Solvent-dependent dual fluorescence of the push–pull system 2-diethylamino-7-nitrofluorene

Abstract

The solvent-dependent excited state behavior of the molecular push-pull system 2-diethylamino-7-nitrofluorene has been explored using femtosecond transient absorption spectroscopy in combination with density functional theory calculations. Several excited state minima have been identified computationally, all possessing significant intramolecular charge transfer character. The experimentally observed dual fluorescence is suggested to arise from a planar excited state minimum and another minimum reached by twisting of the aryl-nitrogen bond of the amino group. The majority of the excited state population, however, undergo non-radiative transitions and potential excited state deactivation pathways are assessed in the computational investigation. A third excited state conformer, characterized by twisting around the aryl-nitrogen bond of the nitro group, is reasoned to be responsible for the majority of the non-radiative decays and a crossing between the excited state and ground state is localized. Additionally, ultrafast intersystem crossing is observed in the apolar solvent cyclohexane and rationalized to occur via an El-Sayed assisted transition from one of the identified excited state minima. The solvent thus determines more than just the fluorescence lifetime and shapes the potential energy landscape, thereby dictating the available excited state pathways.

Leveraging Coupled Solvatofluorochromism and Fluorescence Quenching in Nitrophenyl‐Containing Thiazolothiazoles for Efficient Organic Vapor Sensing

“…The potential for both a planarized and a twisted intramolecular charge transfer state (PLATICT) was explored due to the possibility of a twisted (amino‐carbon phenyl) bond in the excited state. [ 36,37 ] Rotating and fixing the TTz amino‐phenyl dihedral bond of Bu 2 N‐TTz‐NO 2 to 90° (Figure S44, Supporting Information), and modeling the absorbance spectra provided a good fit of the experimental absorbance and emission spectra ( Figure c). This is strong evidence for the TTz dyes to be in a twisted ground state.…”

“…Excited states were modeled in Gaussian using a hybrid functional PBE0 (PBE1PBE) with a 6-311+G(d,p) basis set and integral equation formalism model (IEFPCM) for solvation. [36,[46][47] Initial optimization of the TTz derivatives in a vacuum demonstrates the push-pull nature of the molecules with HOMOs residing on the aminophenyl donating groups, and LUMOs on the nitrophenyl groups (Figures S41-S43, Supporting Information). To observe both SWB and LWB bands, Bu 2 N-TTz-NO 2 was modeled in chlorobenzene (ClBz), however, time-dependent DFT (TDDFT) calculations did not properly reflect the experimental absorbance spectra (Figure S48, Supporting Information).…”

Selective Modification for Red‐Shifted Excitability: A Small Change in Structure, a Huge Change in Photochemistry

“…Ap ublication by the Sølling group, [28] who examined the dual fluorescenceo fasimilarc ore structure, 2-diethylamino-7nitrofluorene, can be used for comparison. They computationally identifieds everale xcited state minima with CT character, including aP -ICT state, as well as rotation aroundt he amino group (T-ICT) and also the nitro group, which accounts for the majority of the non-radiative decay.T hey observed complex solventd ependence and ultrafast ISC in somec ases (e.g., apolar cyclohexane), which results then in one single fluorescent transition.…”

Nonstatistical Photoinduced Processes in Gaseous Organic Molecules

“…The sun is incoherent and systems in solution are incoherent. As much as we have tried to transfer some of the gas phase consideration to problems in the condensed phase, − there is still a significant amount of work to be done to fully understand the nonstatistical and directionality aspects of solution-phase problems. The same appears to link processes that are induced by a femtosecond laser pulse and those that have their offspring in excitation by incoherent CW sources such as the sun.…”