The fluorescence quenching is possibly due to the formation of the phenolic group and its interaction with the solvent. 32-33 Further, to verify the effect of light intensity on the NO release rate, we have performed kinetic monitoring of NO release experiment using a neutral density filter and recorded the emission spectra of Ni-NO 2 . As expected, we obtained a plateau after 30 min (Fig.…”

On the Nature of Interplay among Major Flexibility Channels in Molecular Rotors

“…Interest in the photochemistry of twisted ICT molecules, here exemplified by 2-[4-(dimethylamino)benzylidene] malononitrile (BMN) (Figure 1), stems in part from their profitable potential applications in molecular optoelectronics, organic light-emitting diodes (OLEDs), and bright sensor materials, NLO material, 3D optical data storage, and advanced biological and molecular imaging [1]. Photoinduced dynamics of simple CT molecules such as p-(N, N-dimethylamino)benzonitrile (DMABN) [2][3][4][5][6][7][8], some α, β-enenitriles [9,10], ethylene and derivatives [11], and many other types of molecules [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] have been extensively studied. Flexible chromogens exhibit twisted intramolecular charge transfer (TICT), which is an electron transfer process that occurs upon photoexcitation in molecules that usually consist of a donor and acceptor part linked by single bond(s) and/or double bonds.…”