Photoinduced Intramolecular Charge Transfer and Hyperpolarizability Coefficient in Push‐Pull Pyridinium Salts with Increasing Strength of the Acceptor Group

Abstract

The synthesis of three push‐pull cationic dyes is reported here together with a photophysical study carried out by stationary and ultrafast spectroscopies. The hyperpolarizability (β) values of the three molecules have been estimated through a simple solvatochromic method based on conventional, low‐cost equipment, which had been tested previously with success in our laboratory. The investigated pyridinium salts showing strong negative solvatochromism bear the same piperidine ring as a strong electron‐donor group and the same thiophenes as electron‐rich π‐linkers, but differ in terms of the N‐substituent on the electron‐acceptor pyridinium unit, namely N‐methyl in compound A, N‐pyrimidin‐2yl in B and N‐2,4‐dinitrophenyl in C. The derived β values were found to increase (in the order A<B<C) along with the increasing electron‐acceptor strength of the pyridinium substituent, with the highest polarizability being estimated for the derivative bearing the strongest electron‐withdrawing substituent dinitrobenzene. State‐of‐the‐art femtosecond transient absorption measurements evidenced fast kinetics and dynamics in the singlet excited state in agreement with charge transfer (CT) processes promoted by excitation, with a proper ICT state observed in the case of C. This finding confirms the efficiency of photoinduced intramolecular CT as a significant factor that affects the NLO response.

New Di(heteroaryl)ethenes as Apoptotic Anti‐proliferative Agents Towards Breast Cancer: Design, One‐Pot Synthesis and In Vitro Evaluation

“… Synthesis of the designed compounds.N‐(2‐pirimidyl)‐4‐picolinium and N‐(2,4‐dinitrophenyl)‐4‐picolinium ions were synthesized as stable PF 6 − salts following literature procedure, while N‐methyl‐4‐picolinium iodide was converted to the PF 6 − salt by precipitation from water/aqueous NH 4 PF 6 …”

“… take advantage of the 5‐substituted furan moiety, as this pentatomic ring is present in some of the most active compound of the previous in vitro tests; understand the biological activity of different N‐substituent on the pyridinium unit linked in 4 position, as these substitution pattern accounts for interesting optical properties but has never been evaluated for the design of anti‐proliferative agents. …”

Synthesis, optical and electrochemical properties of a series of push-pull dyes based on the 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile (TCF) acceptor

“…In recent decades, push-pull dyes have attracted a lot of attention due to their numerous applications ranging from non-linear optics (NLO) [1][2] to organic photovoltaics (OPV), [3][4] organic field effect transistors (OFET), [5] organic light emitting diodes (OLED) [6] and polymerization photoinitiators. [7][8][9][10][11][12] Typically, push-pull dyes are molecules comprising an electron donor and an electron acceptor connected by mean of a π -conjugated and planar system.…”

New push-pull dyes based on 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile: An amine-directed synthesis

“…During the past decades, a great deal of efforts has been devoted to design push-pull chromophores as these structures can find applications in numerous research fields ranging from Non-Linear Applications (NLO) [1][2][3][4][5][6] to Organic Photovoltaics (OPVs) [7][8][9][10][11][12], Organic Fields Effects Transistors (OFETs) [13], Organic Light-Emitting Diodes (OLEDs) [14] and photoinitiators of polymerization [15][16][17][18][19]. Typically, a push-pull compound is composed of an electron donor connected to an electron acceptor by mean of a conjugated or a non-conjugated spacer but dyes comprising a conjugated spacer are the most popular ones.…”