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The Role of Hydrogen‐Bonding Interactions in the Ultrafast Relaxation Dynamics of the Excited States of 3‐ and 4‐Aminofluoren‐9‐ones
Author(s) -
Mondal Jahur A.,
Samant Vaishali,
Varne Mahendra,
Singh Ajay K.,
Ghanty Tapan K.,
Ghosh Hirendra N.,
Palit Dipak K.
Publication year - 2009
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200900325
Subject(s) - solvation , chemistry , excited state , hydrogen bond , intermolecular force , intramolecular force , relaxation (psychology) , photochemistry , solvent effects , protic solvent , solvent , singlet state , chemical physics , ground state , computational chemistry , molecule , atomic physics , organic chemistry , psychology , social psychology , physics
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 ( τ 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.