Ribbon ToggleButton
The RadRibbonToggleButton represents an extension of the RadToggleButton. It provides an easier interaction with the RadRibbonView control. What is special about the RadRibbonToggleButton is that it has two states - checked and unchecked. To switch between these states just click on it.
To learn more about the RadToggleButtonButton control read its documentation. RadRibbonToggleButton
<telerik:RadRibbonToggleButton CollapseToMedium="Never"
CollapseToSmall="WhenGroupIsMedium"
IsAutoSize="True"
LargeImage="Icons/32/Equation.png"
Size="Large"
SmallImage="Icons/16/Equation.png"
Text="Symbol" />

Handling Changes in the the Button's Checked State
Besides the Click event, the RadRibbonToggleButton control exposes two additional events - Checked and Unchecked. They are meant to notify for changes in the checked state of the toggle button.
<telerik:RadRibbonToggleButton Checked="RadRibbonToggleButton_Checked"
CollapseToMedium="Never"
CollapseToSmall="WhenGroupIsMedium"
IsAutoSize="True"
LargeImage="Icons/32/Equation.png"
Size="Large"
SmallImage="Icons/16/Equation.png"
Text="Symbol"
Unchecked="RadRibbonToggleButton_Unchecked" />
private void RadRibbonToggleButton_Checked(object sender, RoutedEventArgs e)
{
}
private void RadRibbonToggleButton_Unchecked(object sender, RoutedEventArgs e)
{
}
Private Sub RadRibbonToggleButton_Checked(sender As Object, e As RoutedEventArgs)
End Sub
Private Sub RadRibbonToggleButton_Unchecked(sender As Object, e As RoutedEventArgs)
End Sub