Synthesis and Photophysical Properties of Models for Twisted PRODAN and Dimethylaminonaphthonitrile

Abstract

The synthesis and photophysical properties of 7-cyano-3,4-dihydro-2H-1,4-ethano-benzo[g]quinoline and 3,4-dihydro-2H-1,4-ethano-7-propionyl-benzo[g]quinoline are reported. These compounds possess a quinuclidine substructure that locks the tertiary amino group perpendicular to the naphthalene ring. Their excited states are models for the twisted excited states of 2-(dimethylamino)-6-naphthonitrile (DMANN) and 6-propionyl-2-(dimethylamino)naphthlene (PRODAN). In contrast to DMANN and PRODAN, the fluorescence of these twisted derivatives is strongly deactivated in polar solvents. Neither DMANN nor PRODAN likely emit from TICT excited states.

Spectral Heterogeneity of PRODAN Fluorescence in Isotropic Solvents Revealed by Multivariate Photokinetic Analysis

“…20 Most importantly, Abelt and his coworkers synthesized constrained PRODAN derivatives that definitively establish the planarity of the charge transfer state. 21,22 While their work has not eliminated all discussion of the viability of the "twisted excited state" explanation, 23 the spectra emitted by the constrained twisted derivative indicate a minor, if any, role for a twisted excited state in PRODAN photokinetics. In fact, the most recent theoretical calculations support assigning PRODAN emission in homogeneous solvents to a planar excited state.…”

Novel nonplanar triphenylamine-centered oligofluorenes: Synthesis, thermal, photophysical and electrochemical properties

“…upon excitation in such solvent. The two peaks of the dual fluorescence are generally assigned to the locally excited (LE) state of the molecule and the twisted intramolecular charge transfer (TICT) species formed in the excited state, respectively [23][24][25]. Spectroscopic analysis reveals that in TCM, the mission spectrum of 6 is dominated by its TICT emission, which indicates that a strong ICT occurs even in weak polar solvent.…”

Coherent nuclear wave packet dynamics of laurdan launched by intramolecular charge transfer

“…Laurdan, an analogue of DMABN (4-dimethylaminobenzonitrile), which is the benchmark system of ICT reaction, consists of an electron-donating dimethylamino group and an electron-withdrawing carbonyl group on the opposite side of the naphthalene. The ICT reaction may proceed through the twisting of the dimethylamino group, although its dynamics including the structural change still remains under intense investigation because of the conflicting experimental and theoretical reports [3,4].…”