Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.

The dynamics of the excited states of 3- and 4-aminofluoren-9-ones (3AF and 4AF, respectively) are investigated in different kinds of solvents by using a subpicosecond time-resolved absorption spectroscopic technique. They undergo hydrogen-bonding interaction with protic solvents in both the ground and excited states. However, this interaction is more significant in the lowest excited singlet (S(1)) state because of its substantial intramolecular charge-transfer character. Significant differences in the spectroscopic characteristics and temporal dynamics of the S(1) states of 3AF and 4AF in aprotic and protic solvents reveal that the intermolecular hydrogen-bonding interaction between the S(1) state and protic solvents plays an important role in its relaxation process. Perfect linear correlation between the relaxation times of the S(1) state and the longitudinal relaxation times (tau(L)) of alcoholic solvents confirms the prediction regarding the solvation process via hydrogen-bond reorganization. In the case of weakly interacting systems, the relaxation process can be well described by a dipolar solvation-like process involving rotation of the OH groups of the alcoholic solvents, whereas in solvents having a strong hydrogen-bond-donating ability, for example, methanol and trifluoroethanol, it involves the conversion of the non-hydrogen-bonded form to the hydrogen-bonded complex of the S(1) state. Efficient radiationless deactivation of the S(1) state of the aminofluorenones by protic solvents is successfully explained by the energy-gap law, by using the energy of the fully solvated S(1) state determined from the time-resolved spectroscopic data.

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Background: Oral submucous fibrosis (OSMF) is a doubtlessly malignant disorder of the oral cavity. The surgical control of this situation involves excision of the fibrotic bands and interpositional grafts to keep the elevated oral opening. Various strategies and graft had been utilized with differing achievement rates. Aims and Objective: Through this study, an attempt was made to evaluate the efficacy of collagen membrane as wound dressing material for mucosal defect in oral submucous fibrosis. Materials and Methods: The study include 30 patients in the age group of 15 to 60 years with stage III or IVa of oral sub mucous fibrosis all of which underwent operation under general anesthesia to enhance their mouthopening by fibrotomy of bands and placement of collagen membrane by same surgeon. After surgery all the patients were accessed under parameter like hemostatic effect, pain relief, granulation tissue formation, epithelization, contracture and reactivity. All patients were given similar prescriptions for pain killer, antibiotics and postoperative instructions. All patients were examined postoperatively. Results: In this study various parameter were accessing the efficacy of collagen membrane on wound defects were recorded. In this 1st parameter hemostatic 28 patients had a score of good (93.3%) with bleeding stopping within 5 minutes after application of membrane and only 2 patients had a score of fair (6.66%). In pain relief analgesics were stopped on the day of 3rd after procedure 16 patients had a good (53.3%) score, 12 patients had a fair (40%) score while only 2 patients gad a poor (6.66%) score. All the patients had sufficient granulation tissue formation of entire wound therefore all the patients had score of good (100%) at the end of two weeks. Epithelization was noted in 28 patients who had score of good (93.3%) after 1 month. Contracture of the wound site at the end of 3 months were noted and rated as good in 20 patients (66.6%) while fair (33.3%) in 10 patients. No reactivity of any form was found in any of the subjects (100%). Conclusion: In our study we noticed that collagen membrane was found to be very effective in all the subjects and it provided us satisfactory results as intraoral wound dressing material.

The dynamics of the excited states of 1-aminofluoren-9-one (1AF) and 1-(N,N-dimethylamino)-fluoren-9-one (1DMAF) are investigated by using steady-state absorption and fluorescence as well as subpicosecond time-resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen-bonded form in aprotic solvents, the excited-state intramolecular proton-transfer reaction is the only relaxation process observed in the excited singlet (S(1)) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen-bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S(1)(LE), or S(1)(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge-transfer, S(1)(TICT), state. A crossing between the excited-state and ground-state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S(1)(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen-bond-donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen-bonded complex formed between the S(1)(TICT) state and the solvent is possibly avoided and the hydrogen-bonded complex is weakly emissive.

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