Influences of protonation and hydrogen bonding on intramolecular charge transfer compounds possessing different spacers

Abstract

This work investigated the influence of protonation and hydrogen bonding on intramolecular charge transfer (ICT) through different spacers. Three compounds, DS-NH 2 (with a conjugated double bond), TS-NH 2 (with a conjugated triple bond), and SS-NH 2 (with a flexible saturated bond), possessing the same donor group (aniline) and the same acceptor group (naphthalene) but with different linkages were synthesized for this purpose. The double bond and triple bond spacers provided a more efficient ICT pathway than a flexible saturated bond in the ground state, so an ICT absorption band was observed for compounds DS-NH 2 and TS-NH 2. Although SS-NH 2 did not exhibit any ICT absorption band, two kinds of intramolecular exciplex emissions were observed depending on the solvent polarity. The excited-state dipole moment of DS-NH 2 is less than that of TS-NH 2. The ICT absorption and emission bands are quenched by protonation in this system. The influence of hydrogen bonding for DS-NH 2 and TS-NH 2 only occurs in the ground state and disappears in the excited state. The intermolecular hydrogen-bond between SS-NH 2 and CF 3CH 2OH molecules block the reorientation of the amino group and prevent the occurrence of the ICT. Therefore, no exciplex emission was recorded for SS-NH 2 in the mixed (CH 2Cl 2:CF 3CH 2OH) solvents.