Ground and excited state dipole moments of planar vs. twisted p-N,N-(dimethylamino)benzonitrile systems: maximum charge transfer for minimum overlap

1992 ◽  
Vol 70 (7) ◽  
pp. 1932-1938 ◽  
Author(s):  
Hemant K. Sinha ◽  
S. Muralidharan ◽  
Keith Yates
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Degrees Of Freedom ◽  
Theoretical Calculations ◽  
Dipole Moments ◽  
Torsional Angle ◽  
Dimethylamino Group ◽  
Maximum Charge ◽  
Donor Acceptor ◽  
Excited State Dipole Moments

Electric field induced change in the absorption spectrum (electrochromism) has been employed to obtain the ground and excited state dipole moments of planar and sterically hindered (twisted) p-N,N-(dimethylamino)benzonitriles in dioxane solution. These studies support the twisted intramolecular charge transfer (TICT) hypothesis and provide additional insight to the TICT concept. The charge transfer nature of the excited state has been found to directly depend on the torsional angle of the N,N-dimethylamino group with respect to the benzonitrile moiety. It is suggested that solvent coupling is essential to initiate twisting by affecting the intramolecular degrees of freedom and the existence of the highly dipolar excited state is a result of such twisting of the donor–acceptor bond. Theoretical calculations have been performed to explain the observed changes in dipole moment values.

Excited state dipole moments and polarizabilities of some aromatic alkenes and alkynes

1990 ◽  
Vol 68 (9) ◽  
pp. 1507-1513 ◽  
Author(s):  
Hemant K. Sinha ◽  
Paul C. P. Thomson ◽  
Keith Yates
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Excited States ◽  
Experimental Error ◽  
Acid Catalysis ◽  
Dipole Moments ◽  
Excited State Dipole Moments ◽  
Induced Changes ◽  
Excited State Dipole Moment ◽  
Shed Light

Electric field induced changes in the optical absorption spectra (electrochromism) have been used to obtain the excited state dipole moments and polarizabilities of styrene, 2-vinylnaphthalene, 2-naphthylacetylene, and 9-vinylanthracene. Excited state dipole moments of the order of 4–6 debye have been obtained for all these molecules except for 9-vinylanthracene, for which the excited state dipole moment is zero within experimental error. These results support earlier proposals of the involvement of charge transfer excited states in the fast and efficient acid-catalysed photohydration reactions of this type of substrate. 9-Vinylanthracene, on the other hand, under similar conditions reacts differently to give a dimer as the major photoproduct, and its reaction is not subject to acid catalysis. These results shed light on the importance of charge transfer excited states on the efficiency of photohydration reactions. Keywords: electrochromism, excited state, dipole moments, polarizabilities.

Charge-Transfer Properties of Dye-Sensitized Solar Cells via Long-Range-Corrected Density Functional Theory

2008 ◽  
Vol 1120 ◽  
Author(s):  
Bryan Matthew Wong
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Charge Transfer ◽  
Solar Cell ◽  
Long Range ◽  
Density Functional ◽  
Dipole Moments ◽  
Excitation Energies ◽  
Functional Theory ◽  
Excited State Dipole Moments

AbstractThe excited-state properties in a series of solar cell dyes are investigated with a long-range-corrected (LC) functional which provides a more accurate description of charge-transfer states. Using time-dependent density functional theory (TDDFT), the LC formalism correctly predicts a large increase in the excited-state electric dipole moment of the dyes with respect to that of the ground state, indicating a sizable charge separation associated with the S1 ← S0 excitation. The performance of the LC-TDDFT formalism, illustrated by computing excitation energies, oscillator strengths, and excited-state dipole moments, demonstrates that the LC technique provides a consistent picture of charge-transfer excitations as a function of molecular size. In contrast, the widely-used B3LYP functional severely overestimates excited-state dipole moments and underestimates the experimentally observed excitations, especially for larger dye molecules. The results of the present study emphasize the importance of long-range exchange corrections in TDDFT for investigating the charge-transfer dynamics in solar cell dyes.

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