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Spectroscopic and Photophysical Characterization of Acetylenic Fluorophores: The Role of the Proximity Effect on Increasing Internal Conversion
Author(s) -
Flamini Rebecca,
Marrocchi Assunta,
Spalletti Anna
Publication year - 2015
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201402448
Subject(s) - solvatochromism , photochemistry , polarity (international relations) , chemistry , polar , internal conversion , solvent , solvent polarity , fluorescence , dipole , solvent effects , singlet state , aryl , derivative (finance) , chemical physics , excited state , organic chemistry , atomic physics , spectral line , economics , cell , biochemistry , physics , alkyl , quantum mechanics , astronomy , financial economics
The spectroscopic and photophysical behavior of a series of six extended arylacetylenes and one 1,3‐diyne derivative was studied in solvents of different polarity to gain insight into the relationships between molecular architecture and optical/photophysical properties. The radiative decay channel was revealed to be the most important one for all the compounds, particularly in nonpolar solvents. A notable fluoro‐solvatochromism was observed for the 1,3‐diyne derivative in line with the large increase of its dipole moment under excitation. A peculiar behavior was observed for nitro‐substituted aryl acetylenes on increasing solvent polarity, which was explained by the presence of an upper forbidden singlet state (S 2 ) that is more polar than the allowed S 1 state; this was confirmed by quantum mechanical calculations. The large decrease of the S 2 –S 1 energy gap in a moderately polar solvent causes a strong increase of S 1 –S 0 internal conversion to the detriment of fluorescence, which is in agreement with Lim’s proximity effect model.