Solvent Influences on the Photophysics of Naphthalene:  Fluorescence and Triplet State Properties in Aqueous Solutions and in Cyclodextrin Complexes

Abstract

The photophysical properties of naphthalene were studied in aqueous solution (H2O and D2O), in some organic solvents (ethanol, hexane, and acetonitrile), and in complexes with the cyclodextrins (CDs) α-CD and β-CD, by means of absorption, steady-state and time-resolved fluorescence, circular dichroism, and triplet−triplet absorption spectroscopies. The structures of the CD inclusion complexes were computed using a dynamic Monte Carlo method. The main difference of the photophysics in the pure aqueous with respect to the organic media consists in a reduction of the fluorescence lifetime, τF, by a factor of about 2.5. Consideration of the triplet properties in aqueous and organic media led to the conclusion that this effect is most probably due to a corresponding increase of the intersystem crossing rate, induced by H2O or D2O. Inclusion of naphthalene in the CD hosts has the effect, at high CD concentration (>0.01 M), of increasing τF with respect to the aqueous medium, the value in α-CD being near to that in the organic media and the value in β-CD intermediate. The spectral and kinetic data are consistent with the predominant formation of 1:2 host:guest complexes with α-CD, and of 1:1 complexes with β-CD, although 2:2 complexes with β-CD are also formed and are identified by their excimer like fluorescence. Several experimental results, including the values of τF, and the temperature dependences of fluorescence and triplet−triplet absorption spectra on one hand and of triplet quenching and triplet−triplet annihilation kinetics on the other, point to a considerable structural flexibility of the 1:2 complex with α-CD.

Photophysical characterization of the plant growth regulator 2-(1-naphthyl) acetamide

“…The absorption band with maximum around 420 nm can be assigned to the NAD triplet-triplet absorption, and is in good agreement to that seen for triplet states of naphthalene and derivatives [10,21,47]. To confirm this assumption, and since it is well known that molecular oxygen is a strong quencher of triplet excited states of aromatic molecules, solutions of NAD in all solvents were excited at 266 nm as function of oxygen concentration.…”

“…Changing solvent polarity and hydrogen bond ability with these systems has been shown to lead to shifts in electronic absorption and luminescence spectra [15][16][17][18][19][20]. In addition, although more limited information is available, they may also cause changes in triplet excited state behavior [21,22]. We have recently reported a detailed study of the photodegradation of NAD, both under UV light and simulated solar irradiation conditions [23], including identification of major degradation products and toxicity studies.…”

Controllable Nanocage Structure Derived from Cyclodextrin-Intercalated Layered Double Hydroxides and Its Inclusion Properties for Dodecylbenzene

“…[35][36][37][38][39] To gain a clearer insight into the significance of the various effects of the surroundings, the fluorescence and absorption spectra of DDB in solvents of different dielectric constants and of DDB after inclusion in unsubstituted CD and CMCD in water/ethanol solution were recorded. Figure S7 (Supporting Information) shows the emission spectra of DDB in n-hexane, ethanol, N,N-dimethylformamide (DMF), and formamide and of DDB included in CD and CMCD in water/ ethanol solution.…”

Magnetic‐Field Effects in Organic Semiconducting Materials and Devices

“…The light emission from the singlet excitons generated from TTA is named delayed fluorescence. [33][34][35] In addition, the TTA must satisfy both spin momentum and energy conservation requirements. In general, there are two particular processes involved in TTA in organic materials: Figure 3.…”