Does PRODAN Possess an O-TICT Excited State? Synthesis and Properties of Two Constrained Derivatives

Abstract

The synthesis and photophysical properties of 7-(dimethylamino)-3,4-dihydrophenanthren-1(2H)-one (7) and 3-(dimethylamino)-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalen-7-one (8) are reported. These compounds possess a cycloalkanone substructure that controls the extent of twisting of the carbonyl group. The six-membered ring in 7 forces the carbonyl group to be coplanar with the naphthalene ring, whereas the seven-membered ring in 8 induces a significant twist. Both have the substructure of PRODAN (6-propionyl-2-(dimethylamino)naphthalene, 1).Comparing the photophysical behavior of these compounds with that of PRODAN and 2,2-dimethyl-1-(4-methyl-1,2,3,4-tetrahydrobenzo[f]quinolin-8-yl)propan-1-one (3) indicates that PRODAN likely emits from a PICT excited state rather than from an O-TICT excited state.

Spectral properties of BADAN in solutions with different polarities

“…The fluorescence of these dyes has dual character and is described in terms of locally excited state and charge-transfer state in polar solvents [24][25][26][27][28]. There is no single vision of charge-transfer state conformation among researchers: in some works it was suggested that planar molecule fluoresces, while in other it was suggested that non-planar [27,[29][30][31][32][33][34][35][36][37][38].…”

Quantitative Design of Bright Fluorophores and AIEgens by the Accurate Prediction of Twisted Intramolecular Charge Transfer (TICT)

“…However, the TICT state was considered as an inconsequential artifact by some researchers . By investigating PRODAN derivatives whose dimethylamino or propionyl functional groups have been fixed in co‐planar orientation using alkylation (Figure a), several experimental studies have confirmed that the fluorescence of PRODAN originates from the LE/ICT state or LE states with charge transfer character (the planar conformation). However, it is noted that PRODAN displayed sub‐optimal quantum yields in polar solvents like water .…”

“…Nevertheless, their suboptimal and comparable quantum yields in the water–glycerol mixture (volume fractions=2/8) also validates the presence of hydrogen bond quenching (HBQ) phenomenon in PRODAN, as pointed out in previous studies . Indeed, as we changed the solvent to DMSO for avoiding hydrogen bond interactions around the oxygen atoms, the quantum yields of both P2 and P4 increased substantially (Supporting Information, Table S2).…”

Dual-Sensor Fluorescent Probes of Surfactant-Induced Unfolding of Human Serum Albumin

“…43,44 The correlation between the degree of quenching in an alcohol solvent, defined as log(I max /I), and Catalán’s solvent acidity parameter SA 41,45,46 is very linear. As such, the fluorescence intensity of these compounds can be used as sensors of H-bonding ability.…”