Photophysics of 1-aminonaphthalenes

Abstract

We have investigated the photophysics of 1-aminonaphthalene and NN'-dimethyl-1aminonaphthalene in a variety of solvents. We find that the red shift of the emission spectrum, which is observed in polar solvents, is a consequence of two relaxation mechanisms. The first is an intramolecular reorganisation of the amino substituent that is stabilised by quite small changes in the solutes environment. The second, which is only observed when the solvent is moderately fluid, is a bulk relaxation of the solvent dipoles about the solutes excited-state dipole moment. A combination of these two effects results in a fluorescent state that has significant charge-transfer character. The nature of this state and the relationship between our observations and those made on more complex aminonaphthalene derivatives are discussed.

Supersonic beam investigations of indole and indole–halomethane complexes: intermolecular interactions

“…We are unaware of any solution phase lifetime measurements of unsubstituted indole in dichloromethane or chloroform and therefore cannot make any direct comparisons with our jet data. However, the values for these supersonic jet complexes are similar to those found (27) for indole in various other hydrogen bonding solvents (3-6 ns).…”

“…In this case there is minimal modification of the energy levels due to the weak nature of the intermolecular interactions. For stronger interactions such as hydrogen bonding other investigators have shown that one can expect rather large changes in the measured fluorescence lifetimes upon complexation (3,27).…”

Lower excited states of 7-azaindole dimer with a C2h(M) symmetry

“…This resemblance can reasonably be interpreted: If the LE state is considered, the excited molecule 7-AzI* is believed to be strongly perturbed by the counter molecule 7-AzI just like by the protic molecule/media (vide infra). Actually, this solvent effect is in close resemblance to the observation such as indoles [32] and 1-aminonaphthalenes [33], as well as in the acetonitrile solution of 1-methylindole [34]. Correspondingly, the S 1 state of the 7-AzI 2 in condensed phase (nonpolar media) can be regarded to be the (real) L a type LE state just as is the case of the nonreactive dimer (in contrast to that in the isolated condition), solvent perturbation being strong enough to prohibit immediate tunneling of back and forth, i.e., to destroy the C 2h (M) symmetry.…”

“…(It is considered that the electronic structure of the constituent molecule in the dimer is disturbed by the formation of the dimer like the monomer embedded in the polar media, even in the isolated condition.) It should also be noted that the lowest excited state of the molecules such as cited above in the polar solvent is sometimes named as a L a /CT state implying admixture of an intramolecular CT state and possibly of a charge-transfer-to-solvent (CTTS) state [32][33][34][35][36]. Similar effect may be involved in case of the dimer formation of 7-AzI not only in the condensed phase but also in the isolated condition, as will be discussed in the later publication [29].…”

A lifetime in photochemistry; some ultrafast measurements on singlet states

“…This was necessary because it was found that probes such as dansyl [23], and indoles [24,25] (which were models for tryptophan amino acid upon which many studies on proteins had been based), exhibited intrinsic complex decay functions, meaning that care had to be exercised in interpretation of fluorescence decay parameters in terms of biological phenomena alone [23][24][25][26][27][28][29]. Such complexities in fluorescence decays were also observed in molecules used as fluorescence standards, e.g.…”