Multiple Emissions of α-Naphthil: Fluorescence from S₂ State

Abstract

Multiple emissions of α-naphthil are reported in solution phase at room temperature as well as in ethanol glassy matrix at 77 K, frozen under different conditions of illumination. Steady state and time-resolved fluorometric measurements are undertaken to assign the observed emissions to the different species in terms of geometry and electronic states of the fluorophore. The unexplored emission band peaking at ∼423 nm has been ascribed to originate from the S2 electronic state. Exhaustive experiments reveal that while the trans conformer of α-naphthil gives only the S1 emission, the conformation with a geometry close to the ground state one emits from both S1 and S2 electronic states depending on the excitation wavelength.

A study on the photophysics of 9-amino-10-cyanoanthracene: probing its dual absorption and emission behavior

“…35,39 Fluorescence from higher excited states is also reported for some other chromophores like aromatic acenes, polyenes, thioketones and metalloporphyrins. [40][41][42] In the case of ACAN, it has been proposed that the S 2 emission arises because of the poor electronic coupling between the S 2 and S 1 states (due to large conformational differences as discussed below), which reduces the radiationless deactivation of S 2 to the S 1 state. 31 Our present observation that the fluorescence decays of the two emission bands, EI and EII, are not correlated, also suggests that the S 2 and S 1 states of ACAN are not coupled with each other.…”

Photophysics of Anthril in Fluids and Glassy Matrixes

“…Room temperature emission studies of 1,2-dicarbonyl compounds benzil and αnaphthil gives emission from the S 2 state, apart from the emissions for two differently emitting rotameric species in the S 1 state. 11,12 On the contrary, α-furil and 2,2′-pyridil give only two fluorescence bands for two different emissive species in the S 1 state. Arguably, with the observation of multiple fluorescence for the 1,2-dicarbonyl compounds, the higher energy fluorescence of anthril having a maximum at 357 nm in EtOH and at 347 nm in MCH may originate either from the higher excited electronic state (S 2 ) or from a different conformer in the S 1 state.…”

“…For the assignment of the fluorescence and phosphorescence emission bands of the fluorophore, we have selected different time windows (depending on the fluorescence and phosphorescence lifetimes) at 77 K frozen matrixes to segregate both these bands precisely. [11][12][13][14]17 Importantly, coexistence of the two isomeric fluorescences and phosphorescences from the same electronic states (S 1 and T 1 respectively) are confirmed by time-resolved emission spectroscopy (TRES) and its extension, namely, time-resolved area normalized emission spectroscopy (TRANES). TRES provides useful information on the heterogeneity of the emissive species and the excited state kinetics.…”

“…Our exhaustive fluorometric studies suggest that the noteworthy observation of S 2 emission is observed for benzil and αnaphthil. 11,12 However, α-furil and 2,2′-pyridil do not show any emission from the higher excited state due to the energy proximity between the S 2 and S 1 states and thus the molecules can effortlessly move from the S 2 state to the S 1 state. 13,14 In the present work, we have performed exhaustive spectroscopic studies of another 1,2-dicarbonyl compound, namely, anthril, in both polar and nonpolar solvents at room temperature and liquid nitrogen temperature (77 K) to assign the multiple emissions.…”

“…The photophysical investigations of anthril in ethanol and methylcyclohexane have been performed in room temperature solution phases and cryogenic temperature glassy matrixes to explore the multiple emissions originating from the singlet and triplet states. For the assignment of the fluorescence and phosphorescence emission bands of the fluorophore, we have selected different time windows (depending on the fluorescence and phosphorescence lifetimes) at 77 K frozen matrixes to segregate both these bands precisely. − , Importantly, coexistence of the two isomeric fluorescences and phosphorescences from the same electronic states (S 1 and T 1 respectively) are confirmed by time-resolved emission spectroscopy (TRES) and its extension, namely, time-resolved area normalized emission spectroscopy (TRANES). TRES provides useful information on the heterogeneity of the emissive species and the excited state kinetics. , However, TRANES is a rather novel and model-free technique as developed by Periasamy et al and is exploited for the analysis of extrinsic and intrinsic fluorophores in chemical and biophysical systems. , A unique and valuable feature of TRANES is the possible observation of an isoemissive point in the spectra, signifying the coexistence of the two (and only two) emitting species in the emission spectra of the probe. − Quantum chemical calculations of anthril have also been performed by using density functional theory (DFT) and time dependent density functional theory (TDDFT) to construct the potential energy curves (PECs) in different ground and excited electronic states.…”