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The infrared spectra of the hydrogen bonded solute-solvent complexes in electronically excited states are calculated to study the early time hydrogen-bonding dynamics of chromophore in hydrogen-donating solvents upon photoexcitation by using the time-dependent density functional theory method. It demonstrated that the intermolecular hydrogen bonds between coumarin 102 (C102) and hydrogen donating solvents are strengthened in the early time photoexcitation to the electronically excited state by theoretically monitoring the stretching models of C=O and H-O groups.

The ultrafast hydrogen bond strengthening of the photoexcited fluorenone (FN) in various hydrogen donating alcohol solvents is studied. The results demonstrate that hydrogen bonding can easily quench the total fluorescence of fluorenone in polar protic solvents.

The solute-solvent intermolecular photoinduced transfer (ET) reaction which account for the drastic fluorescence quenching behaviors of oxazine 750 (OX750) chromophore in protic alcoholic solvents is reported.

The photosynthetic purple bacterium Thermochromatium (Tch.)tepidumis a thermophile that grows at an optimal temperatureof ∼50 °C. We have investigated, by means of steady-stateand time-resolved optical spectroscopies, the effects of temperatureon the near-infrared light absorption and the excitation energy transfer(EET) dynamics of its light-harvesting complex 2 (LH2), for whichthe mesophilic counterpart of Rhodobacter(Rba.) sphaeroides2.4.1 (∼30 °C)was examined in comparison. In a limited range around the physiologicaltemperature (10–55 °C), the B800-to-B850 EET process ofthe Tch. tepidumLH2, but not the Rba. sphaeroidesLH2, was found to be characteristically temperature-dependent, mainlybecause of a temperature-tunable spectral overlap. At 55 °C,the LH2 complex from Tch. tepidummaintained efficientnear-infrared light harvesting and B800-to-B850 EET dynamics, whereasthis EET process was disrupted in the case of Rba. sphaeroides2.4.1 owing to the structural distortion of the LH2 complex. Ourresults reveal a remarkable thermal adaptability of the light-harvestingfunction of Tch. tepidum, which could enhance ourunderstanding of the survival strategy of this thermophile in responseto environmental challenges. [ABSTRACT FROM AUTHOR]

In this work, spectroscopic techniques and quantum chemistry calculations were used to investigate the photophysical properties of various multinuclear platinum complexes with different conformational geometries. This suite of complexes includes a Pt–pyridyl square, a Pt–carboxylate triangle, and a mixed Pt–pyridyl–carboxylate rectangle, as well as two mononuclear Pt model complexes. Studying the individual molecular precursors in the context of larger assemblies is important to provide a complete understanding of the factors governing the observed photophysical properties of a given system. The absorption and emission bands of the parent linear dipyridyl donor (ligand 1) are largely preserved in the [4 + 4] square and the multicomponent [4 + 2 + 2] rectangle (3 and 4, respectively), with significant red shifts. The [3 + 3] Pt–carboxylate triangle containing p-phthalic acid is nonemissive. Phosphorescence and nanosecond transient spectroscopy on 3 and 4 reveal that the introduction of platinum atoms enhances spin–orbital coupling, thereby increasing the rate of intersystem crossing. This phenomenon is consistent with the low fluorescence quantum yields and short fluorescence lifetimes of 3 and 4. Moreover, the electronic structures for the ground state and low-lying excited states of these compounds were studied using quantum chemistry calculations. The fluorescent states of the platinum complexes are local excited states of ligand-centered π-π* transition features, whereas the nonfluorescent states are intramolecular charge-transfer states. These low-lying intramolecular charge-transfer states are responsible for the nonemissive nature of small molecules 1 and 2 and triangle 5. As the interactions between these components determine the properties of their corresponding assemblies, we establish novel excited-state decay mechanisms which dictate the observed spectra. [ABSTRACT FROM AUTHOR]

An investigation of a series of platinum-containing organometallic complexes for the study of fluorescence phenomena in organometallic chromophores controlled by the intramolecular charge transfer (ICT) is presented in this work. We report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the substituent effects on the ICT and fluorescence emission. We demonstrate that the fluorescence maximum and lifetimes greatly depend on different substituents and the presence of bimetallic platinum donor. This work paves the way for an understanding of the fluorescence phenomena controlled by molecular ICT characters of these kinds of platinum-containing organometallic complexes. [ABSTRACT FROM AUTHOR]

To study the early time hydrogen-bonding dynamics of chromophore in hydrogen-donating solvents upon photoexcitation, the infrared spectra of the hydrogen-bonded solute−solvent complexes in electronically excited states have been calculated using the time-dependent density functional theory (TDDFT) method. The hydrogen-bonding dynamics in electronically excited states can be widely monitored by the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds. In this study, we have demonstrated that the intermolecular hydrogen bonds between coumarin 102 (C102) and hydrogen-donating solvents are strengthened in the early time of photoexcitation to the electronically excited state by theoretically monitoring the stretching modes of CO and H−O groups. This is significantly contrasted with the ultrafast hydrogen bond cleavage taking place within a 200-fs time scale upon electronic excitation, proposed in many femtosecond time-resolved vibrational spectroscopy experiments. The transient hydrogen bond strengthening behaviors in excited states of chromophores in hydrogen-donating solvents, which we have demonstrated here for the first time, may take place widely in many other systems in solution and are very important to explain the fluorescence-quenching phenomena associated with some radiationless deactivation processes, for example, the ultrafast solute−solvent intermolecular electron transfer and the internal conversion process from the fluorescent state to the ground state. [ABSTRACT FROM AUTHOR]