The Effect of Acceptor Group Variation on the Solvatochromism of Donor‐acceptor Fluorophores

Abstract

The absorption and emission characteristics of five hydroxytetrahydrochrysenes substituted with acceptor groups (nitro, cyano, methylketone, 1 degree amide and methyl ester) (THC-NO2, THC-CN, THC-COCH3, THC-CONH2 and THC-CO2CH3, respectively) were investigated in an extensive set of solvents. The order of absorption and fluorescence bathochromicity are: THC-NO2 > THC-COCH3 > THC-CN > or = THC-CO2CH3 > THC-CONH2 and THC-NO2 >> THC-COCH3 > THC-CO2CH3 > THC-CN > THC-CONH2, respectively. The emission spectra of these compounds are sensitive to the solvent polarity (ET[30] scale) in the order: THC-NO2 > THC-COCH3 > THC-CO2CH3 > THC-CONH2 > THC-CN. The response of the emission maxima of these compounds to the solvent polarity and hydrogen-bond donor/acceptor properties (pi */alpha/beta and acity/basity scales) was also determined. The emission energies of THC-NO2 were most sensitive to pi *, beta, acity, and basity of the solvent; those of the amide were least sensitive to the solvent pi *, beta, and basity. The ground- and excited-state dipole moments were determined by semiempirical molecular orbital calculations and the absorption/fluorescence solvent-shift method, respectively. THC-NO2 had the largest ground- and excited-state moments. The ester and amide had the smallest ground- and excited-state moments, respectively. In general, unsatisfactory results were obtained for correlations of the emission and absorption energies, fluorescence solvatochromism and the ground- and excited-state dipole moments with the Hammett substituent constants of the five acceptor groups. Acceptable correlations were obtained for the absorption and emission energies and the fluorescence solvatochromism with the substituent constants if the cyano compound was excluded.

Signaling Recognition Events with Fluorescent Sensors and Switches

“…Red-shifted fluorescence induced by polar solvents can be observed to evolve over a few picoseconds following excitation due to the rotational relaxation of solvent molecules around the fluorophore mentioned above. , Hydrogen bonding can also contribute to the situation . Many of the better performers in this category are π-electron systems with push−pull substituent pairs, e.g., 14 , 15 , and 16 , bimanes, diarylalkenes, and furocoumarins are further sets of examples.…”

“…Even pyrene-1-carboxaldehyde fits this category (even though it is monosubstituted) provided that protic solvents are used to avoid low-lying nπ* excited states . Several of these cases give rise to linear solvation energy relationships of emission maximum wavenumber versus Kamlet−Taft solvent parameters. ,, Other solvent properties can also serve as independent variables. −

4 Solvent effect on absorption spectral wavelength for a fluorophore with an ICT excited state. FC represents a Franck−Condon excited state.

…”

“…158 Many of the better performers in this category are π-electron systems with push-pull substituent pairs, e.g., 14, 159 15, 160 and 16. 161 Aminophthalimides, 152,153 bimanes, 162 diarylalkenes, 163 and furocoumarins 164 are further sets of examples. Even pyrene-1-carboxaldehyde fits this category (even though it is monosubstituted) provided that protic solvents are used to avoid low-lying nπ* excited states.…”

“…56 Several of these cases give rise to linear solvation energy relationships of emission maximum wavenumber versus Kamlet-Taft solvent parameters. 161,163,164 Other solvent properties can also serve as independent variables. [165][166][167] Some fluorescent ICT sensors can report on two quasi-independent microenvironmental parameters by means of two fluorescence spectral parameters.…”

A New Series of Proton/Charge Transfer Molecules: Synthesis and Spectral Studies of 2-(5-Aryl-1-carbomethoxy-1H-pyrazol-3-yl)phenols

“…Due to negligible reabsorption, these molecules are potential candidates for use in practical applications such as laser dyes (12.18-21), special Raman filters (22), switches for dye laser pulse shortening (23) and hardscintillator counters (24). Another interesting application is using ESIPT or ESICT molecules as fluorescence probes to investigate a variety of biological environments such as a protein's binding site (25)(26)(27)(28)(29)(30). Recently, Catalan et al have also looked at N-(2'-hydroxyphenyl)pyrazoles that undergo ESIPT and their ability to photoprotect polystyrene (5,6).…”