“…In the HOMO (the highest π orbital), the charge distribution is mainly localized on the N−H group, while in the LUMO (the lowest π* orbital), the electron density is substantially large at the CO group. Therefore, the lowest π* ← π transition of the AD molecule is of intramolecular charge-transfer type from the N−H group to the CO group. , The drastic change of the charge distribution in the HOMO and LUMO provides the spectral shifts characteristic to the solvent numbers and the cluster conformations as follows. 8 Spectral shifts in the 1 (π,π*) transition of AD−(H 2 O) n ( n = 1−5) plotted against the number of water molecules.…”
Section: Characterization Of Solvent Geometry Via Spectral
Shiftsmentioning
confidence: 99%
“…Therefore, the lowest π* r π transition of the AD molecule is of intramolecular charge-transfer type from the N-H group to the CdO group. 35,42 The drastic change of the charge distribution in the HOMO and LUMO provides the spectral shifts characteristic to the solvent numbers and the cluster conformations as follows.…”
Section: Characterization Of Solvent Geometry Via Spectral Shiftsmentioning
confidence: 99%
“…First, remarkable solvation effects (H-bonding effects) on nonradiative processes in AD have been identified in liquid solution. ,− Accumulated knowledge of its electronic-energy levels and fluorescence properties in various solvents should be valuable for detailed comparison with results of the clusters. Second, AD is a planar rigid molecule with C 2 v symmetry . Owing to the rigidity of the system, any experimentally measured kinetics can be assigned to photophysical processes, and not to significant changes of structure in the excited state or photochemical processes.…”
Section: Introductionmentioning
confidence: 99%
“…Second, AD is a planar rigid molecule with C 2V symmetry. 35 Owing to the rigidity of the system, any experimentally measured kinetics can be assigned to photophysical processes, and not to significant changes of structure in the excited state or photochemical processes. Last, AD has multiple H-bonding sites, i.e., CdO, N-H, and π-aromatic rings, thus it is particularly suitable for investigating site-specificity in solvation (H-bonding) effects on nonradiative dynamics.…”
A series of papers (I-III) reports spectroscopic investigation on structure and dynamics of 9(10H)-acridone (AD) and its hydrated clusters. As the first part of the series, the present paper describes their lowest 1 (π,π*) electronic transition in the 370-400 nm region studied by fluorescence-based laser spectroscopy and massselective two-color resonance-enhanced two-photon ionization (2C-R2PI). Thirteen fluorescent hydrates as well as the monomer have been identified in fluorescence-excitation and UV-UV hole-burning measurements, and size assignments for relatively smaller clusters, AD-(H 2 O) n (n ) 1-6), have been conducted by 2C-R2PI. The origin bands for larger-size clusters show larger red shifts converging at ca. 2200 cm -1 but the changes are nonmonotonic, with a substantial increase from n ) 2 to 3. Density-functional-theory (DFT) calculations at the B3LYP/6-31G(d,p) level have predicted that the energy difference between the CdO and N-H bonded isomers is quite small (only ≈ 1 kcal/mol) for n ) 1 and 2. The observed spectral shifts of fluorescent hydrates with n ) 1 and 2 are well reproduced by the HOMO-LUMO gap in the DFT orbital energies of either of the N-H or CdO bonded isomers, leaving the definitive structural assignments to fluorescence-detected infrared spectroscopy which will be described in paper II. For the larger clusters (n ) 3-5), several minimum-energy structures have been identified within 2 kcal/mol in binding energy, among which the conformers with water molecules bridging between the CdO and N-H sites over the AD's aromatic rings are identified as the observed species, based on good agreement between the calculated and observed spectral shifts.
“…In the HOMO (the highest π orbital), the charge distribution is mainly localized on the N−H group, while in the LUMO (the lowest π* orbital), the electron density is substantially large at the CO group. Therefore, the lowest π* ← π transition of the AD molecule is of intramolecular charge-transfer type from the N−H group to the CO group. , The drastic change of the charge distribution in the HOMO and LUMO provides the spectral shifts characteristic to the solvent numbers and the cluster conformations as follows. 8 Spectral shifts in the 1 (π,π*) transition of AD−(H 2 O) n ( n = 1−5) plotted against the number of water molecules.…”
Section: Characterization Of Solvent Geometry Via Spectral
Shiftsmentioning
confidence: 99%
“…Therefore, the lowest π* r π transition of the AD molecule is of intramolecular charge-transfer type from the N-H group to the CdO group. 35,42 The drastic change of the charge distribution in the HOMO and LUMO provides the spectral shifts characteristic to the solvent numbers and the cluster conformations as follows.…”
Section: Characterization Of Solvent Geometry Via Spectral Shiftsmentioning
confidence: 99%
“…First, remarkable solvation effects (H-bonding effects) on nonradiative processes in AD have been identified in liquid solution. ,− Accumulated knowledge of its electronic-energy levels and fluorescence properties in various solvents should be valuable for detailed comparison with results of the clusters. Second, AD is a planar rigid molecule with C 2 v symmetry . Owing to the rigidity of the system, any experimentally measured kinetics can be assigned to photophysical processes, and not to significant changes of structure in the excited state or photochemical processes.…”
Section: Introductionmentioning
confidence: 99%
“…Second, AD is a planar rigid molecule with C 2V symmetry. 35 Owing to the rigidity of the system, any experimentally measured kinetics can be assigned to photophysical processes, and not to significant changes of structure in the excited state or photochemical processes. Last, AD has multiple H-bonding sites, i.e., CdO, N-H, and π-aromatic rings, thus it is particularly suitable for investigating site-specificity in solvation (H-bonding) effects on nonradiative dynamics.…”
A series of papers (I-III) reports spectroscopic investigation on structure and dynamics of 9(10H)-acridone (AD) and its hydrated clusters. As the first part of the series, the present paper describes their lowest 1 (π,π*) electronic transition in the 370-400 nm region studied by fluorescence-based laser spectroscopy and massselective two-color resonance-enhanced two-photon ionization (2C-R2PI). Thirteen fluorescent hydrates as well as the monomer have been identified in fluorescence-excitation and UV-UV hole-burning measurements, and size assignments for relatively smaller clusters, AD-(H 2 O) n (n ) 1-6), have been conducted by 2C-R2PI. The origin bands for larger-size clusters show larger red shifts converging at ca. 2200 cm -1 but the changes are nonmonotonic, with a substantial increase from n ) 2 to 3. Density-functional-theory (DFT) calculations at the B3LYP/6-31G(d,p) level have predicted that the energy difference between the CdO and N-H bonded isomers is quite small (only ≈ 1 kcal/mol) for n ) 1 and 2. The observed spectral shifts of fluorescent hydrates with n ) 1 and 2 are well reproduced by the HOMO-LUMO gap in the DFT orbital energies of either of the N-H or CdO bonded isomers, leaving the definitive structural assignments to fluorescence-detected infrared spectroscopy which will be described in paper II. For the larger clusters (n ) 3-5), several minimum-energy structures have been identified within 2 kcal/mol in binding energy, among which the conformers with water molecules bridging between the CdO and N-H sites over the AD's aromatic rings are identified as the observed species, based on good agreement between the calculated and observed spectral shifts.
A formula is derived for the emission anisotropy r(β, Rs) of a polymer film as a function of the stretch ratio Rs of the film and of the angle β between the absorbing and emitting oscillators for the case when the long axis of the molecule makes an angle φ = 90° with the absorbing oscillator. This relation is verified, together with that obtained previously for φ = 0°, on the example of acridone and anthracene in polyvinyl alcohol. The experimental results obtained for r(β, Rs) as a function of Rs confirm the character of the predicted theoretical curves. The reasons for the lack of quantitative agreement is also discussed.
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