How to save picture to desktop by naming "now" statement!

[HerryMarkowitz]

Greetings,
I want to export chart to the desktop as picture.
Following code is okey. Following code exports chart to the desktop as picture named Example.

If Len(Dir(Environ("USERPROFILE") & "\Desktop\Excel Charts\", vbDirectory)) = 0 Then MkDir Environ("USERPROFILE") & "\Desktop\Excel Charts\"
ActiveChart.Export Filename:=Environ("USERPROFILE") & "\Desktop\Excel Charts\" & "Example.png", FilterName:="png", Interactive:=False

I want to export chart to the desktop as picture named current date and time. So,I am using "now" statement.
Following code is not okey.
Red line need to be corrected.

If Len(Dir(Environ("USERPROFILE") & "\Desktop\Excel Charts\", vbDirectory)) = 0 Then MkDir Environ("USERPROFILE") & "\Desktop\Excel Charts\"
ActiveChart.Export Filename:=Environ("USERPROFILE") & "\Desktop\Excel Charts\" & Now & ".png", FilterName:="png", Interactive:=False

As a result picture name must be "2015.06.17.01.20"

Thanks in advance.