Journal of Photochemistry and Photobiology A: Chemistry 183 (2006) 165–170
Solvent effect on the photophysical properties of
4-phenoxy-N-methyl-1,8-naphthalimide
J.L. Magalh˜ aes, R.V. Pereira, E.R. Triboni, P. Berci Filho,
M.H. Gehlen, F.C. Nart
∗
Instituto de Qu´ ımica de S ˜ ao Carlos, Universidade de S ˜ ao Paulo, Caixa Postal 780,
13560-590 S ˜ ao Carlos, SP, Brazil
Received 2 December 2005; received in revised form 10 February 2006; accepted 8 March 2006
Available online 18 April 2006
Abstract
The photophysical properties of N-methyl-1,8-naphthalimide (NI) and 4-phenoxy-N-methyl-1,8-naphthalimide (4-PNI) are studied by steady-
state and time-resolved emission measurements. Both absorption and fluorescence spectra are red-shifted when the electron donor phenoxy group
(–OPh) is introduced at the C-4 position. Compared to NI, the spectral shift in acetonitrile is 27 and 42 nm for the absorption and fluorescence,
respectively. The 4-PNI shows high fluorescence emission in non-polar aprotic solvents that can be ascribed to stabilization of the S
1
state. The
emission intensity of the 4-PNI decreases by addition of water to dioxane solution, and the fluorescence quenching occurs by combination of
dynamic and static contribution ascribed to specific solute–solvent interaction.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Naphthalimide; Solvent effects; Photophysical properties
1. Introduction
Naphthalimides comprise a class of chromophore whose
electronic absorption and emission depend on the properties
of the surrounding medium. In general, non-substituted 1,8-
naphthalimides present low fluorescence quantum yield. These
trends have been explained by the fast intersystem crossing
from the excited –
*
singlet state to a close-lying n–
*
triplet
state, a mechanism which is particularly efficient in the case
of the 1,8-naphthalimide [1]. The photophysical behavior of
1,8-naphthalimide derivatives is a function of C-4 substitution.
Substitution of electron-donating groups usually increases the
fluorescence emission, particularly when alkoxy-groups at the
C-4 position are used. These alkoxy derivatives constitute a
very important class of compounds with intensive fluorescence
and very good photo-stability. Thus, they have a wide range of
∗
Corresponding author. Tel.: +5 16 3373 9926; fax: +5 16 33739952.
E-mail address: nart@iqsc.usp.br (F.C. Nart).
applications as organic dyes and luminophores [2], probes for
analytical purposes [3], fluorophore for optical chemosensing
[4] and liquid crystal displays [2]. Bojinov and Grabchev have
used 4-alkoxy-1,8-naphthalimide derivatives as fluorophores
for synthetic blue fluorescent polymers [5]. The spectroscopic
properties and molecular structure of naphthalimide derivatives
have been investigated and described in several publications
[6–8].
The ability of 1,8-naphthalimide derivatives to be very sensi-
tive to their surrounding render them as solvatochromic probes
where the effects of solvent polarity on the electronic emission
and absorption spectra are studied [9].
Since the literature has not yet reported any system-
atic study of aryl substitution at the C-4 position of 1-8-
naphthalimide, its seems to be opportune to detail the photo-
physics of the 4-phenoxy-N-methyl-1,8-naphthalimide (4-PNI)
compound, which was synthesized according the Scheme 1.
The photophysical properties of 4-PNI in different solvents
and in dioxane–water binary mixtures, and the role of probe-
solvent interaction, which modulates the intramolecular charge
transfer process of 4-PNI is investigated in this contribu-
tion.
1010-6030/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2006.03.012