Excited-State Conformational/Electronic Responses of Saddle-ShapedN,N′-Disubstituted-Dihydrodibenzo[a,c]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination

Abstract

A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N'-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N'-dimethyl), DPAC (N,N'-diphenyl), and FlPAC (N-phenyl-N'-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N'-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N'-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N'-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N'-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and even to white light generation upon optimization of the surrounding media.

A soluble cryogenic thermometer with high sensitivity based on excited-state configuration transformations

“…27 For its high boiling point (353 K) and low melting point (137 K), the chemically stable liquid MeTHF was chosen as a medium for FIPAC to perform the temperature-dependent experiment. 27 For its high boiling point (353 K) and low melting point (137 K), the chemically stable liquid MeTHF was chosen as a medium for FIPAC to perform the temperature-dependent experiment.…”

“…4 (a) Absorption of FIPAC in MeTHF between 138 K and 343 K. (b) The emission spectra of FIPAC in MeTHF between 138 K and 343 K (excitation wavelength 370 nm). 27 This low energy barrier lays the foundation for applying this system in the cryogenic temperature detection field for which the excited-state configuration transformations could occur at very low temperature. 33,34 Hence, the energy barrier was calculated to be DE = 0.08279 eV (see ESI †).…”

“…27 High viscosity will prevent excited-state configuration transformations, which will lead to viscosity-dependent PL. 27 High viscosity will prevent excited-state configuration transformations, which will lead to viscosity-dependent PL.…”

“…27 High viscosity will prevent excited-state configuration transformations, which will lead to viscosity-dependent PL. 27 Therefore, further experiments are needed to apply this FIPAC system in the detection of viscosity. 9 However, in contrast to the energy control in temperaturedependent PL, the influence of viscosity on PL is timedependent.…”

A Dual‐Stimuli‐Responsive Coordination Network Featuring Reversible Wide‐Range Luminescence‐Tuning Behavior

“…[4,5] Second, am inority of them exhibit am ultistimuli response in the form of individual events (e.g., conformational variation, [6] molecular alignment modulation, [7] crystal-to-amorphous transition [8][9][10] )characterized by aset of discrete luminescence peaks. [11] Herein, we report an intriguing stimuli-responsive coordination network, [Cd 3 (TPPA) 2 (NDA) 3 ]·(DMF) 10 ·(H 2 O) 6 (namely, NKU-121;T PPA: tri(4-(pyridine-4-yl)phenyl)amine,N DA :2 ,6-naphthalenedicarboxylic acid, DMF: N,Ndimethylformamide), which undergoes ag radual and reversible structural deformation under either thermal or pressure stimulation. [11] Herein, we report an intriguing stimuli-responsive coordination network, [Cd 3 (TPPA) 2 (NDA) 3 ]·(DMF) 10 ·(H 2 O) 6 (namely, NKU-121;T PPA: tri(4-(pyridine-4-yl)phenyl)amine,N DA :2 ,6-naphthalenedicarboxylic acid, DMF: N,Ndimethylformamide), which undergoes ag radual and reversible structural deformation under either thermal or pressure stimulation.…”